State of the Climate - April 2012
Maps and Graphics
Temperature and Precipitation Ranks
U.S. Percentage Areas
Supplemental April and January-April Information
- Year-to-date temperature evolution for select U.S. cities
- Statewide and regional temperature departures from average
- Supplemental year-to-date precipitation grahics
- All-time April warm daily maximum temperature records
- Ten warmest 12-month periods for the contiguous U.S.
- Climate Highlights — April
- Warmer-than-average temperatures engulfed much of the contiguous United States during April, and the nationally-averaged temperature was 55.7 degrees F, 3.6 degrees F above average — the third warmest on record. The precipitation averaged across the nation was 2.23 inches, 0.20 inch below average.
- Warmer-than-average temperatures were present for a large portion of the nation during April — six states in the central U.S. and three states in the Northeast had April temperatures ranking among their ten warmest. Above-average temperatures were also present for the Southeast, Upper Midwest, and much of the West. No state in the contiguous United States had April temperatures that were below average.
- April 2012 came on the heels of the warmest March on record for the Lower-48, and eight states — Illinois, Indiana, Kentucky, Michigan, Wisconsin,Ohio, Pennsylvania, and West Virginia — had April temperatures which were, despite being warmer than normal, were still not as warm as their March temperatures.
- Statewide precipitation totals were mixed during April, with wetter-than-average conditions across the West Coast and Northern and Central Plains. Oregon had its seventh wettest April on record. Drier-than-average conditions were present from Texas, along the Gulf Coast, stretching northward into the Great Lakes. Tennessee had its sixth driest April on record, while Alabama had its eighth driest.
- The warmer-than-average conditions, which have persisted for several months, limited snowfall over a large portion of the country. According to the Rutgers Global Snow Lab, the April snow cover extent across the contiguous United States was the third smallest on record, despite the late season Nor’easter which impacted the Northeast near the end of April.
- According to NOAA’s Storm Prediction Center, there were 228 preliminary tornado reports during April, which is above average. The majority of the tornadoes occurred during an April 14th outbreak across the Central Plains. However, tornado activity during April 2012 paled in comparison to April 2011, when over 750 tornadoes wreaked havoc across the Southeast, causing significant damage and loss of life.
- A list of select April temperature and precipitation records can be found here.
- Year-to-Date (January-April)
- January-April 2012 was the warmest such period on record for the contiguous United States, with an average temperature of 45.4 degrees F, 5.4 degrees F above the long-term average. Twenty-six states, all east of the Rockies, were record warm for the four-month period, and an additional 17 states had temperatures for the period among their ten warmest.
- The first four months of 2012 were drier than average for the contiguous United States as a whole, with some regional variability. The eastern third of the nation was drier than average, where Maryland and Delaware were record dry, and an additional six states had precipitation totals ranking among the ten driest. Drier-than-average conditions were also present for much of the Interior West.
- Wetter-than-average conditions occurred across the central regions of the country and the Pacific Northwest, where the above-average precipitation contributed to higher than normal mountain snowpack at the end of the snow season. The amount of snowpack at this time of year is important in determining the water supply for the region during the upcoming summer period.
- According to the U.S. Drought Monitor, as of May 1st, 38.2 percent of the contiguous United States was experiencing drought conditions, an increase from the 31.9 percent at the beginning of 2012. Drought worsened across the Northeast, Southeast, and the interior West, while beneficial precipitation significantly improved drought conditions across the Southern Plains and western Gulf of Mexico.
- The U.S. Climate Extremes Index (USCEI), an index that tracks the highest and lowest 10 percent of extremes in temperature, precipitation, drought and tropical cyclones across the contiguous U.S., was a record 42 percent during the January-April period, over twice the average value. Extremes in warm daytime temperatures (82 percent) and warm nighttime temperatures (68 percent) covered a large area of the nation, contributing to the record high value.
- 12-month period (May 2011-April 2012)
- The 12-month period (May 2011-April 2012), which includes several warm periods for the country — second hottest summer, fourth warmest winter, and warmest March — was the warmest consecutive 12-month period for the contiguous United States. Twenty-two states were record warm for the 12-month period, and an additional 19 states were top ten warm. The 12-month running average temperature for the contiguous U.S. was 55.7 degrees F, which is 2.8 degrees F above the 20th century average.
Alaska Temperature and Precipitation:
- Alaska had its 26th warmest April since records began in 1918, with a temperature 2.2°F (1.2°C) above the 1971–2000 average.
- Alaska had its 41st warmest February-April since records began in 1918, with a temperature 0.2°F (0.1°C) above the 1971–2000 average.
- Alaska had its 14th coolest January-April since records began in 1918, with a temperature 3.4°F (1.9°C) below the 1971–2000 average.
- Alaska had its 45th wettest April since records began in 1918, with an anomaly that was 0.1 percent above the 1971–2000 average.
- Alaska had its 34th wettest February-April since records began in 1918, with an anomaly that was 17.2 percent above the 1971–2000 average.
- Alaska had its 42nd wettest January-April since records began in 1918, with an anomaly that was 9.7 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.
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)
- The Northeast’s average temperature was 46.8 degrees F (8.2 degrees C) in April. This was only 0.6 degrees F (0.3 degrees C) warmer than normal the average this month was the closest to normal since August 2011 when the departure was +0.5 degrees F (0.3 degrees C). It was the first month since October 2011 that all the states in the region did not average warmer than normal. Maryland, New York, Pennsylvania and West Virginia ended the month cooler than normal. April’s temperature departures ranged from 0.3 degrees F (0.2 degrees C) below normal in West Virginia to 2.7 degrees F (1.5 degrees C) above normal in New Hampshire. It was the 5th warmest April since 1895 in Rhode Island, the 9th warmest in Maine and New Hampshire and the 14th warmest in Connecticut. It was the warmest year-to-date (January through April) in the Northeast and in all the states in the region except Maine, Pennsylvania, and West Virginia. Those three states had their 3rd warmest January through April since 1895.
