Entire Report - May 2012


National Overview

NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.

Maps and Graphics

Temperature and Precipitation Ranks
U.S. Percentage Areas
More Information

National Overview:



May Extreme Weather/Climate Events

Supplemental May and January-May Information



Alaska Temperature and Precipitation:

  • Alaska had its 22nd coolest May since records began in 1918, with a temperature 2.2°F (1.2°C) below the 1971–2000 average.
  • Alaska had its 23rd coolest March-May since records began in 1918, with a temperature 2.7 °F (1.5°C) below the 1971–2000 average.
  • Alaska had its 15th coolest January-May since records began in 1918, with a temperature 3.2°F (1.8°C) below the 1971–2000 average.
  • Alaska had its 19th wettest May since records began in 1918, with an anomaly that was 19.8 percent above the 1971–2000 average.
  • Alaska had its 38th wettest March-May since records began in 1918, with an anomaly that was 10.5 percent above the 1971–2000 average.
  • Alaska had its 32nd wettest January-May since records began in 1918, with an anomaly that was 13.1 percent above the 1971–2000 average.

For additional details about recent temperatures and precipitation across the U.S., see the Regional Highlights section below and visit the Climate Summary page". For information on local temperature and precipitation records during the month, please visit NCDC's Records page. For details and graphics on weather events across the U.S. and the globe please visit NCDC's Global Hazards page.


Regional Highlights:

These regional summaries were provided by the six Regional Climate Centers and reflect conditions in their respective regions. These six regions differ spatially from the nine climatic regions of the National Climatic Data Center.