- Precipitation totals averaged below normal for the third consecutive month. April’s regional total of 2.95 inches (74.9 cm) was 81 percent of normal. Maine was the sole state to average wetter than normal and had a departure of 121 percent. Departures among the drier-than-normal states ranged from 91 percent in Vermont to 55 percent in Pennsylvania, where it was the 16th driest April in 118 years. It was the driest January through April since 1895 in Delaware and Maryland, the 2nd driest in Connecticut and New Jersey, and the 5th driest in New Hampshire and the Northeast.
- Four consecutive dry and warm months worsened the drought conditions in parts of the Northeast. As of April 24, 2012, the U.S. Drought Monitor had much of the eastern third of the region in moderate (D1) to severe (D2) drought. A few locations in Massachusetts had implemented mandatory or voluntary outdoor water use restrictions during the month. The agricultural community in Delaware and eastern Maryland was also impacted by the dry weather some farmers have waited to plant crops due to low soil moisture while others have been irrigating a practice not typically needed during the spring. An increase in brush fires throughout the region prompted bans on outdoor burning. One fire in southeastern New York destroyed 30 buildings and spread over 50 acres at a former Catskill resort.
- A late season Nor’easter brought up to 3 inches (76.2 mm) of much needed rain to eastern New England on the 23rd, easing drought concerns there, but also dumped heavy wet snow on parts of western NY, north central and southwestern PA, and the eastern West Virginia mountains. For some locations, including Ithaca, NY with 6.0 inches (15.2 cm), it was the greatest one-day snow total of the 2011-2012 snow season. The snow fell on trees already leafed out due to the warm temperatures this spring, breaking limbs, toppling trees, and downing power lines. At least 50,000 customers in the Northeast were without power due to the storm.
- Midwest Region: (Information provided by the Midwest Regional Climate Center)
- April temperatures were near normal in the eastern part of the Midwest and above normal in the western parts of the region. Departures were within 2 degrees F (1 C) of normal for most of Ohio, Michigan, Indiana, and Wisconsin and increased to the west with temperatures 3 to 5 degrees F (2 to 3 C) above normal along the western edge of the region. Typically, temperatures warm from March to April by about 10 to 15 degrees F (6 to 9 C) but April 2012 was about the same or cooler than March 2012 for most of the Midwest. The month to month change ranged from +2 degrees F (+1 C) to -3 degrees F (-2 C) for most of the Midwest with warming of 2 to 5 degree F (1 to 3 C) in southwest Missouri, northwest Iowa, most of Minnesota, and small parts of Wisconsin and Michigan. Selected Midwest cities that recorded cooler April temperatures versus March included Dubuque, Iowa, Milwaukee, Wisconsin, Chicago, Illinois, Detroit, Michigan, Cleveland, Ohio, Cincinnati, Ohio, Indianapolis, Indiana, and St. Louis, Missouri. In Dubuque, Iowa, 2012 was the first time in 162 years that April was cooler than March. The majority of the April temperature records were record highs in the first four days of the month with record lows peaking in the last week of the month.
- April precipitation varied with above normal precipitation in most of the western half of the Midwest and below normal precipitation in the southeastern half of the region. Totals exceeded 150 percent of normal in parts of Minnesota, Missouri, and Illinois while totals failed to reach 50 percent of normal further to the south and east, including parts of Missouri, Illinois, Kentucky, Indiana, Ohio, and Michigan. April snows were recorded in the northern parts of Minnesota, Wisconsin, Michigan, and Ohio with only north central Minnesota topping normal for the month. Though the total Midwest area in drought shrank slightly in April, the locations affected spread into parts of Illinois and Kentucky.
- Several April freezes affected much of the Midwest, sparing only parts of Missouri and locations along the Mississippi and Ohio rivers. Though the timing of the freezes was not unusual, record warmth in March led to many plants having unusually early growth. Though farmers held off on planting corn and soybeans to meet crop insurance guidelines for freeze coverage, damage was widespread to fruit trees, grape vines, and winter wheat crops. With good weather to prepare fields earlier in the spring, rapid planting of corn occurred once the insurance guideline for each state was reached. Corn plantings reached 70 percent or more complete in Illinois, Indiana, Kentucky, and Missouri by the end of April compared to 5-year averages in the 20 to 45 percent range for those states.
- Severe weather in April touched seven of the nine states in the region, sparing Wisconsin and Michigan, and was blamed for two deaths. An outbreak of severe weather on the Great Plains April 14th extended across southern Iowa with seven reported tornadoes in the state. Thurman, Iowa in Freemont County was reported 75 percent destroyed by an EF2 tornado but there were no major injuries. A strong low pressure system tracked northeast on the 15th through the 17th, brought snow to the upper Midwest, set off severe thunderstorms along a trailing cold front, and led to wind advisories for much of the region as winds gusted to 55 miles per hour (90 km per hour) knocking out power to nearly 250,000 customers in Michigan alone. The strong winds on the 16th felled a tree on a van in Van Buren County, Michigan causing one death. Another death, along with five serious injuries, occurred on the 28th when severe storms swept through downtown St. Louis, Missouri. The sudden, strong winds collapsed and blew away a beer tent at a downtown venue, with nearly 200 people in the tent at that time. To the east, hail stones in Washington County, Illinois were reported to reach 4.50 inches (over 11 cm), wind gusts in Indiana reached 90 miles per hour (150 km per hour), and thousands lost power in Kentucky.
- 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 April were generally above average across the Southeast region. The greatest departures were found across Alabama, Georgia, South Carolina, eastern sections of North Carolina and Virginia, and northern Florida, where monthly temperatures were 2 to 4 degrees F (1.1 to 2.2 degrees C) above average. Temperatures across much of Virginia, North Carolina, South Florida, as well as Puerto Rico and the U.S. Virgin Islands, were near average (within 1 degree F or 0.5 degrees C) for the month. Interestingly, a few stations in the region were cooler in April than they were in March, including Lynchburg, VA, Raleigh, NC, and Dulles Airport near Washington D.C. The warm temperatures from March extended into the first week of April, as more than 250 daily maximum temperature records were tied or broken from the 1st to the 5th of the month. Temperatures reached 90 degrees F (32.2 degrees C) in the upstate of South Carolina and 80 degrees F (26.7 degrees C) across central Virginia. The warm weather this spring led to the earliest last freeze on record at Charlottesville, VA, which occurred on March 11 (period of record: 119 years). This is a week earlier than the previous record, which last occurred in 1929. Frost and freeze conditions were reported across Virginia and the Carolinas as well as at some locations across northern Alabama and Georgia on the 12th and 13th of the month as high pressure from Canada overspread much of the eastern U.S. More chilly temperatures were recorded in the wake of a strong cyclone moving up the eastern seaboard from the 22nd to the 24th of the month. Over 140 daily low maximum and over 70 daily minimum temperature records were tied or broken during this period, mostly across Alabama and Florida.