  • Northeast Region: (Information provided by the Northeast Regional Climate Center)
  • May 2012 was the 14th consecutive warmer-than-normal month in the Northeast. The region’s average temperature of 61.1 degrees F (16.2 degrees C) was 4.8 degrees F (2.6 degrees C) above normal and 2.3 degrees F (1.3 degrees C) warmer than May 2011. It was the warmest May since 1991 and the 5th warmest since 1895. Each of the states in the Northeast averaged on the warm side of normal, with departures that ranged from +2.1 degrees F (1.2 degrees C) in Rhode Island to +6.1 degrees F (3.4 degrees C) in Pennsylvania. The monthly average at eleven of the Northeast states ranked between the third and ninth warmest since 1895; Maine’s average placed that state at 17th warmest in 118 years. Temperature averages for the spring (May-June) of 2012 were also above normal. The Northeast’s average was 50.8 degrees F (10.4 degrees C), which was 5.1 degrees F (2.8 degrees C) above normal. It was the warmest spring since 1895 in the Northeast and in ten of the states. Rhode Island saw its 2nd warmest spring in 118 years and Maine, its third warmest. The year-to-date temperatures were also the warmest since 1895 in the Northeast and in ten states. Maine and Pennsylvania missed the number one spot, but were close each ranked 2nd warmest for this time period.
  • After three months of below normal precipitation totals, the Northeast averaged 118 percent of normal in May. Precipitation was not evenly distributed New Hampshire’s total was 157 percent of normal, while Delaware’s was only 49 percent of May’s normal monthly total. For the 118 years of record, New Hampshire ranked 7th wettest, Vermont 9th, and Pennsylvania, 22nd, while Delaware ranked 24th driest. Spring 2012 precipitation totals averaged below normal in the Northeast (91 percent) and in nine of the twelve states in the region. The wetter-than-normal states were Maine, Vermont, and West Virginia, with totals that were 105, 104, and 105 percent of normal, respectively. March through May departures among the drier-than-normal states ranged from 56 percent in Delaware to 98 percent in New Hampshire. State and regional precipitation totals for the January through May time period were all below normal. The Northeast average was 87 percent of normal and state departures ranged from 97 percent in West Virginia to 49 percent in Delaware. It was the driest January through May since 1895 in Delaware, the 3rd driest in Connecticut, the 6th driest in Maryland, and the 10th driest in New Jersey.
  • Rainfall during the month resulted in fewer areas of abnormally dry (D0), moderate drought (D1) and severe drought (D2) in the region. The May 27, 2012 U.S. Drought Monitor still had moderate (D1) and severe (D2) drought in Delaware, with pockets of D1 drought in Connecticut, Maryland and Massachusetts. New Jersey, most of New Hampshire and southeastern Maine improved from D1 drought to D0 at month’s end.
  • Fruit growers in New York were starting to assess the damage caused by abnormally warm temperatures in March followed by freeze conditions in April. Estimates from Cornell’s Lake Erie Regional Research Laboratory put crop losses for grapes at 40-50%, cherries at 100%, peaches at 90%, and apples at 50%. New York is the second largest apple producer in the country with an economic impact of over $200 million. The actual loss to fruit growers won’t be available until the crop is harvested.
  • For more information, please go to the Northeast Regional Climate Center Home Page.
  • Midwest Region: (Information provided by the Midwest Regional Climate Center)
  • May temperatures were above normal across the Midwest. Temperatures ranged from 1 degree F (1 C) above normal in northwest Minnesota to 7 degrees F (4 C) above normal in eastern Ohio. Preliminary numbers ranked Ohio, Kentucky, Indiana, Michigan, Illinois, Wisconsin, and Missouri among the ten warmest Mays dating back to 1895. Spring temperatures ranked as the warmest on record for all nine Midwest states. Temperatures departures for the March to May season ranged from 4 to 9 degrees F (2 to 5 C) above normal. All nine Midwest states have recorded above normal temperatures for the last seven months or more.
  • May precipitation varied with much of the northern third of the Midwest recording above normal precipitation including a large swath of Minnesota that received two to three time normal. The southeast parts of the Midwest were close to normal while much of Missouri, Illinois, Indiana, southern Michigan, and southeast Iowa received only 25 to 75 percent of normal. Spring precipitation was also heaviest across Minnesota with totals ranging from 150 to 200 percent of normal. The driest areas for spring extended from northwest Ohio into Illinois.
  • Severe weather reports were down from earlier in the spring, and compared to average for May, but still were widespread. In May, 22 of 31 days had reports of severe weather in the Midwest with no reports on the 8th through the 14th nor on the 16th or 17th. All nine states in the region reported severe weather in both the first and last week of May. All but one of the Midwest tornadoes came in the first six days of the month.
  • Drought in Minnesota and northwest Iowa eased with May rains running two to three times normal. Other Midwest locations saw drought worsen as lack of rain, combined with enhanced evapotranspiration, dried out the upper soil layers. Drought conditions worsened in northwest Minnesota and for most of the southern two-thirds of the Midwest. Severe Drought was limited to western Kentucky, extreme southern Illinois, and the boot heel of Missouri but many areas saw drying of the topsoil, stressed plants, and dry lawns as concerns increased about the potential for drought to rapidly worsen.
  • The many days of dry conditions in the Midwest allowed farmers to spend more time in the fields, thus corn and soybean planting was running ahead of normal. With much of the crop in the ground by the end of the month, farmers were hoping for adequate rains to replenish soil moisture and supply needed water to stressed plants going into the hot summer months.
  • For details on the weather and climate events of the Midwest, see the weekly summaries in the Midwest Climate Watch page.
  • Southeast Region: (Information provided by the Southeast Regional Climate Center)
  • Mean temperatures in May were generally above average across the Southeast region. The greatest departures were found across parts of Virginia and North Carolina, where monthly temperatures were 4 to 5 degrees F (2.2 to 2.8 degrees C) above average. Temperatures across much of South Carolina, Georgia, Alabama, and northern Florida were 2 to 3 degrees F (1.1 to 1.6 degrees C) above average, while temperatures across south Florida, Puerto Rico, and the U.S. Virgin Islands were near average (i.e. within 1 degree F or 0.5 degrees C) for the month. Several locations recorded one of their warmest May's on record, including Cape Hatteras, NC (2nd warmest), Fort Myers, FL (3rd warmest), Washington D.C. (4th warmest), and Tampa, FL (5th warmest). As in April, the month of May began with record-breaking temperatures across a large part of the region. Over 150 daily maximum and 200 daily high minimum temperature records were tied or broken from the 1st to the 7th of the month. More record-breaking warmth was observed at the end of the month, as temperatures reached 100 degrees F (37.8 degrees C) for the first time this year across southern portions of Alabama and Georgia, as well as across central and northern portions of Florida. Over 200 daily maximum and 250 daily high minimum temperature records were tied or broken from the 25th to the 31st of the month. More than 20 locations recorded their warmest meteorological spring (March-May) on record, including Birmingham, AL, Washington D.C., Tampa, FL, Tallahassee, FL, Atlanta, GA, Columbia, SC, Charleston, SC, Charlotte, NC, Asheville, NC, Raleigh-Durham, NC, Richmond, VA, and Roanoke, VA.
  • Monthly precipitation totals were variable across the Southeast region in May. Much of this variability was due to the passage of Tropical Storm Beryl, which dropped between 2 and 7 inches (50.8 and 177.8 mm) of rain across large parts of northeast Florida and eastern sections of Georgia, the Carolinas, and extreme southeastern Virginia, and as much as 10 inches (254 mm) of rain across central portions of the Florida Panhandle, from the 28th to the 31st of the month. This contributed to monthly precipitation totals that ranged between 150 and 300 percent of normal. In addition, several locations across central North Carolina and Virginia, southern Alabama, and south Florida also exhibited above normal precipitation for the month. A disturbance ahead of Beryl dropped nearly 10 inches (254 mm) of rain in Miami, FL on the 22nd of the month, making it one of the wettest 24-hour periods in a record extending back to 1898. Remarkably, the rain gauge at the Miami International Airport recorded 4.4 inches (111.76 mm) in just one hour during the event. This capped off the wettest meteorological spring on record in Miami, FL with 27.49 inches (698.25 mm). Conversely, much of the interior of the Southeast remained dry in May, with monthly precipitation generally less than 50 percent of normal. Monthly precipitation was near normal across most of Puerto Rico and the U.S. Virgin Islands.
  • There were 509 reports of severe weather across the Southeast in May, including nine confirmed tornadoes. Four of these occurred in association with Tropical Storm Beryl. In Florida, two homes suffered roof damage from an EF-0 tornado in St. Lucie County, while damage to trees and mangroves was reported when a waterspout moved onshore in Levy County, also resulting in an EF-0 rating. In Orangeburg County, SC, an EF-1 tornado uprooted several trees and destroyed a corn field near the town of Holly Hill. Another EF-1 tornado was confirmed in Carteret County, NC, where at least 60 homes were damaged and three homes were destroyed in the town of Peletier. Four of the remaining five tornadoes in May were rated EF-0, including two waterspouts that moved onshore in Pinellas and Escambia Counties in Florida, while an EF-1 tornado on the 14th of the month blew the roofs off of several homes in the town of Rockingham in Richmond County, NC.
  • The Southeast was impacted by two tropical storms in May, marking just the third time since 1851 that two tropical cyclones formed prior to the official start of the Atlantic hurricane season. On the 19th of the month, Tropical Storm Alberto formed off of the Southeast coast, with peak winds of 60 mph (26.8 m/s). The storm produced 3 to 5 foot (0.9 to 1.5 m) waves as well as dangerous rip currents along the North and South Carolina coasts that resulted in several ocean rescues. A little more than a week later, Tropical Storm Beryl made landfall near Jacksonville Beach, FL with peak winds of 70 mph (31.3 m/s), making it the strongest tropical cyclone observed along the Atlantic coast in May in over 100 years. Several thousand customers lost power across northern Florida. In addition to heavy rain and high wind, Beryl contributed to strong rip currents and storm surge flooding along much of the Atlantic coast, which resulted in the death of a teenage boy in Daytona Beach, FL. One other death was confirmed from Beryl when a tree fell on a car along a rural highway in Orangeburg County, SC, killing the driver.
  • The rainfall from Tropical Storm Beryl helped alleviate drought conditions across eastern sections of the Southeast. Improvements of one to two drought categories in the U.S. Drought Monitor were noted across parts of the Florida Panhandle, southeastern Georgia, and the coastal plain of the Carolinas. Although the rainfall from Beryl helped extinguish several fires across northern Florida, an estimated 60 fires were still active across 10,000 acres (40.5 sq km) of the state at the end of the month. Crop damage due to hail was reported across several counties in Georgia, including several hundreds of acres of watermelon and other crops that were approaching harvest. The warm, dry weather that persisted across much of the Southeast this spring resulted in reduced wheat yields across Florida, while peach volumes were down between 25 and 35 percent across Georgia due to a lack of accumulated chill hours. On the other hand, several vegetable and commodity crops were able to ship early due to favorable weather conditions.
  • For more information, please go to the Southeast Regional Climate Center Home Page.
  • High Plains Region: (Information provided by the High Plains Regional Climate Center)
  • May 2012 was largely warm and dry across the High Plains Region. The largest temperature departures occurred in southern portions of the Region, where the departures from normal temperature ranged from 4.0-8.0 degrees F (2.2-4.4 degrees C) above normal. The only areas in the Region to have lower than normal temperatures were central and western North Dakota and pockets of Wyoming and South Dakota. Many locations across the Region were ranked in the top 10 warmest Mays on record. For instance, Topeka, Kansas had its 2nd warmest May on record with an average temperature of 71.4 degrees F (21.9 degrees C). The record of 72.7 degrees F (22.6 degrees C) was set back in 1962 (period of record 1887-2012). Many locations set daily records as temperatures soared near the end of the month. Some locations even had their earliest 100 degrees F (37.8 degrees C) day on record. Scottsbluff, Nebraska set a daily record of 100 degrees F (37.8 degrees C) on May 22nd, absolutely crushing the old record of 91 degrees F (32.8 degrees C) set back in 1939 (period of record 1893-2012). Not only was this a new daily record, this was also the earliest 100 degrees F (37.8 degrees C) day on record in Scottsbluff. On average, temperatures there do not reach 100 degrees F (37.8 degrees C) until July 3rd. Prior to this new record, the earliest 100 degrees F (37.8 degrees C) day was May 28th (1934). According to the National Agricultural Statistics Service, the earliest start to the wheat harvest in Kansas since records began in 1952 has occurred this year. By the end of the month, at least 4 percent of the wheat harvest was complete. The earliest harvest prior to this year occurred in 1962 when 1 percent of the crop had been harvested by June 2nd. The dry, hot, and windy weather in Nebraska led to low soil moisture which caused producers to turn on pivots to aid in crop germination. Although rain was a welcome sight to some, the tornadoes and hail that accompanied the storms led to crop damage which will require producers to replant in some areas of Nebraska. This spring (March, April, and May) was a record breaker across the entire High Plains Region. Average temperatures were above normal at all locations in the Region and the largest temperature departures occurred in the east as areas of South Dakota, Nebraska, and Kansas had average temperatures which were over 8.0 degrees F (4.4 degrees C) above normal. Most locations set new records or were at least ranked in the top 5 warmest springs on record. Some of the impressive records include those set in Lincoln, Nebraska and Wichita, Kansas. Lincoln had an average temperature of 59.3 degrees F (15.2 degrees C) which was 8.5 degrees F (4.7 degrees C) above normal and beat its old record of 56.1 degrees F (13.4 degrees C), set in 1977, by 3.2 degrees F (1.8 degrees C) (period of record 1887-2012). Wichita had an average temperature of 64.4 degrees F (18.0 degrees C), which was 9.0 degrees F (5.0 degrees C) above normal and beat its old record of 59.9 degrees F (15.5 degrees C) by a whopping 4.5 degrees F (2.5 degrees C) (period of record 1888-2012).
  • May 2012 was dry for much of the High Plains Region. A large area encompassing southern Wyoming, western and southern Nebraska, northern and western Kansas, and the east and west sides of Colorado had precipitation totals which were less than 50 percent of normal. In addition, many locations within that area received only 25 percent or less of normal precipitation and ranked in the top 10 driest Mays on record. Goodland, Kansas had its 2nd driest May on record with only 0.45 inches (11 mm) of precipitation, which was 13 percent of normal precipitation (period of record 1895-2012). The 1927 record held at 0.31 inches (8 mm). Snowpack in Colorado and Wyoming continued to decline. According to the Natural Resources Conservation Service, by the end of the month, the statewide snowpack was just 5 percent of average in Colorado and 22 percent of average in Wyoming. According to the Denver Post, the low snowpack has raised concerns about potential impacts on river recreation in Colorado. Although the majority of the Region was drier than normal, a few areas had above normal precipitation totals including eastern South Dakota, northeastern Nebraska, south-central Colorado, and a few pockets of North Dakota and Wyoming. The highest precipitation amounts were located in eastern South Dakota where totals exceeded 200 percent of normal. Extremely heavy rain fell in eastern South Dakota during the May 5-6 timeframe. The 24-hour precipitation total, ending May 6th, for Madison 2 SE, South Dakota was 4.81 inches (122 mm)! This crushed the old daily record of 3.44 inches (87 mm) set back in 2007 and also set a new 1-day May precipitation record (period of record 1961-2012). The old 1-day precipitation total was 3.79 inches (96 mm), set on May 1, 1972. By the end of the month, this had become the wettest May on record for Madison 2 SE with a total of 9.97 inches (253 mm). The old record of 8.53 inches (217 mm) occurred in 1972. In addition, this also became the wettest month on record for Madison 2 SE, beating out the old record of 9.57 inches (243 mm) which occurred in June 1984. Spring (March, April, and May) precipitation and snowfall totals were some of the lowest on record in the western part of the High Plains Region. A large area of the Region had precipitation totals which were 25-50 percent of normal including southern Wyoming, the panhandle of Nebraska, and western and northern Colorado. Some examples of the dryness include Cheyenne, Wyoming and Boulder, Colorado. Cheyenne had its 2nd driest spring on record with only 0.69 inches (18 mm) of liquid equivalent precipitation. This was not far off from the record 0.67 inches (17 mm) which was set in the spring of 1880 (period of record 1871-2012). In addition, Cheyenne had its least snowy spring on record with only 0.6 inches (2 cm) of snowfall. This beat the old record of 3.5 inches (9 cm) which occurred in 2007 (snowfall period of record 1883-2012). Similarly, Boulder, Colorado had its 3rd driest spring with 3.10 inches (79 mm) of precipitation. The record 2.21 inches (56 mm) which fell in 1925 was able to hold on (period of record 1893-2012). Boulder also had its least snowy spring on record with a mere 1.6 inches (4 cm) of snowfall. This easily beat the old record of 3.5 inches (9 cm) which fell in 1982 and was incredibly lower than the average spring snowfall, which in Boulder is 29.5 inches (75 cm).
  • There were many changes again to the U.S. Drought Monitor this month. Improvements were made in eastern South Dakota and Nebraska as drought conditions were eliminated due to ample precipitation. Only small areas of abnormally dry conditions (D0) remained there. Moderate drought conditions (D1) were erased from western South Dakota and the majority of western North Dakota as well. Unfortunately, drought conditions elsewhere either emerged or worsened over the course of the month. D1 conditions in eastern North Dakota expanded towards the south. New D0 and patches of D1 have emerged across Kansas. D1 conditions also expanded further across southern Colorado and also across the panhandle of Nebraska and into southern Wyoming and northwestern Colorado. The big story this month was the development of extreme drought conditions (D3) in northwestern Colorado due to extremely low precipitation. According to the U.S. Seasonal Drought outlook released on May 17th, drought conditions were expected to improve in areas of North Dakota and the panhandle of Nebraska. Drought conditions in Colorado, southern Wyoming, and southwestern Kansas were expected to persist.
  • For more information, please go to the High Plains Regional Climate Center Home Page.
  • Southern Region: (Information provided by the Southern Regional Climate Center)
  • As was the case in the past few months, the Southern Region experienced yet another warmer than normal month in May. Temperature values were slightly higher in the northern half of the region, ranging from 4 to 8 degrees F (2.22 to 4.44 degrees C) above normal, while in the southern half of the region, values ranged from approximately 2 to 4 degrees F (1.11 to 2.22 degrees C) above normal. Arkansas, Oklahoma and Tennessee had the highest state temperature rankings in the region. Arkansas experienced its fourth warmest May on record, with a state average temperature of 73.10 degrees F (22.83 degrees C). For Oklahoma, it was the fifth warmest May on record (1895-2012), while for Tennessee, it was their sixth warmest May on record (1985-2012). Oklahoma had a state wide temperature average of 72.20 degrees F (22.30 degrees C), while Tennessee had a state wide temperature average of 70.40 degrees F (21.33 degrees C). Temperature rankings were also high in the three remaining states. Texas experienced its eleventh warmest May on record (1895-2012) with a state average temperature of 75.40 degrees F (24.11 degrees C). In Louisiana, the state average temperature was 76.00 degrees F (24.44 degrees C) or the twelfth warmest May on record (1895-2012). Mississippi had its fourteenth warmest May on record (1895-2012) with a state average temperature o f 74.00 degrees F (23.33 degrees C).
  • With the exception of southwestern Texas, May was a rather dry month for the bulk of the Southern Region. Precipitation was scarce in the central portions of the region where most stations recorded less than one fourth of the normal monthly totals. This was also the case for most of the Texas and Oklahoma panhandle region. Elsewhere, values ranged mostly between twenty-five and fifty percent of normal. Southwestern Texas was the only portion of the region that observed above normal rainfall, with precipitation totals ranging from one and one half to four times of normal. Despite that, Texas' state wide precipitation average was slightly on the dry side with a total of 2.81 inches (71.37 mm). Arkansas, Oklahoma and Louisiana had the highest state-wide precipitation rankings. For Oklahoma, which received a total of 2.33 inches (59.18 mm), it was the eleventh driest May on record (1895-2011). It was the second driest May on record in Arkansas, which saw only 1.63 inches (41.40 mm) of precipitation. Louisiana averaged 2.26 inches (57.40 mm) of precipitation, which makes it their fifteenth driest May on record (1895-2012). For Mississippi, it was the thirty-third driest May on record, which is based on a state-wide precipitation total of 3.05 inches (77.47 mm). Lastly, Tennessee experienced its twenty-eighth driest May on record, with a state wide precipitation total of 3.26 inches (82.80 mm).
  • Consistent dryness over much of the Southern Region has led to an expansion of drought in some areas, while above average precipitation has led to improvements in other areas. In the case of the latter, high precipitation in southwestern Texas, has led to the removal of all exception drought in that portion of the state. Though moderate drought remains, this is a significant improvement over last month, where most of the area was riddled with severe to extreme drought. In northern Arkansas, where precipitation was below normal for much of the month, there has been an introduction of moderate drought. This also includes portions of northeastern Mississippi and western Tennessee, where conditions were also drier than normal over the past several weeks.
  • On May 10, 2012, over a dozen tornadoes touched down in southern Texas. In La Salle County, two people were reported injured.
  • For more information, please go to the Southern Regional Climate Center Home Page.
  • Western Region: (Information provided by the Western Regional Climate Center)
  • May is typically a month in which temperatures increase and precipitation totals have begun to wane in the coastal and southern West as the Pacific storm track edges northward and the Southwest Monsoon system has yet to develop. May 2012 showed few exceptions to this trend. Many Southwest locations received no precipitation at all, and only a smattering of stations in the Northwest and along the Mexico border recorded average to above-average precipitation. The northern tier of the region experienced cooler than normal average temperatures this month, while in the Southwest, average temperatures were generally above the May mean. Severe fire weather dominated the Southwest, leading to the rapid development of several large wild land fires and New Mexico experiencing its largest fire on record.
  • Many locations the Southwest were dry this month, not uncommon in Mays past. For the 31st time in the last 75 years, Las Vegas, Nevada received no measureable precipitation (less than 0.01 in / 0.25 mm) in May. Further west, Santa Barbara, California has 25 years in its 71-year record with no measurable May precipitation. Other zero-precipitation locations this month include Yuma and Flagstaff, Arizona and Palm Springs, California. To the north, central Washington and Oregon have seen drought development over the last few months. This month, Spokane, Washington received only 0.69 in (17.5 mm) rainfall, the 28th driest May in the station’s 112-year record. Western Washington and Oregon fared better, with Seattle, Washington and Portland, Oregon notching several daily precipitation records toward month’s end. Rainfall at Portland totaled 3.37 in (85.6 mm), tied for 14th wettest May since records began in 1938. Glasgow, Montana also saw above average precipitation, receiving 3.06 in (77.7 mm) and 11th wettest May in a 57-year record. Mid-month thunderstorm activity along the US-Mexico border helped to alleviate exceptional drought conditions in some specific locations. Las Cruces, New Mexico received 0.58 in (14.7 mm) of rain, tying for the 22nd wettest May in the past 120 years at that location.
  • Temperatures in the Northwest and along the coast this month were 2-4 F (1-2 C) below normal, similar to but less cool than May 2010 and 2011. Average May temperatures do not show recent warming or cooling in the Northwest, though the past two years were anomalously cool. The Southwest saw temperatures 2-6 F (1-3 C) above normal, breaking the cool May pattern of 2010 and 2011, and back to the general trend of increasing May temperatures in the Southwest over the past 30 years.
  • A significant consequence of the continued warm and dry March, April, and May has been a drastic lowering of the expected summer snowmelt in the Intermountain West. Forecasts of Colorado River inflow to Lake Powell have dropped very far, and now rank among the 3rd or 4th lowest in the past century.
  • May (all month): Fires throughout Southwest: Critical fire conditions (low relative humidity, high wind, drought conditions) were in place for most of May in the southwest, allowing wildfires to develop and spread rapidly.
  • New Mexico: The Whitewater-Baldy Complex Fire, ignited by lightning on May 16, has become New Mexico’s largest fire on record. As of June 1, 216,650 acres (87,865 hectares) had burned and the fire was only 10% contained.
  • Arizona: The Gladiator Fire, approximately 20 mi (32 km) north of Phoenix, Arizona began May 16 and had burned 16,240 acres (6,572 hectares) and was 45% contained as of June 1. The fire was a human-caused structure fire and forced mandatory evacuation of the town of Crown King, Arizona. The Sunflower Fire, 30 mi (48 km) north of Mesa, Arizona began May 12 and had consumed 17,618 acres (7,129 hectares) and stood at 80% contained on June 1.
  • Nevada: The Topaz Ranch Estates Fire, 60 mi (97 km) south of Reno, Nevada, began May 22 and burned 7,152 acres (2,894 hectares). The human-caused fire destroyed two residences and 17 structures.
  • Colorado: The Hewlett Fire in the Roosevelt National Forest began May 14 and burned 7685 acres (3,110 hectares) before containment. The Sunrise Mine Fire began May 25 4 mi (6 km) north of Paradox, Colorado. By June 1 it had consumed 6,192 acres (2,505 hectares) and was 85% contained. Both fires were human-caused.
  • May 26: Four Corners Dust Storm: Southwest winds in excess of 50 mph (80 kph) associated with a deep trough drove a dust storm into the Four Corners region. The dust, combined with smoke from fires in New Mexico, reduced visibility to less than a mile (1.6 km).
  • For more information, please go to the Western Regional Climate Center Home Page.

See NCDC's Monthly Records web-page for weather and climate records for the most recent month. For additional national, regional, and statewide data and graphics from 1895-present, for any period, please visit the Climate at a Glance page.