- Monthly precipitation was below average across most of the Southeast in April. In particular, the southern tier of the region (except for South Florida), as well as eastern portions of North Carolina and northern Virginia, recorded less than 50 percent of normal precipitation for the month. The driest locations were found across central portions of Alabama and Georgia, where monthly precipitation totals were less than 25 percent of normal. Columbus, GA recorded 0.49 inches (12.5 mm) of precipitation for the month, making it the 2nd driest April in a record extending back to 1948. In contrast, the wettest locations were found across western North Carolina and south Florida, where monthly precipitation was at least 150 percent and 200 percent of normal, respectively. Brevard, NC recorded 6.4 inches (162.6 mm) of precipitation on the 19th of the month, which broke the previous monthly 24-hr rainfall total of 3.7 inches (93.9 mm) (period of record: 110 years). For the month, Miami, FL recorded 7.85 inches (199.4 mm) of precipitation (250 percent of normal), while Duck Key, FL recorded 9.73 inches (247.1 mm). A strong coastal cyclone contributed to widespread precipitation totals of 2 to 3 inches (50.8 to 76.2 mm) across far eastern sections of North Carolina and Virginia from the 22nd to the 23rd of the month. This system also contributed up to 2 inches (50.8 mm) of snowfall along the higher elevations of western North Carolina. Monthly precipitation was 50 to 100 percent of normal across the interior of Puerto Rico, but as much as 200 percent of normal along the southern and eastern slopes.
- There were 171 reports of severe weather across the Southeast in April. The only confirmed tornado was a waterspout that moved onshore near Naples, FL on the 6th of the month. Several small trees and power lines were blown down, resulting in an EF-0 rating. Many reports of hail and damaging thunderstorm winds were found across central Alabama, western North Carolina, and along the North Carolina-South Carolina border. High wind reports were also scattered across Georgia and along the eastern Florida Peninsula. Crop damage from hail and high wind were reported across parts of southern Georgia. Overall, it was a much quieter month in terms of severe weather compared to last April, when the Southeast recorded a record 1,877 severe weather reports.
- Drought conditions continued to worsen across the Southeast in April. One notable exception was south Florida, which saw an elimination of drought conditions due to the heavy rains there. The area of exceptional drought (D4) expanded across southeast Alabama, southern Georgia, and into the northeast Panhandle of Florida, while the area of extreme drought (D3) expanded into South Carolina and central Florida. Areas of severe drought (D2) expanded into southeast Virginia, while moderate drought (D1) conditions re-emerged across northern sections of Alabama and Georgia. The warm, dry weather contributed to several large wildfires, including one that burned over 35,000 acres near the Florida-Georgia border and impacted air quality from the northeast Florida Panhandle all the way to the Tampa Bay area. Warm temperatures and lack of precipitation over the past six months continued to reduce stream flow and groundwater levels across parts of the Southeast, particularly southern Georgia where most gauge stations were in the bottom 10 percent or at their record low level by the end of April. Conversely, the warm weather resulted in Florida watermelons shipping as much as 2 weeks early with larger volumes than last year. The cold weather at the beginning and end of the month caused damage to the apple, blueberry, and blackberry crops in western North Carolina, with projected losses exceeding 40 percent. The cold weather also caused damage to the Bermuda grass that had begun to emerge across northern Georgia.
- 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)
- The High Plains Region was warm again this month. Similar to March, based on preliminary data, every station in the Region had above normal temperatures. Monthly temperature departures of 4.0-6.0 degrees F (1.1-3.3 degrees C) above normal were widespread across the Region and areas where temperature departures were 6.0-8.0 degrees F (3.3-4.4 degrees C) above normal included central and eastern Colorado, central and northeastern Wyoming, western South Dakota, the panhandle of Nebraska, and southeastern Kansas. The warmth caused numerous locations to be ranked in the top 10 warmest Aprils on record. Wichita, Kansas had its 5th warmest April on record with an average temperature of 62.5 degrees F (16.9 degrees C) which was 7.2 degrees F (4.0 degrees C) above normal (period of record 1888-2012). The record from 1981 and 1896 stood at 63.7 degrees F (17.6 degrees C). The warm conditions this spring allowed for planting progress, especially of corn, to be ahead of schedule throughout the Region. Going into April, there were concerns in the southern portion of the Region about the possibility of freeze damage as the average last freeze date is around mid-April to early May. While freezing temperatures did occur, only slight freeze damage was reported. Aside from agriculture, plant development in general was ahead of schedule. In southeast Nebraska, for instance, roses and peonies were blooming about 5 weeks ahead of schedule.
- Precipitation varied across the Region this month. Much of the eastern half of the Region had precipitation totals which were higher than normal, while lower than normal precipitation areas included most of Wyoming, the western half of Colorado, central and northeastern Kansas, and isolated pockets in Nebraska and the Dakotas. Most of the above normal precipitation locations ranged from 125-200 percent of normal, but there were pockets of 200-400 percent of normal precipitation that occurred in east-central Colorado, west-central Nebraska, east-central South Dakota, and southeastern North Dakota. Although monthly records were not broken, there were some daily precipitation records and most of these occurred in the middle and at the end of the month. The severe storms of April 14th were accompanied by heavy rainfall of 2-3 inches (51-76 mm) across portions of northern Kansas, Nebraska, and eastern South Dakota. April 30th was extremely wet in southern Kansas, near the Oklahoma border. Take, for instance, Parsons 2 NW, Kansas which received 5.35 inches (136 mm) of precipitation on that day. This one-day precipitation total was more than what Parsons usually gets in the entire month of April (normal April precipitation is 3.82 inches (97 mm)). This also completely crushed the old daily record of 2.68 inches (68 mm) which was set in 1954 (period of record 1925-2012). Snowfall was sparse this month and due to the continued warmth, snow pack has declined in the mountainous portions of the Region. According to the Natural Resources Conservation Service, by the end of the month, the statewide snowpack was 19 percent of average in Colorado and 45 percent of average in Wyoming. The low snowpack has raised concerns about irrigation water availability for the growing season. In addition, according to the Denver Post, Independence Pass was scheduled to open two weeks ahead of schedule because of the lack of snow in the mountains. The pass usually opens the Thursday before Memorial Day weekend. There were many changes again to the U.S. Drought Monitor this month. The drought conditions in the areas near the Colorado-Kansas border have continued to improve as all extreme drought conditions (D3) have been erased and only a couple of small areas of severe drought conditions (D2) remain. In eastern South Dakota, D2 was downgraded to moderate drought conditions (D1) and some drought conditions were completely eliminated in the northwest portion of the state. Although recent rains have led to improvements in these areas, others have seen degradation. The small area of D2 in western Colorado has expanded to include much of the west-central portion of the state. A patch of D1 that was in western South Dakota has been extended north into North Dakota and south into the panhandle of Nebraska. Abnormally dry conditions (D0) were also expanded to include eastern Wyoming and small areas of D1 have also crept into southern portions of the state. According to the U.S. Seasonal Drought outlook released on April 19th, drought conditions were expected to improve in areas of the Dakotas and eastern Nebraska. Drought conditions elsewhere in the High Plains Region were expected to persist or develop.
- April was an active severe weather month across the High Plains Region. Severe weather was reported somewhere in the Region on 15 days and resulted in a total of 396 reports (tornadoes, high winds, and large hail). The most notable severe weather day was the April 14th severe weather outbreak which brought high winds, large hail, flash flooding, and tornadoes, some of which were long-tracked, to the Region. The severe weather started in the morning and lasted until the early hours of April 15th. Ultimately, at least 50 tornadoes, ranging in strength from EF0-EF4, were confirmed.
- For more information, please go to the High Plains Regional Climate Center Home Page.
- Southern Region: (Information provided by the Southern Regional Climate Center)
- Like March, April was generally a warmer than normal month for the Southern Region. For the most part, temperatures averaged between 2 and 4 degrees F (1.11 and 2.22 degrees C) above expected values. The highest anomalies occurred in northwestern Texas and western Oklahoma, were many stations experienced average temperatures that ranged from 6 to 8 degrees F (3.33 to 4.44 degrees C) above normal. State average temperature Texas was 70.30 degrees F (21.28 degrees C), which makes it the third warmest April on record (1895-2012). For Oklahoma, it was their twelfth warmest April on record, with a state average temperature of 63.70 degrees F (17.61 degrees C). Arkansas reported its thirteenth warmest April on record (1895-2012) with a state average temperature of 64.10 degrees F (17.83 degrees C). Other state average temperatures include: Louisiana at 69.20 degrees F (20.67 degrees C), Mississippi at 65.40 degrees F (18.56 degrees C) and Tennessee at 60.30 degrees F (15.72 degrees C).
- With only a few exceptions, April was a very dry month for the Southern Region. In southern Louisiana, precipitation totals did dip over twice the monthly normal. Similar values were also observed along the Texas Gulf Coast, northern Texas, and in western and central Oklahoma. Elsewhere, most stations received less than half the expected precipitation for the month. The driest area of the region includes much of central Texas, where many stations reported only five percent of normal precipitation or less. Similar but less extreme dryness was also observed in north eastern Arkansas and throughout much of western and central Tennessee. Tennessee experienced its sixth driest April on record (1895-2012), with a state average precipitation total of only 2.17 inches (55.12 mm). Arkansas reported a state average precipitation total of 2.53 inches (64.26 mm), making it their eleventh driest April on record (1895-2012). For the state of Texas, it was their twenty-first driest April (1895-2012), with a state average precipitation total of 1.39 inches (35.31 mm). Other state precipitation totals include: Louisiana with 4.92 inches (124.97 mm), Mississippi with 3.63 inches (92.20 mm), and Oklahoma with 3.82 inches (97.03 mm).
- Drought conditions in the Southern Region improved for the third consecutive month. Although the total area of the region in drought has increased by approximately one percent, the amount of extreme drought has been decreased by approximately six percent. Much of this improvement occurred in western and southern Texas, which has been under the grip of drought for over a year. Some new drought has popped up in southern Tennessee, where it has been much drier than normal for two consecutive months.
- On April 3, 2012, several tornadoes touched down in the Dallas/Forth Worth Area. It is estimated that over 1,100 homes were damaged. In all there were 21 tornadoes that were confirmed, few injuries and fortunately no known fatalities. The storms were the result of a frontal system that pushed through the south central United States.
- On April 14, 2012, a tornado in Woodward, Oklahoma resulted in two fatalities. Major structural damage in western and northern Woodward.
- For more information, please go to the Southern Regional Climate Center Home Page.
- Western Region: (Information provided by the Western Regional Climate Center)
- The snow season typically declines significantly in the West as April ushers in a transition to warmer temperatures. A few precipitation events brought much needed moisture to California and added to the near-normal water year totals in the Pacific Northwest, while the Desert Southwest remained mostly dry.
- Periods of anomalously low and high temperatures averaged to near normal for the month as a whole for the coastal states, while more inland locations saw higher than average temperatures. The first week of the month gave a smattering of record lows west of the Rockies. April 5th and 6th saw back-to back record lows in Sacramento, CA at 35 F and 34 F (1.7 C and 1.1 C). On the 7th, Portland, Oregon hit a record daily low of 31 F (-0.6 C). Several other locations throughout California, Idaho, and Oregon also saw record daily lows during this period. A ridge built up the following week, bringing temperatures up to a daily record of 70 F (21.1 C) in Seattle, Washington on April 8, and setting three consecutive daily records at Idaho Falls, Idaho of 73 F, 76 F, 76 F (22.8 C, 24.4 C, and 24.4 C) on April 9-11. A stronger upper level ridge near the end of the month pushed the temperature at Reno, Nevada to 90 F (32.2 C) on April 22. This was the first 90 F (32.2 C) or greater day Reno has seen in April since airport records began in 1937, and earlier than the previous “first 90” by 8 days. Many daily records were set elsewhere in the Desert Southwest as well. At Death Valley, California temperatures soared to 110 F, 113 F, and 113 F (43.3 C, 45 C, and 45 C) on April 21, 22, and 23 setting a record at that location for most days over 110 F (43.3 C) in April. The previous record of two days occurred in both 1989 and 2007; records at Death Valley began in 1911. After a cold and snowy winter, temperatures in Alaska were mild and near normal for April. Several daily record highs were set at various locations throughout the state during the latter half of the month.