PLEASE NOTE: All of the temperature and precipitation ranks and values are based on preliminary data. The ranks will change when the final data are processed, but will not be replaced on these pages. Graphics based on final data are provided on the Temperature and Precipitation Maps page and the Climate at a Glance page as they become available.

Global Analysis

Contents of this Section:


May 2012 Selected Climate Anomalies and Events MapMay 2012 Selected Climate
Anomalies and Events Map

Global Highlights

  • The combined global land and ocean average surface temperature for May 2012 was 0.66°C (1.19°F) above the 20th century average of 14.8°C (58.6°F). This is the second warmest May since records began in 1880, behind only 2010.

  • The Northern Hemisphere land and ocean average surface temperature for May 2012 was the all-time warmest May on record, at 0.85°C (1.53°F) above average.

  • The globally-averaged land surface temperature for May 2012 was the all-time warmest May on record, at 1.21°C (2.18°F) above average.

  • ENSO-neutral conditions continued during May 2012 and sea surface temperature anomalies in the eastern equatorial Pacific Ocean continued to warm. The May worldwide ocean surface temperatures ranked as the 10th warmest May on record.

  • For March–May (boreal spring) 2012, the combined global land and ocean surface temperature was 0.59°C (1.06°F) above average—the seventh warmest such period on record.

  • The combined global land and ocean average surface temperature for January–May 2012 was the 11th warmest on record, at 0.50°C (0.90°F) above the 20th century average.


==global-temps-errata==

Please Note: The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed. Effective with the July 2010 State of the Climate Report, NCDC transitioned to the new version (version 3b) of the extended reconstructed sea surface temperature (ERSST) dataset. ERSST.v3b is an improved extended SST reconstruction over version 2. For more information about the differences between ERSST.v3b and ERSST.v2 and to access the most current data, please visit NCDC's Global Surface Temperature Anomalies page.


Introduction

Temperature anomalies for May 2012 and March – May 2012 are shown on the dot maps below. The dot maps on the left provide a spatial representation of anomalies calculated from the Global Historical Climatology Network (GHCN) dataset of land surface stations using a 1961–1990 base period. The dot maps on the right are a product of a merged land surface and sea surface temperature (SST) anomaly analysis developed by Smith et al. (2008). For the merged land surface and SST analysis, temperature anomalies with respect to the 1971–2000 average for land and ocean are analyzed separately and then merged to form the global analysis. For more information, please visit NCDC's Global Surface Temperature Anomalies page.

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Temperatures

In the atmosphere, 500-millibar height pressure anomalies correlate well with temperatures at the Earth's surface. The average position of the upper-level ridges of high pressure and troughs of low pressure—depicted by positive and negative 500-millibar height anomalies on the May 2012 height and anomaly mapMay 2012 map—is generally reflected by areas of positive and negative temperature anomalies at the surface, respectively.

May

With the dissipation of La Niña during boreal spring, the May 2012 average temperature across global land and ocean surfaces climbed to 0.66°C (1.19°F) above the 20th century average. This places May 2012 as the second warmest May in the 133-year period of record, falling 0.05°C (0.09°F) short of the record warmth of 2010, a month when a nearly year-long warm phase El Niño had just ended. The Northern Hemisphere experienced its all-time warmest May on record, at 0.85°C (1.53°F) above average, breaking the record previously set in 2010. The Southern Hemisphere temperature anomaly was not quite as dramatic, but still ranked ninth warmest among all Mays on record, at 0.47°C (0.85°F) above average.

Considering land surfaces only, the average global temperature was record warm for May, at 1.21°C (2.18°F) above average, surpassing the previous record warmth set in 2010 by 0.10°C (0.18°F). The Northern Hemisphere was also record warm, at 1.47°C (2.65°F) above average, easily breaking the 2010 record by 0.27°C (0.49°F). The Southern Hemisphere land surface temperature for May was also warmer than average with a positive anomaly of 0.52°C (0.94°F), ranking as the 18th warmest such period on record. Much warmer-than-average monthly temperatures were observed across most of Europe, Asia, northern Africa, most of North America, and southern Greenland. Only Australia, Alaska, and the western U.S. / Canadian border region were notably cooler than average.

  • According to Australia's Bureau of Meteorology, the nationally-averaged maximum (daytime) temperature was near average (+0.3°C / 0.5°F), while the average minimum (nighttime) temperature was well below average (-1.6°C / -2.9°F), ranking as the fifth coolest May nighttime temperature in the country's 63-year period of record. The Murray-Darling Basin and the state of New South Wales each reported their third coolest May nighttime temperatures.

  • Spain experienced its fourth warmest May since national records began in 1960, with a nationally-averaged temperature that was 2.7°C (4.9°F) above average. Eleven stations across different regions of Spain—the Canary Islands, Andalusia, Murcia, Aragon and Catalonia—observed their highest May temperatures on records.

The average global ocean temperature during May was 0.45°C (0.81°F) above the long-term average, ranking as the 10th warmest May on record. This departure marks the highest monthly anomaly since June 2011 and the second warmest since August 2010, a few months after the last El Niño ended in the eastern and central equatorial Pacific Ocean. During May, the northeastern and central Pacific and parts of the Southern Ocean were cooler than average, while the northwestern Atlantic and the north central Pacific had the most extreme warmth. According to the Climate Prediction Center, there is a 50 percent chance that El Niño conditions will emerge during the second half of 2012.

May Anomaly Rank
(out of 133 years)
Records
°C °F Year(s) °C °F
Global
Land +1.21 ± 0.14 +2.18 ± 0.25 Warmest 1st 2012 +1.21 +2.18
Coolest 133rd 1907 -0.94 -1.69
Ocean +0.45 ± 0.04 +0.81 ± 0.07 Warmest 10th 1998 +0.57 +1.03
Coolest 124th 1911 -0.52 -0.94
Land and Ocean +0.66 ± 0.07 +1.19 ± 0.13 Warmest 2nd 2010 +0.71 +1.28
Coolest 132nd 1907 -0.49 -0.88
Northern Hemisphere
Land +1.47 ± 0.15 +2.65 ± 0.27 Warmest 1st 2012 +1.47 +2.65
Coolest 133rd 1907 -1.03 -1.85
Ocean +0.46 ± 0.04 +0.83 ± 0.07 Warmest 6th 2005 +0.58 +1.04
Coolest 128th 1910 -0.55 -0.99
Land and Ocean +0.85 ± 0.08 +1.53 ± 0.14 Warmest 1st 2012 +0.85 +1.53
Coolest 133rd 1907 -0.61 -1.10
Southern Hemisphere
Land +0.52 ± 0.23 +0.94 ± 0.41 Warmest 18th 2002 +1.04 +1.87
Coolest 116th 1917 -1.30 -2.34
Ocean +0.46 ± 0.04 +0.83 ± 0.07 Warmest 10th 1998 +0.62 +1.12
Coolest 124th 1911 -0.52 -0.94
Land and Ocean +0.47 ± 0.06 +0.85 ± 0.11 Warmest 9th 1998 +0.68 +1.22
Coolest 125th 1911 -0.51 -0.92


Season (March–May)

The March–May period ranked as the seventh warmest on record for the seasonally-averaged global land and ocean temperature. The Northern Hemisphere spring ranked as the fourth warmest such period on record, while the Southern Hemisphere autumn was 14th warmest since records began in 1880.

Globally, the average land temperature was the fourth warmest March–May on record, at 1.12°C (2.02°F) above average. Record April and May warmth in the Northern Hemisphere led to record spring warmth over land, with a temperature anomaly of 1.38°C (2.48°F) above the long-term average. That warmth was most pronounced across central Eurasia and most of North America, except the northwest.

  • Austria reported its seventh warmest spring since records began in 1767, according to ZAMG. In the east, the district of Lienz was just 0.2°C (0.4°F) short of the record warmth in May 2007.

  • The United States reported its warmest spring since records began in 1895, with 31 states in the eastern two-thirds of the country observing record warmth. The national temperature was 2.9°C (5.2°F) above its long-term average, surpassing the previous record by 1.1°C (2.0°F). For additional information, please see the U.S. State of the Climate monthly report.

The Southern Hemisphere had an average land temperature that ranked as the 21st warmest March–May on record. The Southern Hemisphere has a much smaller land area than the Northern Hemisphere, thus it has a much lower impact on globally averaged land surface temperatures.

  • Austral autumn was cooler than average across most of Australia, with maximum (daytime) temperatures 0.37°C (0.67°F) below average and minimum (nighttime) temperatures ranking as the fourth lowest on record (-0.93°C / -1.67°F), the lowest since 1994. Autumn nighttime temperatures were the coolest since 1995 in South Australia and coolest since 2000 in Western Australia. La Niña, which tends to have a cooling influence over the country, ended during the season.

As La Niña transitioned to ENSO-neutral conditions during March–May, waters warmed in the eastern and central Pacific Ocean. Overall, the average global ocean temperature for this period was 0.39°C (0.70°F) and ranked as the 11th warmest March–May on record.

March–May Anomaly Rank
(out of 133 years)
Records
°C °F Year(s) °C °F
Global
Land +1.12 ± 0.14 +2.02 ± 0.25 Warmest 4th 2010 +1.26 +2.27
Coolest 130th 1898 -0.81 -1.46
Ocean +0.39 ± 0.04 +0.70 ± 0.07 Warmest 12th 1998, 2010 +0.56 +1.01
Coolest 122nd 1911 -0.53 -0.95
Land and Ocean +0.59 ± 0.08 +1.06 ± 0.14 Warmest 7th 2010 +0.75 +1.35
Coolest 127th 1911 -0.50 -0.90
Northern Hemisphere
Land +1.38 ± 0.17 +2.48 ± 0.31 Warmest 1st 2012 +1.38 +2.48
Coolest 133rd 1898 -0.87 -1.57
Ocean +0.38 ± 0.05 +0.68 ± 0.09 Warmest 8th 2010 +0.56 +1.01
Coolest 126th 1910 -0.51 -0.92
Ties: 2001, 2009
Land and Ocean +0.76 ± 0.10 +1.37 ± 0.18 Warmest 4th 2010 +0.86 +1.55
Coolest 130th 1908 -0.54 -0.97
Southern Hemisphere
Land +0.44 ± 0.18 +0.79 ± 0.32 Warmest 21st 2010 +1.04 +1.87
Coolest 113rd 1917 -0.99 -1.78
Ocean +0.42 ± 0.04 +0.76 ± 0.07 Warmest 12th 1998 +0.62 +1.12
Coolest 122nd 1911 -0.54 -0.97
Ties: 1999
Land and Ocean +0.43 ± 0.07 +0.77 ± 0.13 Warmest 14th 1998 +0.67 +1.21
Coolest 120th 1911 -0.54 -0.97

Year-to-date (January–May)

January–May 2012 Blended Land and Ocean Surface Temperature Anomalies in degree CelsiusJanuary–May 2012

The globally-averaged temperature across land and oceans for the first five months of 2012 was the 11th warmest January–May on record. Of note, the year-to-date global anomalies for 2012 have increased each month as the year has progressed and La Niña conditions waned — January: +0.35°C (+0.65°F); January–February: +0.37°C (+0.67°F); January–March: +0.39°C (+0.70°F); January–April: +0.46°C (+0.83°F); and January–May (+0.50°C (+0.90°F). The record for the warmest January–May was set in 2010, with a temperature that was 0.71°C (1.28°F) above average.

2012 year to date anomalies compared with five warmest years on record
Global Year to Date Temperature Anomalies

The greatest January–May warmth was observed over southern Greenland, northern Russia, and the eastern two-thirds of North America. The coolest anomalies occurred across nearly all of Alaska, Mongolia and bordering regions, and most of Australia.

January–May Anomaly Rank
(out of 133 years)
Records
°C °F Year(s) °C °F
Global
Land +0.85 ± 0.21 +1.53 ± 0.38 Warmest 10th 2007 +1.31 +2.36
Coolest 124th 1893 -0.96 -1.73
Ocean +0.37 ± 0.04 +0.67 ± 0.07 Warmest 12th 1998, 2010 +0.56 +1.01
Coolest 122nd 1911 -0.51 -0.92
Land and Ocean +0.50 ± 0.09 +0.90 ± 0.16 Warmest 11th 2010 +0.71 +1.28
Coolest 123rd 1911 -0.51 -0.92
Northern Hemisphere
Land +0.99 ± 0.26 +1.78 ± 0.47 Warmest 9th 2007 +1.49 +2.68
Coolest 125th 1893 -1.13 -2.03
Ties: 2009
Ocean +0.35 ± 0.05 +0.63 ± 0.09 Warmest 10th 2010 +0.56 +1.01
Coolest 124th 1910, 1911 -0.47 -0.85
Ties: 2001, 2011
Land and Ocean +0.59 ± 0.13 +1.06 ± 0.23 Warmest 10th 2007 +0.85 +1.53
Coolest 124th 1893 -0.67 -1.21
Southern Hemisphere
Land +0.48 ± 0.16 +0.86 ± 0.29 Warmest 21st 2010 +1.03 +1.85
Coolest 113rd 1917 -0.91 -1.64
Ocean +0.39 ± 0.04 +0.70 ± 0.07 Warmest 15th 1998 +0.60 +1.08
Coolest 119th 1911 -0.53 -0.95
Land and Ocean +0.41 ± 0.07 +0.74 ± 0.13 Warmest 16th 1998 +0.66 +1.19
Coolest 118th 1911 -0.54 -0.97

The most current data may be accessed via the Global Surface Temperature Anomalies page.

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Images of sea surface temperature conditions are available for all weeks during 2012 from the weekly SST page.


Precipitation

The maps below represent anomaly values based on the GHCN dataset of land surface stations using a base period of 1961–1990. As is typical, precipitation anomalies during both May and March–May 2012 varied significantly around the world.

  • For only the third time since records began in 1851, two tropical storms formed in the North Atlantic hurricane basin before the official start of the hurricane season (June 1st). The storms brought beneficial rainfall to parts of the drought-stricken southeastern United States.

  • May was dry across Spain, with average precipitation that was 60 percent of the monthly average. The country's Mediterranean regions and archipelagos were the driest regions, with precipitation less than 25 percent of average. In the east, stations in Murcia and Castellon reported their driest Mays on record.

  • Much of India was drier than average for the month, as the country anticipated the onset of the southwest monsoon season in early June.

  • With the dissipation of La Niña in April, below-average precipitation fell across Australia in May, just 60 percent of the average monthly amount. The state of Western Australia reported its fifth driest May, with precipitation just 22 percent of average.

  • Average rainfall across Australia during austral autumn was 125 percent of normal, the 17th wettest such period on record. Rainfall was above average across all states, with the exception of Western Australia, which was 98 percent of average. Tasmania observed its wettest autumn since 1977, although ranked 26th wettest in its 113-year period of record.

Additional details on flooding and drought events around the world can also be found on the May 2012 Global Hazards page.

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References

Peterson, T.C. and R.S. Vose, 1997: An Overview of the Global Historical Climatology Network Database. Bull. Amer. Meteorol. Soc., 78, 2837-2849.

Quayle, R.G., T.C. Peterson, A.N. Basist, and C. S. Godfrey, 1999: An operational near-real-time global temperature index. Geophys. Res. Lett., 26, 333-335.

Smith, T.M., and R.W. Reynolds (2005), A global merged land air and sea surface temperature reconstruction based on historical observations (1880-1997), J. Clim., 18, 2021-2036.

Smith, et al (2008), Improvements to NOAA's Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006), J. Climate., 21, 2283-2293.

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Global Hazards

Please note: Material provided in this report is chosen subjectively and included at the discretion of the National Climatic Data Center (NCDC). The ability to report on a given event is limited by the amount of information available to NCDC at the time of publication. Inclusion of a particular event does not constitute a greater importance in comparison with an event that has not been incorporated into the discussion. Data included in this report are preliminary unless otherwise stated. Links to supporting information are valid at the time of publication, but they are not maintained or changed after publication.


Updated 14 June 2012


May 26thWildfires across the U.S. read more May 2012Drought plagued Brazil read more May 2ndHeavy rain triggered flash floods across Ethiopia. read more May 18thTorrential rain falls across central Cuba. read more May 10thSevere storms affected parts of northwestern China. read more May 2012Tropical Storm Alberto, Hurricane Bud, and Tropical Storm Beryl read more



Drought conditions

Large Fire Map from NIFC as of 29 May 2012
Large Fire Map from NIFC
as of 29 May 2012
Source: NIFC

A massive wildfire, triggered on May 26th by two lightning strikes, destroyed a dozen cabins and 7 small outbuildings in southwestern New Mexico and spread smoke across the state and into Arizona, prompting air-quality warnings. The wildfire, which grew due to the persistent winds, scorched nearly 85,000 acres. More than 500 firefighters battled the blaze. In southern California, a wildfire that burned through 3,100 acres from May 24th–26th prompted the evacuation of 100 homes in the Shelter Valley area and an additional 50 people from a recreational vehicle park in San Diego County. Across Nevada, a permitted burn in the Topaz Ranch Estates was rekindled by the gusty winds, spreading quickly and destroying two homes and 17 outbuildings, and scorching 7,500 acres. Please visit the U.S. Wildfires page for additional information on wildfires.

Severe drought gripped northeastern Brazil during May, the worst drought there in five decades, affecting over 1,100 towns. According to reports, the severe drought caused what is called "water wars" in rural areas, with an average of one person a day being killed in these "water wars". The water shortages have endangered the lives of local people and their livestock.

Heavy rainfall and flooding

Flash floods on May 2nd impacted Ethiopia's Somali region, causing significant damage. The flash floods damaged planted crops and stored foods in the affected areas, and claimed the lives of numerous livestock.

A low pressure system brought copious rain to northern parts of Honduras, prompting floods that caused damage to 106 homes and forced the evacuation of 500 people in the Trojes, El Paraíso municipality. Fortunately, no fatalities were reported.

Torrential rain fell across central Cuba during the week of May 18th, claiming the lives of two people, damaging or destroying nearly 1,200 homes, and forcing the evacuation of thousands of residents. According to media reports, the province of Sancti Spiritus (east of Havana) is the most affected area, with rivers and dams reaching their 98% capacity and over 8,500 people affected. More than 8,100 acres of crops were flooded, with the most important damages occurring to sugar cane fields, tobacco, and coffee.

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Severe Storms

Severe storms produced heavy downpours and dangerous hail across parts of northwestern China on May 10th. The storms were responsible for 40 fatalities and leaving 87 people with injuries and an additional 18 people missing. The storms affected more than two-thirds of the Gansu province's 450,000 residents. According to reports, homes collapsed, roads were blocked, farmlands were destroyed, and the power supply services were disrupted.

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Tropical Cyclones

Tropical Storm Alberto on 19 May 2012
Tropical Storm Alberto
19 May 2012
Source: NASA Earth Observatory

Tropical Storm Alberto formed off the coast of South Carolina and Georgia, U.S. on May 19th. Alberto was the first named Atlantic storm in the 2012 Atlantic hurricane season and the first storm to form during May—the month prior to the official start of the hurricane season—in the Atlantic basin since Tropical Storm Arthur (May 31st–June 2nd) in 2008. Alberto is also the earliest-forming tropical storm in the Atlantic basin since Tropical Storm Ana (April 20th–24th) in 2003. Although the official Atlantic hurricane season begins on June 1st, there have been a total of 18 tropical storms to have formed in May since records began in 1851. However, Alberto is one of three Atlantic tropical storms to have formed in May in over three decades. Although Alberto did not make landfall, it caused disruptions to the tourist industry as tourist cruises were cancelled. The tropical storm also prompted thunderstorms across parts of the region. Alberto dissipated on May 22nd. The East North Pacific Basin also saw its first tropical storm in the 2012 Hurricane Season, when Tropical Storm Aletta formed on May 14th. Aletta was not a threat to any land areas and did not make landfall. Aletta dissipated on May 19th. This was also the first time a tropical storm formed before the official start of the hurricane season in both the Atlantic and East Pacific basins. The official East North Pacific hurricane season begins May 15th.


Hurricane Bud on 24 May 2012
Hurricane Bud
24 May 2012
Source: NASA Earth Observatory

On May 21st, the East North Pacific recorded its second tropical storm to form during the 2012 Hurricane season. Hurricane Bud developed south of Mexico and quickly intensified to hurricane status by May 24th. The storm reached its peak intensity on May 25th, with maximum sustained winds of 115 mph (185 km/hr) which is a Category 3 hurricane. Hurricane Bud tracked towards the Mexican coast, prompting the government to prepare for the storm by closing in Colima and Jalisco Mexican states, closing the port of Manzanillo, banning swimming in the ocean in Puerto Vallarta, and opening nearly 1,000 shelters in Guerrero and Colima. The storm produced heavy downpours and waves of six feet, and strong winds knocked trees down. Bud dissipated rapidly offshore on May 26th. According to reports, Bud was the strongest East North Pacific storm on record to form so early in the year and ties with 2002 Hurricane Alma as the strongest May hurricane on record in the East North Pacific Basin, behind 2001 Hurricane Adolph.


Tropical Storm Beryl on 27 May 2012
Tropical Storm Beryl
27 May 2012
Source: NASA Earth Observatory

The second tropical storm to have formed in the 2012 Atlantic Hurricane season was Tropical Storm Beryl. Beryl formed on May 26th off the coast of South Carolina as a subtropical storm. However, by the next day the storm transitioned into a tropical cyclone. On May 27th, Beryl made landfall in northeastern Florida near Jacksonville Beach with maximum sustained winds of 70 mph (110 km/hr). Beryl became the strongest landfalling May storm since the May 1908 hurricane which had maximum sustained winds of 75 mph (120 km/hr). Beryl was also the second storm to make landfall during Memorial Day weekend in the U.S., behind the Subtropical Storm Alpha in 1972. Although Beryl ruined people's three-day vacation plans, the storm brought much-needed rain to the drought-stricken areas in the southeastern United States. Beryl also produced strong winds, causing trees to fall and downing power lines, leaving nearly 23,000 customers without electricity across northern Florida and parts of Georgia. Minor flooding was also reported in some affected areas.

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Synoptic Discussion

Note: This Synoptic Discussion describes recent weather events and climate anomalies in relation to the phenomena that cause the weather. These phenomena include the jet stream, fronts and low pressure systems that bring precipitation, high pressure systems that bring dry weather, and the mechanisms which control these features — such as El Niño, La Niña, and other oceanic and atmospheric drivers (PNA, NAO, AO, and others). The report may contain more technical language than other components of the State of the Climate series.


NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.


Synoptic Discussion

Upper-level circulation pattern and anomalies averaged for May 2012
Upper-level circulation pattern and anomalies averaged for May 2012.

The weather patternweather pattern over North America in May 2012 consisted of the seasonal battle between subtropical high pressure (Bermuda High) in the south and the jet stream (polar front) in the north. The Bermuda High brought warmer-than-normal air to much of the United States and drier-than-normal weather to western and central regions of the country. Cold fronts and low pressure systems scraped against the fringes of the Bermuda High, bringing bouts of cooler air, areas of rain, and occasional severe weather. Only the northwest corner of the country had widespread cooler-than-normal monthly averaged temperatures, courtesy of frequent upper-level troughs which, near the end of the month, brought areas of snow to parts of the Northern Rockies and Montana High Plains. But on the whole, May clocked in with below-average snow cover and tornado activity.


Did You Know?

Subtropical Highs

The sun is the ultimate source of energy that drives the earth's weather. Most of the energy reaches the equatorial regions and the least energy reaches the poles, causing the tropics to warm and the poles to cool. The earth's atmosphere redistributes this heat imbalance through a complex set of atmospheric circulation patterns. The warm air at the low latitudes rises and moves toward the poles. The rising air, and the subsequent clouds and precipitation, cause the tropics to be very wet. As the air moves towards the subtropics, it descends over the oceans and creates semi-permanent circulation features called subtropical highs. In the Northern Hemisphere, these high pressure systems are located over the North Pacific and North Atlantic oceans. The North Atlantic High is generally centered over Bermuda, so it is also known as the Bermuda High. The descending air under subtropical highs warms and dries as it descends, resulting in generally sunny skies and dry weather. Cold air from the poles flows toward lower latitudes in order to complete the redistribution of the heat imbalance in the atmosphere. This cold polar air collides with warmer subtropical air in the mid-latitudes, resulting in frontal precipitation and low pressure cyclonic storm systems.

This entire system of fronts, subtropical highs, and tropical rain migrates with the seasons, moving northward during the Northern Hemisphere summer and southward during the Northern Hemisphere winter. Sometimes during the summer, the Bermuda High will extend further to the west than usual, encompassing a significant part of the southern and eastern United States. Its descending air inhibits precipitation and its anticyclonic circulation pattern deflects tropical storms and hurricanes to the south and weakens cold fronts to its north, resulting in heat waves and droughts.

More about climate monitoring…

As seen in weekly precipitation anomaly maps (weeks 1, 2, 3, 4, 5), the migrating fronts and low pressure systems generated precipitation along two storm tracks — one in the northern tier states and one in the southern tier states along the Gulf of Mexico. Rain from Tropical Storm Beryl near the end of May brought relief from the drought in northern Florida to the coastal Carolinas. But much of the interior U.S. had below-normal monthly precipitation, with two states in the Great Basin and three in the Central Plains to Mid-Mississippi Valley ranking in the top ten driest category for the month. Five states (Minnesota, the Carolinas, New Hampshire, and Vermont) ranked in the top ten wettest category. May 2012 was the 27th driest May nationwide in the 1895-2012 record. This rainfall pattern, in combination with increased evaporation caused by above-normal temperatures, expanded drought conditions in the West, Great Plains, and Mid-Mississippi Valley. The month had significant wildfire activity in the Southwest and western Great Lakes, but total acreage burned nationally was near average. Rainfall along the Atlantic coast shrank drought areas in the Southeast and Northeast. By May 29, moderate to exceptional drought expanded to cover 53 percent of the West, 43 percent of the South, and 32 percent of the Central and Northern Plains, according to the U.S. Drought Monitor. On a national scale, however, drought coverage shrank slightly, to 37 percent of the contiguous United States, due in large part to contraction in the Northeast and Southeast.

With the Bermuda High extending its seasonal reach into the U.S., and with warm southerly winds blowing northward ahead of the cool fronts, above-normal temperatures dominated much of the country for much of the month (weeks 1, 2, 3, 4, 5), resulting in the second warmest May in the 1895-2012 record. The unusual warmth is reflected in the daily temperature records, with more than five times as many record warm highs and lows occurring than record cold highs and lows. About 3200 daily high temperature records and over 3400 record warm daily low temperatures were tied or broken. In comparison, beneath the migrating upper-level troughs and associated cold fronts, only about 430 record low temperatures and about 700 record cool daily high temperatures were tied or broken. (These numbers are preliminary and are expected to increase as more data arrive.) Twenty-six states, from Colorado to New England, ranked in the top ten warmest category for May. The national Residential Energy Demand Temperature Index (REDTI) for May 2012 was the 47th lowest May value in the 1895-2012 record, indicating that the anomalous warmth reduced heating demands in the typically-cool (this time of year) North and introduced or increased demand for cooling in the South. When the above-normal temperatures of the past several months are factored in, the national REDTI value was lowest on record for the last three months (March-May 2012), year-to-date (January-May 2012), and last six months (December 2011-May 2012).