- April 10-14 brought copious amounts of precipitation to Central and Southern California. Several daily precipitation records with totals over 1 in (25.4 mm) were set throughout the region for this period. San Francisco airport received a total of 2.79 in (70.9 mm) of rainfall for the month, making this the 10th wettest April in the station’s 65-year record. The Pacific Northwest had a week of moderate precipitation between the 15th and 21st of April, followed by lighter rains at the end of the month. Over April 14th and 15th, Flagstaff, Arizona received 10 in (254 mm) of snowfall, setting a daily record and helping the location reach a precipitation total just over normal for the month.
- The Great Basin and Desert Southwest saw dry conditions and persistence or development of drought in April, with most locations well below normal precipitation values. Due to low snowpack and rapid melt of existing snowpack, spring and summer stream flow forecasts for these areas are at 50% of normal or less for these regions. Fire conditions in the Great Basin in April were already comparable to those normally experienced during the peak of summer. After a rainy March, Hawaii returned to dry conditions with Hilo, Big Island, only receiving 6.67 in (169.4 mm) for the month, 57% of normal. To the northwest, Lihue, Kauai received 0.37 in (9.4 mm) 19% of normal, though the location’s year-to-date total of 31.75 in (806.5 mm) remains well above average thanks to the high March totals.
- April 7: Anchorage, Alaska season snowfall record: On Saturday, April 7, Anchorage, Alaska received 4.3 in (109.2 mm) of snowfall, bringing the season total (since water year’s beginning on Oct 1, 2011) to 134.5 in (341.6 cm) and setting a record for greatest season snowfall at that location. This total narrowly eclipses the previous record of 132.6 in (336.8 cm) observed in 1954-55; snowfall records have been kept in Anchorage since 1915.
- April (all month): Fires in Western Great Basin: Due to the dry winter and warm April, the Western Great Basin has experienced over 60 fires so far this year, four times the usual number of fires for this region. Vegetative dryness this low is usually not seen for another 3-4 months.
- 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.
Note: The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed. Effective September 2012, the GHCN-M version 3.2.0 dataset of monthly mean temperature replaced the GHCN-M version 3.1.0 monthly mean temperature dataset. Beginning with the August 2012 Global monthly State of the Climate Report, released on September 17, 2012, GHCN-M version 3.2.0 is used for NCDC climate monitoring activities, including calculation of global land surface temperature anomalies and trends. For more information about this newest version, please see the GHCN-M version 3.2.0 Technical Report.
*The GHCN-M version 3.1.0 Technical Report was revised on September 5, 2012 to accurately reflect the changes incorporated in that version. Previously that report incorrectly included discussion of changes to the Pairwise Homogeneity Algorithm (PHA). Changes to the PHA are included in version 3.2.0 and described in the version 3.2.0 Technical Report. Please see the Frequently Asked Questions to learn more about this update.
Contents of this Section:
- The combined average temperature over global land and ocean surfaces for April 2012 was 14.35°C (57.87°F), which is 0.65°C (1.17°F) above the 20th century average of 13.7°C (56.7°F). The margin of error associated with this temperature is ±0.08°C (0.14°F). The global temperature departure from the 20th century average and the monthly rank were the highest since November 2010, near the onset of first back-to-back La Niñas in 2010.
- The combined average temperature over global land and ocean surfaces for April 2012 was 14.35°C (57.87°F), which is 0.65°C (1.17°F) above the 20th century average of 13.7°C (56.7°F). The margin of error associated with this temperature is ±0.08°C (0.14°F). The global temperature departure from the 20th century average and the monthly rank were the highest since November 2010, near the onset of first back-to-back La Niñas in 2010.
- The global land surface temperature was 1.39°C (2.50°F) above the 20th century average of 8.1°C (46.5°F), making this the second warmest April, behind 2007. The margin of error is ±0.11°C (0.20°F). Warmer-than-average conditions engulfed much of the world's land areas, with the most notable warmth across Alaska, the contiguous United States, Mexico, and most of Russia. Cooler-than-average conditions were present across northern Australia and parts of western Europe.
- The global land surface temperature was 1.39°C (2.50°F) above the 20th century average of 8.1°C (46.5°F), making this the second warmest April, behind 2007. The margin of error is ±0.11°C (0.20°F).
- For the ocean, the April global sea surface temperature was 0.38°C (0.68°F) above the 20th century average of 16.0°C (60.9°F)—the 11th warmest April on record. The margin of error is ±0.04°C (0.07°F).
- For the ocean, the April global sea surface temperature was 0.38°C (0.68°F) above the 20th century average of 16.0°C (60.9°F)—the 11th warmest April on record. The margin of error is ±0.04°C (0.07°F).
- The average Arctic sea ice extent during April 2012 was 1.8 percent below the 1979–2000 average, ranking as the 17th largest April extent since satellite records began in 1979 and the highest average April sea ice extent since 2001.
- On the opposite pole, Antarctic sea ice during April was 9.2 percent above average and ranked as the sixth largest April extent in the 34-year period of record.
- The Northern Hemisphere snow cover extent during April 2012 was much-below average, and ranked as the fourth smallest April snow cover extent in the 46-year period of record. Both the Eurasian and North American April snow cover extents were below average, ranking seventh and eighth smallest on record, respectively.
- Precipitation was variable across the globe during April. Above-average precipitation fell over areas that include most of Europe, southern Brazil, the central United States, and parts of eastern Asia. Below-average precipitation was observed across eastern Brazil, the eastern United States, and southern parts of South America and Australia.
The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed.