When averaged together, the mixture of temperature and precipitation extremes gave the U.S. (as noted above) the second warmest and 27th driest May in the 118-year record. Averaging extremes tends to cancel them out. But when extremes are combined cumulatively, like in the U.S. Climate Extremes Index (CEI), they may tell a different story. The large spatial extent of unusually warm highs (second largest), unusually warm lows (fourth largest), and very dry conditions (tenth largest) gave the U.S. its eighth largest CEI for May. The combination of persistent and unusual warmth, drought, and extreme daily precipitation events over the last several months, however, contributed to the highest national CEI for the last three months (March-May), year-to-date (January-May), and last 12 months (June-May), and the second highest CEI for the last six months (December-May). Several regions also had the highest regional CEI for the last 3, 6, and 12 months and year-to-date. Concurrent with these high CEI values are the record warm temperature ranks for the nation for March-May 2012, January-May 2012, December 2011-May 2012, and June 2011-May 2012.

Cold fronts and low pressure systems moving in the storm track flow are influenced by the broadscale atmospheric circulation. Four such large-scale atmospheric circulation drivers were potentially influential during May:

Map of monthly temperature anomalies Map of monthly precipitation anomalies

Upper-level circulation pattern and anomalies averaged for March-May 2012
Upper-level circulation pattern and anomalies averaged for March-May 2012.

The boundaries between positive and negative anomalies are shifted slightly, but the March-May 2012 averaged upper-level circulation anomalies are generally consistent with a positive AO pattern across the Lower 48 States, North Atlantic, and North Pacific. The above-normal heights over the eastern U.S. are shifted north reflecting a stronger Bermuda High, with below-normal heights over western North America (May 2012 and March-May 2012) coinciding with below-normal sea surface temperatures in the northeastern North Pacific. The pattern of observed temperature anomalies for May 2012 and the last three months (March-May) corresponds to the positive phase of the AO and negative phase of the PNA across most of the country. The May 2012 and March-May precipitation patterns also correspond to a positive AO and a negative PNA where the correlations exist. As noted above, most of the indices were near neutral values for much of the month. When the atmospheric circulation drivers are neutral or in a state of transition, their influence becomes difficult to trace and can be overwhelmed by other competing forces, including random fluctuations in the atmosphere.

Tornadoes

NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.

Updated: 7 June 2012

The values in this report are preliminary, and the final counts and results will change as tornado events are investigated and confirmed. This month’s report will not be updated with final statistics. For final information please visit the following sites:



According to data from the Storm Prediction Center, the count of preliminary tornado reports during May — 139 — was much below the 1991-2010 average of 276. May is typically the most active tornado month during the year. This marks the slowest May, in terms of the number of tornadoes since 2005, when 124 tornadoes were confirmed. Once the final tornado count is confirmed, it is likely the May 2012 count will be revised lower. There were no tornado-related fatalities reported during the month, the first time since 2005. The largest outbreak of the month occurred across south Texas on May 10th, when there were 20 preliminary tornado reports, with only minimal damage reported.

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Hurricanes & Tropical Storms

NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.


Note: This report catalogs recent tropical cyclones and places each basin's tropical cyclone activity in a climate-scale context. It is not updated in real time. Users seeking real time status and forecasts of tropical cyclones should visit The National Hurricane Center.

East North Pacific Basin

Aletta
Tropical Storm Aletta Satellite Image
Aletta Track
Tropical Storm Aletta Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Aletta
Cyclogenesis Date 05/15
Cyclolysis Date 05/17
Highest Saffir-Simpson Category TS
Maximum 6-hr Sustained Wind 46 mph (40 kt or 74 km/h)
Min Pressure 1005 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 1.1775 x 104
Landfall Information (date, location and sustained winds)
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

Bud
Hurricane Bud Satellite Image
Bud Track
Hurricane Bud Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Bud
Cyclogenesis Date 05/22
Cyclolysis Date 05/26
Highest Saffir-Simpson Category Cat 3
Maximum 6-hr Sustained Wind 115 mph (100 kt or 185 km/h)
Min Pressure 960 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 7.5100 x 104
Landfall Information (date, location and sustained winds)
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

Atlantic Basin

Tropical Storm Alberto formed as a tropical depression on May 19th off the North and South Carolina coast along a stationary front. The storm quickly strengthened into a tropical storm with sustained winds of 50 miles per hour. The storm moved to the northeast, just off the coast of the Carolinas, never making landfall. The storm weakened to a tropical depression on the morning of the 22nd, and became extra-tropical after moving over colder water and experiencing strong wind shear. Alberto was an unusual storm because it formed before the official start of the North Atlantic’s tropical cyclone season for the North Atlantic, which begins on June 1st. Alberto was the first named storm during May since tropical storm Arthur in 2008. Only 27 known tropical cyclones, prior to Alberto, had reached tropical storm status before June since 1851.

Alberto
Tropical Storm Alberto Satellite Image


Alberto Track
Tropical Storm Alberto Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Alberto
Cyclogenesis Date 05/19
Cyclolysis Date 05/21
Highest Saffir-Simpson Category TS
Maximum 6-hr Sustained Wind 58 mph (50 kt or 93 km/h)
Min Pressure 995 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 1.4225 x 104
Landfall Information (date, location and sustained winds)
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

Beryl formed as a subtropical storm off the coast of the Carolinas on May 25th. As the storm moved westward it strengthened and gained more tropical characteristics and became a tropical storm on May 27th, with sustained winds of 70 miles per hour. On May 28th, the storm made landfall near Jacksonville, Florida. Beryl quickly weakened as it moved over northern Florida and into southern Georgia. The tropical depression then moved to the northeast and off the North Carolina Coast, where it was declared extra-tropical. Heavy rainfall was the main impact of Beryl, but the rain was a welcome sight as much of the region had been experiencing drought conditions for over a year. Beryl was another unusual storm, with respect to how early in the year it formed. Beryl marked only the third time that a second tropical cyclone reached tropical storm strength in the North Atlantic since records began in 1851, joining 1908 and 1887. Beryl was also only the eighth tropical storm to make landfall in the U.S. during May.

Beryl
Tropical Storm Beryl Satellite Image


Beryl Track
Tropical Storm Beryl Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Beryl
Cyclogenesis Date 05/26
Cyclolysis Date 05/28
Highest Saffir-Simpson Category TS
Maximum 6-hr Sustained Wind 69 mph (60 kt or 111 km/h)
Min Pressure 992 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 2.1600 x 104
Landfall Information (date, location and sustained winds) 05/27–near Jackson Beach, Florida (60 kt or 111 km/h)
05/25–05/30 Total Precip (map)
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

West North Pacific Basin

Sanvu
Tropical Storm Sanvu Satellite Image
Sanvu Track
Tropical Storm Sanvu Forecast Track


Safir Simpson Color Legend for Track Map from Unisys
Saffir-Simpson Scale Color Legend
Tropical Cyclone Summary
Tropical Cyclone Sanvu
Cyclogenesis Date 05/21
Cyclolysis Date 05/27
Highest Saffir-Simpson Category Cat 1
Maximum 6-hr Sustained Wind 92 mph (80 kt or 148 km/h)
Min Pressure 975 mbar
Accumulated Cyclone Energy (ACE*) Index (kt2) 8.9150 x 104
Landfall Information (date, location and sustained winds)
Deaths 0
*The (ACE) Index calculations are based on preliminary data.

Drought

NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.

Issued 14 June 2012
Contents Of This Report:
Map showing Palmer Z Index

National Drought Overview

[top]


Detailed Drought Discussion

Overview

May 2012 was another warmer- and drier-than-average month (2nd warmest and 27th driest May on record, based on data back to 1895) when weather conditions are averaged across the country. Warm anomalies dominated at the monthly level and most weeks (weeks 1, 2, 3, 4, 5). Migrating fronts and low pressure systems generated precipitation along two storm tracks — one in the northern tier states and one in the southern tier states along the Gulf of Mexico — as seen in the precipitation pattern on the monthly scale as well as a weekly basis (weeks 1, 2, 3, 4, 5), with persistent dryness occurring across the interior U.S. between the tracks. Rain from Tropical Storm Beryl near the end of May brought relief from the drought in northern Florida to the coastal Carolinas, while above-normal rainfall shrank drought areas in the Northeast. Dry weather, in combination with increased evaporation caused by above-normal temperatures, expanded drought conditions in the West, Great Plains, and Mid-Mississippi Valley, while below-normal rainfall worsened drought conditions in Hawaii. Nationally, the moderate-to-exceptional (D1-D4) drought footprint decreased to about 31 percent of the country while the percentage in the abnormally dry to exceptional drought category increased to about 54 percent.

The U.S. Drought Monitor drought map valid May 29, 2012
The U.S. Drought Monitor drought map valid May 29, 2012.

By the end of the month, the core drought areas in the U.S. included:

  • a large area of moderate (D1) to exceptional (D4) drought in the Southeast;
  • moderate to extreme (D3) drought in the Southern Plains spreading into the Southwest, with a few pockets of exceptional drought lingering in west Texas;
  • moderate to extreme drought in the Southwest, with moderate to severe (D2) drought stretching to the West Coast and into the Pacific Northwest;
  • pockets of moderate to severe drought lingering in the Mid-Atlantic and Northeast states, but limited to mainly along the coast;
  • areas of moderate to severe drought scattered across the Midwest and Central to Northern Plains; and
  • parts of the central and southern islands of Hawaii, where moderate to extreme drought persisted.

Palmer Drought Index

The Palmer drought indices measure the balance between moisture demand (evapotranspiration driven by temperature) and moisture supply (precipitation). The Palmer Z Index depicts moisture conditions for the current month, while the Palmer Hydrological Drought Index (PHDI) and Palmer Drought Severity Index (PDSI) depict the current month's cumulative moisture conditions integrated over the last several months.

Palmer Z Index map Palmer Hydrological Drought Index map

As seen on the May 2012 Palmer Z Index map, low precipitation and warm temperatures (with the accompanying increased evapotranspiration) led to short-term drought across much of the Southwest and Intermountain Basin, across the Central and Southern Plains, and into the Midwest and eastern Great Lakes this month. Wet conditions are evident on the Z Index map in scattered areas along the East Coast, Upper Mississippi Valley, and extreme northern and southern High Plains. Compared with the April 2012 PHDI map, the May 2012 PHDI map indicates that drought conditions improved in the Southeast and Upper Mississippi Valley, but intensified in parts of the West and Mid-Mississippi Valley to Midwest. The May 2012 PHDI map also reflects the long-term nature of the drought conditions. The Z Index and PHDI maps in combination show that precipitation brought relief to parts of the Southeast and Upper Mississippi Valley drought areas, but for much of the Southwest to Mid-Mississippi Valley — it was drier than normal over the existing drought areas.

Precipitation minus Potential Evapotranspiration for May 2012 calculated using the Palmer Model
Precipitation minus Potential Evapotranspiration for May 2012 calculated using the Palmer Model.

The Palmer model assesses the supply of water versus the atmospheric demand for water by computing evapotranspiration. Precipitation is used to measure water supply, while the Thornthwaite equations are used to compute potential evapotranspiration (the amount of water that would be evaporated and transpired by plants) based on temperature. In the model, if the amount of precipitation (P) during the month is greater than the potential evapotranspiration (PET) for the month, then the leftover P soaks into the ground to recharge soil moisture, and any left over after that runs off as streamflow. If P is less than PET, then moisture has to be drawn out of the soil to meet the PET demand. Hotter temperatures result in greater PET which requires more P just to meet the greater demand. During May 2012, temperatures were much above normal across much of the country, resulting in PET values which exceeded four inches from the Southern Plains to Mid-Atlantic Coast. Precipitation amounts were well below normalless than four inches across a large part of the Southern Plains to Midwest — resulting in P minus PET values which went strongly negative and sapped soil moisture reserves, stressed crops and other vegetation, and shrank streams. Even if normal precipitation amounts had occurred, it would not have been enough to meet PET demand in many areas.


Standardized Precipitation Index

The Standardized Precipitation Index (SPI) measures moisture supply. The SPI maps here show the spatial extent of anomalously wet and dry areas at time scales ranging from 1 month to 24 months.

1-month Standardized Precipitation Index 3-month Standardized Precipitation Index 6-month Standardized Precipitation Index

Recent precipitation (May and March) has countered dryness in the short-term (1-, 2-, 3-month SPI) along parts of the coastal Southeast drought areas, but dry conditions are evident at all time scales beginning at 2 months for the interior Southeast, and 12 months for the coast, out to 24 months. Similarly, beneficial May rains reduced the dry footprint in the Northeast to the 3- to 6-month time frames. Dryness was reasserting itself over much of the Southern Plains at the 1- and 2-month time scales, but the most severe dryness here is evident at the 12- to 24-month time scales where dry conditions stretch from the Southwest to Southeast. Parts of the Northwest and Northern Rockies have dryness indicated at the 1-, 9-, and 12-month time scales, but are generally wet from 2 to 6 months and at 24 months. The rest of the West is generally dry at all time scales from 1 to 12 months. Widespread dryness from California to the Mid-Mississippi Valley is most evident from 1 to 3 months, but is also suggested at 6 months.


9-month Standardized Precipitation Index 12-month Standardized Precipitation Index 24-month Standardized Precipitation Index

Agricultural and Hydrological Indices and Impacts

USDA topsoil moisture short to very short
USDA topsoil moisture short to very short
USGS monthly streamflow percentiles
USGS monthly streamflow percentiles

Drought conditions were reflected in numerous agricultural, hydrological, and other meteorological indicators, both observed and modeled:

hydrological:

USDA western U.S. mountain snow water content anomaly map
USDA western U.S. mountain snow water content anomaly map.

agricultural:

Map showing VegDRI (Vegetation Drought Response Index)
Map showing VegDRI (Vegetation Drought Response Index).

meteorological:

Map showing maximum consecutive number of days with no precipitation
Map showing maximum consecutive number of days with no precipitation.

Regional Discussion

May 2012 was drier than normal for most of the stations in the Hawaiian Islands, resulting in an expansion of D1-D3 (moderate to extreme drought) and D0 (abnormally dry conditions) this month compared to last month. Longer-term conditions continued drier than normal (last 2, 3, 6, 12, 24, 36 months, year to date [January-present], and water year to date [October-present]), especially for the southern islands. As noted by the NWS, drought impacts continued in many areas.

In Alaska, May 2012 was generally drier than normal in the southwest areas and wetter than normal elsewhere. Precipitation deficits are evident at some interior stations at short time scales (2 - 3 months, year to date) and at long time scales (24 and 36 months) but not at the time scales in between (6 and 12 months and water year to date). Snow water content (stations, basins) was below normal at interior locations and above normal in southern coastal locations, although this is nearing the end of the snowpack season with some interior locations having less than six inches of snow on the ground. There was no drought or abnormal dryness indicated on the May 29th USDM map.

The rainfall pattern across Puerto Rico during May was generally mixed. An area of drier-than-normal conditions is evident in a small southeastern area at most time scales (2, 3, 6 months, year to date, and water year to date). With streamflow above average, the May 29th USDM map had no drought or abnormally dry areas on the island.

Current month state precipitation ranks 3-month state precipitation ranks

On a statewide basis, May 2012 ranked in the top ten driest Mays for two states in the West (Utah at fourth driest and Nevada at sixth driest) and three in the Central Plains to Mid-Mississippi Valley (Arkansas at second driest, Kansas at fourth driest, and Missouri at seventh driest). Eleven other states from the West to Midwest ranked in the driest third of the historical record. Two large areas of dryness stand out at the three month time scale — one centered in the Central Rockies and the other in the Ohio Valley — with a smaller area along the Mid-Atlantic to Northeast coast. Colorado (fourth driest), Wyoming (fourth driest), and Utah (fifth driest) in the West, Indiana (eighth driest) in the Midwest, and Delaware (fifth driest) in the East ranked in the top ten driest category for May, while 16 other states fell in the driest third of the historical record.

Year-to-date state precipitation ranks 6-month state precipitation ranks

12-month state precipitation ranks

Dryness for the year to date is even more severe in the Mid-Atlantic to Northeast coastal area, with Delaware having the driest January-May in the 1895-2012 record and three other states ranking in the top ten driest category. Four states in the West (Arizona, Colorado, Utah, and Wyoming) turned in the tenth driest, or drier, year-to-date. Seventeen other states in the West, Midwest, Southeast, and Northeast ranked in the driest third of the historical record. If the time period is extended another month back to include December, the dryness is not as severe in the East and Midwest, but is more evident in the Far West. Five states had the tenth driest, or drier, December-May while 15 other states ranked in the driest third of the historical record. At the 12-month time scale, dryness dominates in the southern states while the Northeast is wet. June 2011-May 2012 ranked in the top ten driest category for Georgia (sixth driest) and Nevada (eighth driest). Thirteen other states ranked in the driest third of the historical record.

Georgia had the lowest PHDI in the 1900-2012 record for May, reflecting the cumulative severity of the dryness over the last three years. But when all months of the year (not just May) are considered, the 1920s and 1950s had months with a drier PHDI. Georgia statewide PHDI, May, 1900-2012

Percent area of the Western U.S. in moderate to extreme drought, based on the Palmer Drought Index
Percent area of the Western U.S. in moderate to extreme drought, based on the Palmer Drought Index.

With the Pacific storm track near the Canadian border and a secondary storm track along the Gulf of Mexico coast, much of the western U.S. was left with little significant precipitation this month. Drier-than-normal weather has dominated from the Southwest and intermountain basin to the Central and Southern Rockies for the water year to date (October-present), as reflected in low elevation as well as high elevation (SNOTEL) precipitation, especially for the southern half of the West. Mountain snow water equivalent (basin averages as well as station percent of normal and percentiles) were near to above normal in the Washington Cascades and extreme Northern Rockies, but elsewhere conditions were drier. Low precipitation as well as above-normal temperatures, which accelerated melting, contributed to the low snowpack, especially in the southern areas. Mountain snowpack is a crucial water supply during the following melt season. Fortunately, the reservoirs in most states were near to above normal, with New Mexico and Oregon averaging below normal statewide. According to the USDM, 53 percent of the West was experiencing moderate to exceptional drought at the end of May, an 8 percent increase compared to April. The Palmer Drought Index statistic was about 56 percent, reflecting a remarkable rise over the last five months.

A more detailed drought discussion, provided by the NOAA Regional Climate Centers and others, can be found below.

SoutheastSouthMidwestNortheastHigh Plains
WestUpper Colorado River BasinPacific Islands

As noted by the Southeast Regional Climate Center, mean temperatures in May were generally above average across the Southeast region while monthly precipitation totals were variable. Much of this variability was due to the passage of Tropical Storm Beryl, which dropped between 2 and 7 inches (50.8 and 177.8 mm) of rain across large parts of northeast Florida and eastern sections of Georgia, the Carolinas, and extreme southeastern Virginia, and as much as 10 inches (254 mm) of rain across central portions of the Florida Panhandle, from the 28th to the 31st of the month. This contributed to monthly precipitation totals that ranged between 150 and 300 percent of normal. In addition, several locations across central North Carolina and Virginia, southern Alabama, and south Florida also exhibited above normal precipitation for the month. Conversely, much of the interior of the Southeast remained dry in May, with monthly precipitation generally less than 50 percent of normal. Monthly precipitation was near normal across most of Puerto Rico and the U.S. Virgin Islands.

The rainfall from Tropical Storm Beryl helped alleviate drought conditions across eastern sections of the Southeast. Improvements of one to two drought categories in the USDM were noted across parts of the Florida Panhandle, southeastern Georgia, and the coastal plain of the Carolinas. Although the rainfall from Beryl helped extinguish several fires across northern Florida, an estimated 60 fires were still active across 10,000 acres (40.5 sq km) of the state at the end of the month. Crop damage due to hail was reported across several counties in Georgia, including several hundreds of acres of watermelon and other crops that were approaching harvest. The warm, dry weather that persisted across much of the Southeast this spring resulted in reduced wheat yields across Florida, while peach volumes were down between 25 and 35 percent across Georgia due to a lack of accumulated chill hours. On the other hand, several vegetable and commodity crops were able to ship early due to favorable weather conditions.

As explained by the Southern Regional Climate Center, as was the case in the past few months, the Southern region experienced yet another warmer than normal month in May. With the exception of southwestern Texas, May 2012 was a rather dry month for the bulk of the region. Precipitation was scarce in the central portions of the region where most stations recorded less than one fourth of the normal monthly totals. This was also the case for most of the Texas and Oklahoma panhandle region. Elsewhere, values ranged mostly between twenty-five and fifty percent of normal. Southwestern Texas was the only portion of the region that observed above normal rainfall, with precipitation totals ranging from one and one half to four times of normal. Despite that, Texas' statewide precipitation average was slightly on the dry side with a total of 2.81 inches (71.37 mm). Arkansas, Oklahoma and Louisiana had the highest statewide precipitation rankings. For Oklahoma, which received a total of 2.33 inches (59.18 mm), it was the eleventh driest May on record (1895-2012). It was the second driest May on record in Arkansas, which saw only 1.63 inches (41.40 mm) of precipitation. Louisiana averaged 2.26 inches (57.40 mm) of precipitation, which makes it their fifteenth driest May on record (1895-2012). For Mississippi, it was the thirty-third driest May on record, which is based on a statewide precipitation total of 3.05 inches (77.47 mm). Lastly, Tennessee experienced its twenty-eighth driest May on record, with a statewide precipitation total of 3.26 inches (82.80 mm).

Consistent dryness over much of the Southern region has led to an expansion of drought in some areas, while above average precipitation has led to improvements in other areas. In the case of the latter, high precipitation in southwestern Texas has led to the removal of all exception drought in that portion of the state. Though moderate drought remains, this is a significant improvement over last month, where most of the area was riddled with severe to extreme drought. In northern Arkansas, where precipitation was below normal for much of the month, there has been an introduction of moderate drought. This also includes portions of northeastern Mississippi and western Tennessee, where conditions were also drier than normal over the past several weeks.

As summarized by the Midwest Regional Climate Center, May precipitation varied with much of the northern third of the Midwest recording above normal precipitation including a large swath of Minnesota that received two to three times normal. The southeast parts of the Midwest were close to normal while much of Missouri, Illinois, Indiana, southern Michigan, and southeast Iowa received only 25 to 75 percent of normal. Spring precipitation was also heaviest across Minnesota with totals ranging from 150 to 200 percent of normal. The driest areas for spring extended from northwest Ohio into Illinois. May temperatures were above normal across the Midwest, with all nine Midwest states recording above-normal temperatures for the last seven months or more.

Drought in Minnesota and northwest Iowa eased with May rains running two to three times normal. Other Midwest locations saw drought worsen as lack of rain, combined with enhanced evapotranspiration, dried out the upper soil layers. Drought conditions worsened in northwest Minnesota and for most of the southern two-thirds of the Midwest. Severe Drought was limited to western Kentucky, extreme southern Illinois, and the boot heel of Missouri but many areas saw drying of the topsoil, stressed plants, and dry lawns as concerns increased about the potential for drought to rapidly worsen. The many days of dry conditions in the Midwest allowed farmers to spend more time in the fields, thus corn and soybean planting was running ahead of normal. With much of the crop in the ground by the end of the month, farmers were hoping for adequate rains to replenish soil moisture and supply needed water to stressed plants going into the hot summer months.

As noted by the Northeast Regional Climate Center, May 2012 was the 14th consecutive warmer-than-normal month in the Northeast, with each of the states averaging on the warm side of normal. It was the warmest May since 1991 for the region and the 5th warmest since 1895. Temperature averages for the spring (March-May) of 2012 were also above normal.

After three months of below normal precipitation totals, the Northeast averaged 118 percent of normal in May. Precipitation was not evenly distributed — New Hampshire's total was 157 percent of normal, while Delaware's was only 49 percent of May's normal monthly total. For the 118 years of record, New Hampshire ranked 7th wettest, Vermont 9th, and Pennsylvania, 22nd, while Delaware ranked 24th driest. Spring 2012 precipitation totals averaged below normal in the Northeast (91 percent) and in nine of the twelve states in the region. March through May departures among the drier-than-normal states ranged from 56 percent in Delaware to 98 percent in New Hampshire. State and regional precipitation totals for the January through May time period were all below normal. The Northeast average was 87 percent of normal and state departures ranged from 97 percent in West Virginia to 49 percent in Delaware. It was the driest January through May since 1895 in Delaware, the 3rd driest in Connecticut, the 6th driest in Maryland, and the 10th driest in New Jersey.

Rainfall during the month resulted in fewer areas of abnormally dry (D0), moderate drought (D1) and severe drought (D2) in the region. The May 29th USDM still had moderate (D1) and severe (D2) drought in Delaware, with pockets of D1 drought in Connecticut, Maryland and Massachusetts. New Jersey, most of New Hampshire and southeastern Maine improved from D1 drought to D0 at month's end.

As explained by the High Plains Regional Climate Center, May 2012 was largely warm and dry across the High Plains region. The largest temperature departures occurred in southern portions of the region, where the departures from normal temperature ranged from 4.0-8.0 degrees F (2.2-4.4 degrees C) above normal. The only areas in the region to have lower than normal temperatures were central and western North Dakota and pockets of Wyoming and South Dakota. Many locations across the region were ranked in the top 10 warmest Mays on record. This spring (March, April, and May) was a record breaker across the entire High Plains region. Average temperatures were above normal at all locations in the region and the largest temperature departures occurred in the east as areas of South Dakota, Nebraska, and Kansas had average temperatures which were over 8.0 degrees F (4.4 degrees C) above normal.

May 2012 was dry for much of the High Plains region. A large area encompassing southern Wyoming, western and southern Nebraska, northern and western Kansas, and the east and west sides of Colorado had precipitation totals which were less than 50 percent of normal. In addition, many locations within that area received only 25 percent or less of normal precipitation and ranked in the top 10 driest Mays on record. Goodland, Kansas had its second driest May on record with only 0.45 inch (11 mm) of precipitation, which was 13 percent of normal precipitation (period of record 1895-2012). The 1927 record held at 0.31 inch (8 mm). Snowpack in Colorado and Wyoming continued to decline. According to the Natural Resources Conservation Service, by the end of the month, the statewide snowpack was just 5 percent of average in Colorado and 22 percent of average in Wyoming. According to the Denver Post, the low snowpack has raised concerns about potential impacts on river recreation in Colorado. Although the majority of the region was drier than normal, a few areas had above normal precipitation totals including eastern South Dakota, northeastern Nebraska, south-central Colorado, and a few pockets of North Dakota and Wyoming.