Temperature anomalies for April 2012 and January–April 2012 are shown on the dot maps in the following section. The dot maps on the left provide a spatial representation of anomalies calculated from the Global Historical Climatology Network (GHCN) version 3.1.0 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.
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 April 2012 map—is generally reflected by areas of positive and negative temperature anomalies at the surface, respectively.
Unlike March 2012, where extremely cool and warm temperatures engulfed much of the Northern Hemisphere land surfaces, most of the world's land areas experienced warmer-than-average temperatures during April 2012. The most notable warmth was observed across Russia, the United States, Alaska, and parts of the Middle East and western Europe. After experiencing very warm March temperatures, parts of western Europe experienced cooler-than-average temperatures, and in some locations the April 2012 temperatures were cooler than the March 2012 temperatures. Other areas that experienced cooler-than-average conditions during the month include southern South America, southeastern Africa, and northern Australia. Globally, the April 2012 land-only surface temperature was 1.39°C (2.50°F) above the 20th century average of 8.1°C (46.5°F)—the second warmest April in the 133-year record, behind 2007. This was also the warmest land-only monthly temperature departure from the 20th century average since November 2010 and the 137th consecutive month with global land temperatures above the 20th century average. The last time land-only worldwide temperatures were below average was November 2000 (0.02°C/0.04°F below average). Of note, the Northern Hemisphere land surface temperature was 1.74°C (3.13°F) above the 20th century average, marking the warmest April since records began in 1880.
Several national highlights are found below:
- The contiguous United States had a mean temperature of 13.2°C (55.7°F) in April 2012, which was 2.0°C (3.6°F) above the 20th century average, resulting in the third warmest April since national records began in 1895. Please visit NCDC's National State of the Climate report for additional information.
- The United Kingdom's (UK) mean temperature during April 2012 was 0.6°C (1.1°F) below the 1971–2000 average—the coolest April mean temperature since 1989. According to the UK's Met Office, April 2012 was cooler than March 2012, an unusual event that last happened in 1998. For the first time since April 1989, April daily temperatures never reached 20°C (68°F). Provisionally, England, Wales, and Scotland had their coolest April since 1989, while Northern Island experienced its coolest April since 2000.
- Spain experienced below-average temperatures during April 2012. According to Spain's National Agency of Meteorology (Agencia Estatal de Meteorología), the April 2012 national mean temperature was 12.1°C (53.8°F), which is 0.2°C (0.4°F) below the 1971–2000 average.
- According to Norway's Institute of Meteorology (Meteorologisk Institutt), Norway experienced cooler-than-average temperatures during April 2012. Temperatures during the month were 0.2°C (0.4°F) below average. This was the coolest April since 1998.
- Sweden also had its coolest April since 1998, according to the Swedish Meteorological and Hydrological Institute (SMHI).
- According to Germany's Weather Service (Deutscher Wetterdienst), Germany as a whole had a mean temperature of 8.1°C (46.9°F), which is 0.8°C (1.4°F) above the 1961–1990 average and the 47th warmest (or 86th coolest) April since national records began in 1881.
- In Antarctica, the South Pole station reported below-average temperatures during April 2012, with an average temperature of -59.6°C (-75.3°F), which is 2.1°C (3.8°F) below average. On April 6th, a new daily minimum temperature record was set when temperatures fell to -73.4°C (-100.1°F), surpassing the previous record of -71.7°C (-97.1°F) set in 1982. The period of record covers 1957–2012. The April 6th minimum temperature also broke the record for the earliest recording of -73.3°C (-100.0°F) at the South Pole station. The previous record of -75.2°C (-103.4°F) was set on April 7, 1982.
The worldwide ocean temperature during April 2012 was 0.38°C (0.68°F) above the 20th century average of 16.0°C (60.9°F)—the coolest April since 2008 and tied with 2011 as the eleventh warmest April on record. April 2012 was the 427th consecutive month with ocean temperatures warmer than the 20th century average. The last time the ocean temperatures were below average was September 1976 (0.01°C/0.02°F below average). A snapshot of the global temperatures indicates that warmer-than-average temperatures were observed across the North Atlantic, north-central Pacific Ocean, and across the mid-latitude southern oceans. Cooler-than-average conditions were present across the northeastern and central Pacific Ocean, parts of the southern half of the South Atlantic Ocean, and across the higher latitudes of the southern oceans. The El Niño-Southern Oscillation (ENSO), which is a climate pattern defined by a periodic fluctuation in sea surface temperature (El Niño) and the air pressure of the overlying atmosphere (Southern Oscillation) across the equatorial Pacific Ocean, transitioned from La Niña phase to neutral conditions during April 2012, as temperatures across the equatorial Pacific Ocean continued to warm. According to NOAA's Climate Prediction Center (CPC), ENSO-neutral conditions are expected to persist through the Northern Hemisphere summer 2012.
Averaging the global land and ocean as a whole, the combined land and ocean surface temperature during April 2012 was 0.65°C (1.17°F) above the 20th century average of 13.7°C (56.7°F), marking the fifth warmest April since records began in 1880 and the 326th consecutive month with a global temperature above the 20th century average. February 1985 was the last month with below-average temperatures, at 0.01°C (0.02°F) below average. This was also the warmest global land and ocean surface temperature anomaly since November 2010, near the onset of first back-to-back La Niñas in 2010.