Spring (March, April, and May) precipitation and snowfall totals were some of the lowest on record in the western part of the High Plains region. A large area of the region had precipitation totals which were 25-50 percent of normal including southern Wyoming, the panhandle of Nebraska, and western and northern Colorado. Some examples of the dryness include Cheyenne, Wyoming and Boulder, Colorado. Cheyenne had its second driest spring on record with only 0.69 inch (18 mm) of liquid equivalent precipitation. This was not far off from the record 0.67 inch (17 mm) which was set in the spring of 1880 (period of record 1871-2012). In addition, Cheyenne had its least snowy spring on record with only 0.6 inch (2 cm) of snowfall. This beat the old record of 3.5 inches (9 cm) which occurred in 2007 (snowfall period of record 1883-2012). Similarly, Boulder, Colorado had its third driest spring with 3.10 inches (79 mm) of precipitation. The record 2.21 inches (56 mm) which fell in 1925 was able to hold on (period of record 1893-2012). Boulder also had its least snowy spring on record with a mere 1.6 inches (4 cm) of snowfall. This easily beat the old record of 3.5 inches (9 cm) which fell in 1982 and was incredibly lower than the average spring snowfall, which in Boulder is 29.5 inches (75 cm).

According to the National Agricultural Statistics Service, the earliest start to the wheat harvest in Kansas since records began in 1952 occurred this year. By the end of the month, at least 4 percent of the wheat harvest was complete. The earliest harvest prior to this year occurred in 1962 when 1 percent of the crop had been harvested by June 2nd. The dry, hot, and windy weather in Nebraska led to low soil moisture which caused producers to turn on pivots to aid in crop germination.

There were many changes again to the USDM this month. Improvements were made in eastern South Dakota and Nebraska as drought conditions were eliminated due to ample precipitation. Only small areas of abnormally dry conditions (D0) remained there. Moderate drought conditions (D1) were erased from western South Dakota and the majority of western North Dakota as well. Unfortunately, drought conditions elsewhere either emerged or worsened over the course of the month. D1 conditions in eastern North Dakota expanded towards the south. New D0 and patches of D1 emerged across Kansas. D1 conditions also expanded further across southern Colorado and also across the panhandle of Nebraska and into southern Wyoming and northwestern Colorado. The big story this month was the development of extreme drought conditions (D3) in northwestern Colorado due to extremely low precipitation.

As summarized by the Western Regional Climate Center, May is typically a month in which temperatures increase and precipitation totals have begun to wane in the coastal and southern West as the Pacific storm track edges northward and the Southwest Monsoon system has yet to develop. May 2012 showed few exceptions to this trend. Many Southwest locations received no precipitation at all, and only a smattering of stations in the Northwest and along the Mexico border recorded average to above-average precipitation. The northern tier of the region experienced cooler than normal average temperatures this month, while in the Southwest, average temperatures were generally above the May mean. Critical fire conditions (low relative humidity, high wind, drought conditions) dominated the Southwest, leading to the rapid development of several large wild land fires and New Mexico experiencing its largest fire on record.

Many locations the Southwest were dry this month, not uncommon in past Mays. For the 31st time in the last 75 years, Las Vegas, Nevada received no measureable precipitation (less than 0.01 in / 0.25 mm) in May. Further west, Santa Barbara, California has 25 years in its 71-year record with no measurable May precipitation. Other zero-precipitation locations this month include Yuma and Flagstaff, Arizona and Palm Springs, California. To the north, central Washington and Oregon have seen drought development over the last few months. This month, Spokane, Washington received only 0.69 in (17.5 mm) rainfall, the 28th driest May in the station's 112-year record.

Temperatures in the Northwest and along the coast this month were 2-4 F (1-2 C) below normal, similar to but less cool than May 2010 and 2011. Average May temperatures do not show recent warming or cooling in the Northwest, though the past two years were anomalously cool. The Southwest saw temperatures 2-6 F (1-3 C) above normal, breaking the cool May pattern of 2010 and 2011, and back to the general trend of increasing May temperatures in the Southwest over the past 30 years.

A significant consequence of the continued warm and dry March, April, and May has been a drastic lowering of the expected summer snowmelt in the Intermountain West. Forecasts of Colorado River inflow to Lake Powell have dropped very far, and now rank among the 3rd or 4th lowest in the past century.

Upper Colorado River Basin: As reported by the Colorado Climate Center, the May 29th NIDIS (National Integrated Drought Information System) assessment for the Upper Colorado River Basin (UCRB) indicated that, water-year-to-date (WYTD) SNOTEL precipitation percentiles were lowest for the Yampa and Gunnison basins in Colorado, with many sites reporting in the lowest 5th percentile or below. The Wasatch range in Utah and the northern mountains of Colorado were also dry, with most precipitation percentiles in the teens. SNOTEL percentiles in the Upper Green basin in Wyoming were generally above the 40th percentile. In the San Juan basin, a few SNOTEL percentiles remained above the 30th percentile, but there were many SNOTEL sites reporting below the 30th percentile. Snowpack conditions around the UCRB were all well below average and many sites have completely melted out. This is a combined result of less than average seasonal snowpack accumulations and much earlier melting. For example, accumulated snow water equivalent around the Colorado headwaters peaked over a month earlier than average. Accumulations were similar to 2002 accumulations and melting has occurred earlier than 2002. This is similar for many of the sub-basins in the UCRB. As of May 27th, about 78 percent of the stream gages in the basin were recording below normal flows. All of the reservoirs above Lake Powell were currently near or above their May storage averages. Flaming Gorge, Blue Mesa, and Navajo have seen volume decreases since the beginning of the month. The other reservoirs have seen slight increases, though they were observing volume increases much less than what is normally expected for this time of year. Lake Powell was at 79 percent of average and 64 percent of capacity. Daily inflows into the major reservoirs in the basin were much below average for this time of year.

Pacific Islands: According to reports from National Weather Service offices, the Pacific ENSO Applications Climate Center (PEAC), and partners, conditions varied across the Pacific Islands.

As noted by the National Weather Service office in Honolulu, the 2012 dry season has started hard and fast, especially in most of the leeward areas of the state where may rainfall totals came in below average. An existing area of extreme drought, or the D3 category in the USDM map, spread from the south Kohala district and the Pohakuloa region of the Hamakua district into the north-facing slopes of Hualalai in the north Kona district. Severe drought, or D2 category conditions, covered the lower elevations of southwestern Kau and portions of the Humuula Saddle. In Maui County, extreme drought conditions have persisted over western Molokai and southwest Maui from Kihei to Makena. Severe drought covered the island of Lanai, the lower leeward slopes of the west Maui mountains and leeward Haleakala from Kula to Kaupo. Kauai and Oahu have remained drought-free. However, leeward areas were drying out and vegetation growth from the wet season has recently started to burn in a few areas.

Some drought impacts in Hawaii include the following:

  • On Kauai, there were no drought impacts to report. However, agriculture impacts beyond the usual seasonal dryness will begin to appear if lower than normal rainfall persists.
  • On Oahu, the water supply in the Waimanalo reservoir remains above pre-drought levels. On April 23, the state Department of Agriculture rescinded the mandatory 10 percent water use restriction from the Waimanalo reservoir. A voluntary 10 percent reduction in water use has taken its place as a precaution for the dry season.
  • On Molokai, the water level in the Kualapuu reservoir remains very low. Thus, the State of Hawaii Department of Agriculture has continued a mandatory 30 percent reduction in irrigation water consumption.
  • On Lanai, no significant change since the May 3 update. Pastures and general vegetation conditions have been very poor.
  • On Maui, pastures and general vegetation in leeward Maui remain extremely dry and there is an increasing risk for significant brush fires in the area. A rancher operating near Kaupo reported that springs have been drying up. Earlier, an upcountry rancher indicated that over the past four years, poor pasture conditions have resulted in reduced cattle weights, poor breeding rates due to a significant reduction in the number of breeding cows and losses in the hundreds of thousands of dollars. The Maui County Department of Water Supply has continued to call for a 5 percent reduction in water use for upcountry residents. The request for a 10 percent reduction in water use by central and south Maui also remained in effect.
  • On the Big Island, pastures and general vegetation over most of the south Kohala district and portions of the north Kona district along the north-facing slopes of Hualalai were in very poor condition. There is an increasing risk of significant brush fires in these areas. Earlier reports indicated that there was little or no edible forage for livestock. Ranchers in these areas have already destocked cattle and water hauling operations have been ongoing for many months.

SPI values for seven time periods for Hawaiian Island stations, computed by the Honolulu NWS office.
SPI values for seven time periods for Hawaiian Island stations

On other Pacific Islands (maps — Micronesia, Marshall Islands, basinwide), May was drier than normal for Kosrae and Majuro, but near to above normal for the rest of the stations. Total rainfall for the last 12 months (June 2011-May 2012) was near to above normal for all stations.

Pacific Island Percent of Normal* Precipitation
Station Name** Jun 2011 Jul 2011 Aug 2011 Sep 2011 Oct 2011 Nov 2011 Dec 2011 Jan 2012 Feb 2011 Mar 2012 Apr 2012 May 2012 Jun 2011-May 2012
Chuuk 218% 125% 144% 118% 97% 136% 125% 57% 181% 107% 40% 173% 126%
Guam IAP 96% 203% 102% 129% 135% 83% 103% 162% 94% 215% 121% 224% 132%
Kapingamarangi 130% 147% 162% 107% 57% 81% 124% 109% 71% 121% 102% 143% 115%
Koror 129% 152% 155% 266% 122% 62% 97% 36% 126% 121% 120% 122% 129%
Kosrae 114% 87% 122% 104% 154% 95% 174% 65% 185% 60% 84% 86% 108%
Kwajalein 121% 104% 144% 111% 125% 130% 84% 134% 114% 84% 68% 161% 118%
Majuro 97% 131% 108% 115% 115% 119% 91% 107% 65% 194% 97% 59% 107%
Pago Pago 132% 42% 72% 29% 137% 157% 75% 61% 98% 131% 90% 126% 98%
Pohnpei 128% 92% 138% 115% 77% 123% 110% 82% 138% 98% 45% 115% 103%
Saipan 174% 96% 93% 68% 140% 57% 110% 77% 183% 35% 33% 166% 101%
Yap 113% 138% 129% 156% 101% 112% 116% 33% 117% 185% 89% 142% 122%
* 1981-2010 Normal Median Precipitation
** Clicking on the station name will reveal a climatology graph of the normal monthly rainfall.

SPI values for seven time periods for Pacific Islands, computed by the Honolulu NWS office.
SPI values for seven time periods for Pacific Islands

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State/Regional/National Moisture Status
A detailed review of drought and moisture conditions is available for all contiguous U.S. states, the nine standard regions, and the nation (contiguous U.S.):

States
alabama arizona arkansas california colorado connecticut
delaware florida georgia idaho illinois indiana
iowa kansas kentucky louisiana maine maryland
massachusetts michigan minnesota mississippi missouri montana
nebraska nevada new hampshire new jersey new mexico new york
north carolina north dakota ohio oklahoma oregon pennsylvania
rhode island south carolina south dakota tennessee texas utah
vermont virginia washington west virginia wisconsin wyoming

Regional
northeast u. s. east north central u. s. central u. s.
southeast u. s. west north central u. s. south u. s.
southwest u. s. northwest u. s. west u. s.

National
Contiguous United States

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Drought Indicators
The following indicators illustrate the drought conditions this month:

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Contacts & Questions
For additional, or more localized, drought information, please visit:

Global Snow & Ice

NH Snow Cover Extent

Data were provided by the Global Snow Laboratory, Rutgers University. Period of record is 1967-2012 (46 years).

The Northern Hemisphere snow cover extent (SCE) during May 2012 was much below average and ranked as the second smallest May SCE in the 46-year satellite period of record. The monthly SCE was 3.47 million square km below the long-term average of 19.4 million square km (7.5 million square miles). This marks the eighth consecutive May with below-average May snow cover for the Northern Hemisphere. Both the Eurasian and North American land areas had below-average snow coverage for the month. For the spring period (March-May), the Northern Hemisphere SCE was 1.9 million square km (735,000 square miles) below average, ranking as the sixth smallest spring snow extent on record. This is the ninth consecutive spring with below-average spring snow cover for the hemisphere.

During May 2012, the North American SCE was nearly 0.8 million square km (310,000 square miles) below average, ranking as the eighth smallest May SCE on record. According to analysis by Rutgers Global Snow Lab, the mountainous West of the U.S. had below-average snow cover during May, as well as most of eastern and central Canada. Above-average snow cover was observed across the Canadian Rockies and southern Alaska. For spring (March-May), the North American SCE was the third smallest on record, 0.9 million square km (0.35 million square miles) below average.

Eurasian SCE during May 2012 was 2.67 million square km (1.0 million square miles) below average, the smallest May snow extent on record for the continent. This is in sharp contrast to February 2012, when the Eurasian SCE was the third largest for the month. A warm spring led to rapid snow melt across much of the continent. According to analysis by Rutgers Global Snow Lab, below-average snow cover was observed across the Alps, most of Russia, the Himalayas, and northwestern China. Above-average snow cover was present for Scandinavia and parts of the Tibetan Plateau. For the spring season (March-May), the Eurasian SCE was nearly 1.0 million square km (386,000 square miles) below average, the 12th smallest spring SCE on record for the continent.

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Sea Ice Extent

According to the National Snow and Ice Data Center (NSIDC), the Northern Hemisphere sea ice extent — which is measured onboard NOAA satellites — averaged for May 2012 was 13.13 million square km (5.07 million square miles), 3.46 percent below average. This ranked as the 12th smallest (23rd largest) May sea ice extent on record for the Northern Hemisphere in the 1979-2012 period of record. May 2012 is the 11th consecutive May and the 132nd consecutive month with below-average Arctic sea ice extent. May Arctic sea ice extent has decreased at an average rate of 2.3 percent per decade.