(out of 133 years)
|Land||+1.39 ± 0.11||+2.50 ± 0.20||2nd Warmest||Warmest: 2007||+1.44||+2.59|
|132nd Coolest||Coolest: 1905||-0.79||-1.42|
|Ocean||+0.38 ± 0.04||+0.68 ± 0.07||11th Warmest||Warmest: 1998, 2010||+0.56||+1.01|
|123rd Coolest||Coolest: 1911||-0.53||-0.95|
|Land and Ocean||+0.65 ± 0.08||+1.17 ± 0.14||5th Warmest||Warmest: 2010||+0.75||+1.35|
|129th Coolest||Coolest: 1909||-0.52||-0.94|
|Land||+1.74 ± 0.14||+3.13 ± 0.25||1st Warmest||Warmest: 2000*||+1.62*||+2.92*|
|133rd Coolest||Coolest: 1905||-1.05||-1.89|
|Ocean||+0.37 ± 0.04||+0.67 ± 0.07||9th Warmest||Warmest: 2010||+0.59||+1.06|
|125th Coolest||Coolest: 1911||-0.52||-0.94|
|Land and Ocean||+0.89 ± 0.11||+1.60 ± 0.20||1st Warmest||Warmest: 2007+, 2010+||+0.87+||+1.57+|
|133rd Coolest||Coolest: 1909||-0.59||-1.06|
|Land||+0.47 ± 0.14||+0.85 ± 0.25||23rd Warmest||Warmest: 2005, 2007||+1.07||+1.93|
|111st Coolest||Coolest: 1917||-0.76||-1.37|
|Ocean||+0.41 ± 0.05||+0.74 ± 0.09||14th Warmest||Warmest: 1998||+0.61||+1.10|
|120th Coolest||Coolest: 1911||-0.52||-0.94|
|Land and Ocean||+0.42 ± 0.06||+0.76 ± 0.11||16th Warmest||Warmest: 1998||+0.66||+1.19|
|118th Coolest||Coolest: 1911||-0.52||-0.94|
|Ties: 1990, 1991|
* Please note that the value depicted as record year (2000) for the Northern Hemisphere land is the second warmest year on record.
+ Please note that the value depicted as record year (2007 and 2010) for the Northern Hemisphere land and ocean tie for the second warmest year on record.
The January–April map of temperature anomalies shows that warmer-than-average temperatures occurred across the contiguous United States, southern Canada, Mexico, southern South America, the United Kingdom, Scandinavia, northern Russia, and parts of southeastern Asia. Cooler-than-average conditions were observed across Alaska, northern Africa, central Asia, eastern Russia, and most of Australia.
The globally-averaged land and ocean temperature for January–April 2012 was 0.46°C (0.83°F) above the 20th century average of 12.6°C (54.8°F), the coolest such period since 2008 and the 15th warmest such period in the 133-year record. The land-only global average temperature anomaly of 0.75°C (1.35°F) above the 20th century average of 4.8°C (40.5°F) ties with 2011 as the 17th warmest such period and was the coolest such period since 1997. Meanwhile, the global ocean temperature tied with 1999 as the 13th warmest such period, with an anomaly of 0.35°C (0.63°F) above the 20th century average of 15.9°C (60.7°F)—the coolest January–April anomaly since 2008.
- The contiguous United States mean temperature during January–April was 7.4°C (45.4°F), which is 3.0°C (5.4°F) above the long-term average and the warmest such period since national records began in 1895. Please visit NCDC's National State of the Climate report for additional information.
- According to Norway's Institute of Meteorology (Meteorologisk Institutt), the January–April 2012 temperature for the country as a whole was 1.7°C (3.1°F) above the 1961–1990 average, resulting in the 20th warmest such period since national records began in 1900.
(out of 133 years)
|Land||+0.75 ± 0.22||+1.35 ± 0.40||Warmest||17th||2007||+1.38||+2.48|
|Ocean||+0.35 ± 0.04||+0.63 ± 0.07||Warmest||13th||1998, 2010||+0.56||+1.01|
|Land and Ocean||+0.46 ± 0.09||+0.83 ± 0.16||Warmest||15th||2010||+0.71||+1.28|
|Land||+0.87 ± 0.26||+1.57 ± 0.47||Warmest||18th||2007||+1.58||+2.84|
|Ocean||+0.32 ± 0.05||+0.58 ± 0.09||Warmest||13th||2010||+0.55||+0.99|
|Coolest||121st||1904, 1908, 1911||-0.46||-0.83|
|Land and Ocean||+0.53 ± 0.14||+0.95 ± 0.25||Warmest||16th||2007||+0.89||+1.60|
|Land||+0.43 ± 0.14||+0.77 ± 0.25||Warmest||22nd||2010||+1.02||+1.84|
|Ocean||+0.38 ± 0.04||+0.68 ± 0.07||Warmest||15th||1998||+0.60||+1.08|
|Land and Ocean||+0.39 ± 0.07||+0.70 ± 0.13||Warmest||17th||1998||+0.65||+1.17|
The most current data may be accessed via the Global Surface Temperature Anomalies page.
The maps below represent anomaly values based on the GHCN version 2 dataset of land surface stations using a base period of 1961–1990. During April 2012, above-average precipitation fell over areas that included the central and northwestern United States, and parts of northern and southern South America, Europe, and eastern Asia. Drier-than-average conditions were present across the eastern United States, the Hawaiian Islands, eastern Brazil, and southern parts of South America, and Australia.
- The decline of the La Niña brought to an end the wet conditions that eastern Australia had been experiencing for several months. According to Australia's Bureau of Meteorology, Australia experienced drier-than-average conditions across most of the nation, with 41 percent below-average rainfall. This was the 34th driest April in the nations 113-year record. Western Australia experienced 57 percent below-average precipitation in April, which was the lowest since April 2001.
- The United Kingdom received a total of 126.5 mm (5.0 inches) of precipitation during April 2012, which is the UK's wettest April since national records began in 1910. Provisionally, England had its wettest April on record, and also tied with 1998 with the highest number of rainy days in April in the last five decades.
- France experienced above-average precipitation, with 70 percent above average. This was France's wettest April since 1959 and fifth wettest since national records began.
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.
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 15 May 2012
Drought conditions across the US
as of 01 May 2012
Drought conditions gripped parts of the contiguous United States during April 2012. As of May 1st, 2012, 32 percent of the contiguous United States experienced moderate to exceptional drought, with 17 percent experiencing severe to exceptional drought, according to the U.S. Drought Monitor (USDM). Exceptional drought affected parts of western Texas, southeastern New Mexico, and across parts of Florida, Georgia, Alabama, and South Carolina. Conditions deteriorated across portions of the Carolinas and Georgia where less than 0.5 inch (12.7 mm) of precipitation fell. Please visit the US Drought page for additional information.
Copious rain fell across Western Province of Rwanda (located in central Africa) on April 12th, 2012, prompting flash floods. The floods inundated nearly 1,000 hectares of potatoes, maize, bananas, tea, and sugar, leading to food insecurity. Over 700 houses were either destroyed or damaged and nearly 11,000 people were affected.