According to the analysis by the NSIDC, sea ice coverage remained above-average across the Bering Sea, similar to the winter and early spring season. The extensive ice in the Bering was countered by below-average ice in the Barents and Kara Seas, resulting in the overall Arctic ice extent being below average. By the end of May, open ocean areas had started to develop along the Arctic coast of Canada. The NSIDC noted that spring Arctic ice extents are not necessarily indicative of ice conditions during summer.

The May 2012 Southern Hemisphere sea ice extent was 10.95 million square km (4.2 million square miles), 2.38 percent above average, and the 15th largest (20th smallest) May extent in the 1979-2012 period of record. Southern Hemisphere sea ice extent was above-average during the first half of May, but trended closer to average in the second half of the month. Antarctic sea ice extent has increased at an average rate of 2.1 percent per decade, with substantial interannual variability.

For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page.

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Upper Air

Troposphere

Lower Troposphere

May Lower Troposphere
May Anomaly Rank
(out of 34 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH +0.29 +0.52 Coolest 31st 1985 -0.33 -0.59 +0.11 +0.20
Warmest 4th 1998 +0.57 +1.03
RSS +0.15 +0.27 Coolest 28th 1985 -0.41 -0.74 +0.12 +0.21
Warmest 7th 1998 +0.58 +1.04
March-May Lower Troposphere
March–
May
Anomaly Rank
(out of 34 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH +0.23 +0.41 Coolest 30th 1993 -0.34 -0.61 +0.13 +0.23
Warmest 5th 1998 +0.55 +0.99
RSS +0.11 +0.20 Coolest 26th 1985 -0.41 -0.74 +0.13 +0.23
Warmest 9th 1998 +0.60 +1.08
Year-to-Date Lower Troposphere
January–
May
Anomaly Rank
(out of 34 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH +0.10 +0.18 Coolest 25th 1993 -0.33 -0.59 +0.12 +0.22
Warmest 10th 1998 +0.56 +1.01
RSS -0.02 -0.04 Coolest 17th 1985 -0.40 -0.72 +0.12 +0.22
Warmest 17th 1998 +0.57 +1.03
Ties: 1981

Mid-troposphere

May Mid-troposphere
May Anomaly Rank
(out of 34 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH +0.10 +0.18 Coolest 27th 1989 -0.33 -0.59 +0.04 +0.06
Warmest 8th 1998 +0.58 +1.04
RSS +0.04 +0.07 Coolest 21st 1989 -0.32 -0.58 +0.06 +0.10
Warmest 14th 1998 +0.60 +1.08
UW-UAH +0.18 +0.32 Coolest 27th 1989 -0.41 -0.74 +0.09 +0.16
Warmest 8th 1998 +0.67 +1.21
UW-RSS +0.19 +0.34 Coolest 30th 1989 -0.37 -0.67 +0.10 +0.19
Warmest 5th 1998 +0.68 +1.22
March-May Mid-troposphere
March–
May
Anomaly Rank
(out of 34 years*)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH +0.06 +0.11 Coolest 22nd 1993 -0.32 -0.58 +0.03 +0.05
Warmest 13th 1998 +0.58 +1.04
RSS +0.03 +0.05 Coolest 21st 1993 -0.33 -0.59 +0.06 +0.12
Warmest 13th 1998 +0.58 +1.04
Ties: 1990
UW-UAH +0.14 +0.25 Coolest 27th 1993 -0.39 -0.70 +0.09 +0.15
Warmest 7th 1998 +0.67 +1.21
Ties: 2007
UW-RSS +0.14 +0.25 Coolest 26th 1993 -0.39 -0.70 +0.12 +0.21
Warmest 9th 1998 +0.65 +1.17
RATPAC* +0.14 +0.25 Coolest 47th 1965 -0.93 -1.67 +0.14 +0.25
Warmest 9th 1998 +0.58 +1.04

*RATPAC rank is based on 55 years of data

Year-to-Date Mid-troposphere
January–
May
Anomaly Rank
(out of 34 years*)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH -0.06 -0.11 Coolest 14th 1993, 1989 -0.28 -0.50 +0.02 +0.04
Warmest 20th 1998 +0.57 +1.03
Ties: 1982
RSS -0.07 -0.13 Coolest 15th 1993, 1989 -0.30 -0.54 +0.07 +0.12
Warmest 20th 1998 +0.56 +1.01
UW-UAH 0.00 0.00 Coolest 17th 1993 -0.36 -0.65 +0.08 +0.14
Warmest 18th 1998 +0.66 +1.19
RATPAC* -0.03 -0.05 Coolest 37th 1965 -0.91 -1.64 +0.14 +0.25
Warmest 18th 2010 +0.66 +1.19
Ties: 1980

*RATPAC rank is based on 55 years of data

Stratosphere

May Stratosphere
May Anomaly Rank
(out of 34 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH -0.45 -0.81 Coolest 3rd 2011 -0.65 -1.17 -0.34 -0.62
Warmest 31st 1992 +0.92 +1.66
Ties: 1996
RSS -0.42 -0.76 Coolest 2nd 2011 -0.60 -1.08 -0.26 -0.47
Warmest 33rd 1992 +0.89 +1.60
March-May Stratosphere
March–
May
Anomaly Rank
(out of 34 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH -0.49 -0.88 Coolest 1st 2012 -0.49 -0.88 -0.34 -0.61
Warmest 34th 1983 +1.05 +1.89
RSS -0.48 -0.86 Coolest 1st 2012 -0.48 -0.86 -0.27 -0.49
Warmest 34th 1992 +1.02 +1.84
Year-to-Date Stratosphere
January–
May
Anomaly Rank
(out of 34 years)
Record Years Decadal Trend
°C °F Year °C °F °C °F
UAH -0.50 -0.90 Coolest 1st 2012 -0.50 -0.90 -0.35 -0.64
Warmest 34th 1983 +1.18 +2.12
RSS -0.51 -0.92 Coolest 1st 2012 -0.51 -0.92 -0.30 -0.53
Warmest 34th 1983 +1.09 +1.96

Background Information

Temperatures above the Earth's surface are measured within the lower troposphere, middle troposphere, and stratosphere using in-situ balloon-borne instruments (radiosondes) and polar-orbiting satellites (NOAA's TIROS-N). The radiosonde and satellite records have been adjusted to remove time-dependent biases (artificialities caused by changes in radiosonde instruments and measurement practices as well as changes in satellite instruments and orbital features through time). Global averages from radiosonde data are available from 1958 to present, while satellite measurements date back to 1979.

The mid-troposphere temperatures are centered in the in the atmospheric layer approximately 3–10 km [2–6 miles] above the Earth's surface, which also includes a portion of the lower stratosphere. (The Microwave Sounding Unit [MSU] channel used to measure mid-tropospheric temperatures receives about 25 percent of its signal above 10 km [6 miles].) Because the stratosphere has cooled due to increasing greenhouse gases in the troposphere and losses of ozone in the stratosphere, the stratospheric contribution to the tropospheric average, as measured from satellites, creates an artificial component of cooling to the mid-troposphere temperatures. The University of Washington (UW) versions of the UAH and RSS analyses attempt to remove the stratospheric influence from the mid-troposphere measurements, and as a result the UW versions tend to have a larger warming trend than either the UAH or RSS versions. For additional information, please see NCDC's Microwave Sounding Unit page.

The radiosonde data used in this global analysis were developed using the Lanzante, Klein, Seidel (2003) ("LKS") bias-adjusted dataset and the First Difference Method (Free et al. 2004) (RATPAC). Additional details are available. Satellite data have been adjusted by the Global Hydrology and Climate Center at the University of Alabama in Huntsville (UAH). An independent analysis is also performed by Remote Sensing Systems (RSS) and a third analysis has been performed by Dr. Qiang Fu of the University of Washington (UW) (Fu et al. 2004)** to remove the influence of the stratosphere on the mid-troposphere value. Global averages from radiosonde data are available from 1958 to present, while satellite measurements began in 1979.

References

Wildfires

Updated: 7 June 2012


Overview

During May, wildfire activity across the U.S. was below average, although warm and dry conditions occurred across a large portion of the country. The 337,182 acres which burned in May was slightly below average, and the 4,435 fires was the least amount on record for the month. Despite the slow wildfire activity, several large wildfires had significant impacts in Arizona, New Mexico, and Michigan.

1-Month Wildfire Statistics*
May Totals Rank
(out of 13 years)
Record 2000-2010
Average
Value Year
Acres Burned 337,182 6ᵗʰ Most 1,069,997 2011 340,608
8ᵗʰ Least
Number of Fires 4,435 13ᵗʰ Most 18,469 2001 9,509
Least on Record
Acres Burned per Fire 76.0 3ʳᵈ Most 161.5 2011 37.2
11ᵗʰ Least
3-Month Wildfire Statistics*
March–May Totals Rank
(out of 13 years)
Record 2000-2010
Average
Value Year
Acres Burned 618,015 9ᵗʰ Most 3,246,509 2011 924,820
5ᵗʰ Least
Number of Fires 17,295 13ᵗʰ Most 35,909 2006 26,835
Least on Record
Acres Burned per Fire 35.7 7ᵗʰ Most 161.5 2011 33.3
7ᵗʰ Least
Year-to-Date Wildfire Statistics*
January–May Totals Rank
(out of 13 years)
Record 2000-2010
Average
Value Year
Acres Burned 710,661 9ᵗʰ Most 3,450,882 2011 1,059,751
5ᵗʰ Least
Number of Fires 22,292 12ᵗʰ Most 41,845 2006 32,407
2ⁿᵈ Least
Acres Burned per Fire 31.9 7ᵗʰ Most 115.6 2011 31.5
7ᵗʰ Least

*Data Source: The National Interagency Fire Center (NIFC)

Discussion

As a whole, the contiguous U.S. had its 2nd warmest May on record, with warmer-than-average conditions engulfing the eastern two-thirds of the contiguous U.S. and the Southwest. Only the Pacific Northwest and Northern Rockies had near-average temperatures. Precipitation totals were mixed during May, with the Eastern Seaboard and the Upper Midwest being wetter than average. Dry conditions were present from the Southwest, stretching into the Central Plains, and into the Mid-South. Please see the U.S. temperature and precipitation report for additional information. According to the U.S. Drought Monitor, the percent area of the contiguous U.S. experiencing Moderate-to-Exceptional (D1-D4) drought shrank slightly from 38.18 percent to 37.37 percent during May. Drought conditions improved for the Mid-Atlantic and Northeast, where several storm systems brought beneficial rainfall. Drought improved by one to two categories across the Southeast, where Tropical Storm Beryl brought beneficial rainfall to northern Florida and southern Georgia. Drought developed across the Mid-South, but conditions improved across the Upper Midwest. Rainfall across western Texas and eastern New Mexico nearly eradicated the ongoing Exceptional Drought in the Southern Plains. Drought conditions persisted and worsened slightly across much of the Southwest and central Rockies.

Significant Events


The Upper Peninsula of Michigan experienced an usually warm and dry spring, on the heels of a relatively dry winter, creating ideal wildfire conditions. The Pine Creek Fire and the Duck Lake Fire were ignited by a lightning strike on May 20th. and both quickly grew out of control due to strong winds. The fires were fully contained by the end of May, but after charring over 3,400 acres. The largest impact of the fires was the diminished air quality across the Upper Peninsula, as well as southern Ontario.

Two large wildfires burned in Arizona during the middle of May, in the mountains north of Phoenix. The Gladiator Fire began on May 13th by a structural fire on private property, and by May 16th had prompted an evacuation order for the historic mining community of Crown King. By the end of May, the fire had charred over 16,200 acres and was only 45 percent contained. The Sunflower Fire was ignited on May 12th from unknown causes and by the end of May had burned over 17,600 acres and was 80 percent contained. The Sunflower Fire was burning in a rural area and posed no threat to any communities.

Two large wildfires which began in mid-May in New Mexico, the Baldy Fire and the White Water Fire, merged to create the Whitewater-Baldy Fire complex. Both fires were ignited by lightning strikes in the very dry Gila National Forest in western New Mexico. By June 1st, the complex burned over 216,650 acres and was only ten percent contained, with very high growth potential. The amount of smoke from the fire was unusually high due to the dense coniferous forests which were impacted, causing very low air quality conditions across a large area of western New Mexico. The fire surpassed the Las Conchas Fire of 2011, which destroyed over 156,500 acres, as the largest fire in New Mexico history.

Monthly Wildfire Conditions

Wildfire information and environmental conditions are provided by the National Interagency Fire Center (NIFC) and the U.S. Forest Service (USFS) Wildland Fire Assessment System (WFAS).

At the beginning of May, there were seven large wildfires burning across the nation. Two fires were active in Florida, where ongoing drought conditions contributed to high KBDI values. One fire was active in eastern Texas, which was experiencing low 10-hour fuel moistures. Four fires were burning in the west, one in west Texas, two in Arizona, and one in Nevada, where dry conditions the previous month during April led to high fire danger, low 10-hour, 100-hour, and 1,000-hour fuel moistures, as well as very high KBDI values.

On May 31st, there were nine large wildfires burning nationwide. Six large wildfires were active across the Southwest in California, Arizona, New Mexico, and Colorado, where drought conditions persisted or worsened for many locations during the month. Low 10-hour, 100-hour, and 1,000-hour fuel moistures as well as very high KBDI values and high fire danger were observed across the region. Two large fires were active across the Upper Peninsula of Michigan, associated with the Pine Creek Fire complex, where low 10-hour fuel moistures were present. One additional fire was burning in southern Florida, where relatively high KBDI values were observed.


All Fire Related Maps


Citing This Report

NOAA National Climatic Data Center, State of the Climate for May 2012, published online June 2012, retrieved on April 16, 2014 from http://www.ncdc.noaa.gov/sotc/2012/5.