Regions of Haiti submerged from
rains during 23–24 April 2012
Heavy downpours during the week of April 23rd in Haiti and the Dominican Republic prompted deadly floods and mudslides, affecting over 3,400 families in Haiti and more than 11,000 people in the Dominican Republic. Many of Haiti's improvised shelters are located in low-lying areas, resulting in some of them being flooded continuously, prompting concerns of sanitation risks to the population. According to reports, the copious rain claimed 16 lives across parts of southwestern and southern Haiti, with two people killed in landslides and the rest while trying to cross flood waters. Meanwhile, no fatalities or injuries were reported in the neighboring country of Dominican Republic. However, nearly 3,000 houses were damaged by the floods across northern and northeastern Dominican Republic. Torrential rain also fell across eastern Jamaica, flooding streets.
The Union of Comoros, which are islands located between northwestern Madagascar and eastern Africa, experienced torrential rains during mid-April. The heavy downpours caused severe floods and landslides, affecting over 46,000 people. According to reports, the floods damaged nearly 50 schools throughout the nation, and left three people dead and an estimated 100 people injuried.
Storm Reports for
03 April 2012
Source: NOAA's SPC
Severe thunderstorms spawned 17 devastating tornadoes across much of northern Texas on April 3rd, 2012, wreaking havoc across the affected area. The tornadoes destroyed homes, tossed tractor-trailer trucks, and left 17 people injured. One of the hardest hit areas was the densely populated area of Dallas, where two tornadoes (one rated an EF2 tornado and the other an EF0) ripped through the area, damaging 300 structures. According to the NWS, the EF2 tornado's maximum path width was 200 yards and had a length of 7.1 miles with estimated wind speeds of 130 mph (209 km/hr). The storms also produced two inch diameter or greater size hail, damaging more than 100 planes and canceling approximately 400 flights at Dallas/Fort Worth International Airport, leaving thousands of passengers stranded.
Bouts of severe weather continued to affect parts of the contiguous United States in April 2012. Severe storms on April 13th–15th produced nearly 150 preliminary tornadoes, large hail (3 inches in diameter), and strong winds, affecting portions of the central United States. An EF1 tornado touched down in Norman, Oklahoma near the University of Oklahoma campus, causing a few minor injuries and some property damage. Meanwhile, the town of Thurman, Iowa was hit by an EF2 tornado, leaving 75 percent of the town destroyed. An EF3 tornado caused over $280 million in damages across southeastern Wichita, Kansas, leaving 90 mobile homes damaged and, according to reports, destroying a building at a Spirit Aerosystems plant. The only deadly tornado was reported in Woodward Oklahoma, where six fatalities were reported. The tornado damaged or destroyed nearly 100 homes and buildings, and brought down trees and power lines. The governors of Kansas and Oklahoma declared states of emergency.
Please visit the U.S. Tornado report for additional information.
A severe storm brought strong winds and hail to northern provinces in Vietnam on April 20th. The strong winds blew roofs off homes and damaged over 4,500 homes and crops. Two people died when their house collapsed over them.
An unusuall late spring storm brought heavy snow to parts of the northeastern United States on April 23rd–24th, dumping nearly a foot of snow across some areas. The storm also brought strong winds to the affected areas, with LaGuardia Airport in New York observing a 54 mph (87 km/hr) wind gust—equivalent to a tropical storm. The vicious winds brought down power lines, leaving over 75,000 people without any power across Pennsylvania and upstate New York.
National Snow & Ice
Please Note: This will be the last monthly U.S. Snow and Ice Report until October 2012.
During April, warmer-than-average temperatures dominated much of the contiguous U.S., limiting snowfall during the month. Large areas of the nation, particularly the Northeast and the mountain West, were drier than average in April. At the beginning of the month, 8.2 percent of the Lower-48 was snow covered — the highest elevations in the West, and parts of the Great Lakes and Northeast. On April 30th, the percent area of snow coverage shrank to 4.1 percent with snow on the ground across the highest elevations in the West and parts of the Northeast. A late-season coastal storm dropped several inches of snow across the Northeast near the end of the month, causing some impacts across the region.
U.S. March Snow Cover Extent Anomalies
Source: Rutgers Global Snow Lab
According to data from the Rutgers Global Snow Lab, the monthly snow cover extent across the contiguous U.S. was approximately 114,300 square miles, which is 162,100 square miles below the 1981-2012 average. This was the third smallest April snow cover extent on record for the contiguous United States, slightly larger than the snow cover extents of April 1968 and 2004. Most regions of the country experienced below-average snow coverage, with the exception of the central Appalachians, where a late-season storm brought heavy snow accumulations. According to data from the U.S. Department of Agriculture, snowpack totals across the West were mixed at the end of April. The Pacific Northwest had snowpack levels which were much above normal, with near-normal snowpack stretching into the Northern Rockies. Parts of the Cascades and the Olympic Range in Washington had snow pack totals greater than 180 percent of normal. The rest of the mountainous West had much-below-normal snowpack totals, stretching from the Sierra Nevadas, across the Great Basin, and into the Central and Southern Rockies. Snow pack totals less than 25 percent of normal were widespread. The amount of snowpack at this time of year is important in determining the water supply for the region during the upcoming summer period.
Summary of Notable Snow Events:
24 April Northeast Snow Depth
Source: NOAA NNVL
A late-season storm dropped over a foot of snow from West Virginia to Upstate New York, along the higher elevations of central and northern Appalachian Mountains, on April 23rd and 24th. To the east, in the lower elevations, heavy rain fell across the large cities of the Northeast. This type of coastal storm, called a Nor’easter, was only the second of the season to impact the eastern seaboard, with the other being very early in the season in October. The snow storm was also on the heels of the warmest March on record for many locations across the region, where most trees already had begun to leaf. The snow falling on trees with leaves caused additional headaches by bringing down limbs and cutting power to at least 75,000 residents. The storm also resulted in at least 48 daily snowfall records. Although the storm did have some negative impacts, it provided drought-relieving precipitation for many locations in the Northeast.
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.
The weather pattern over North America in April 2012 was a continuation of the type of pattern which has dominated the circulation for the last several months. The main storm track hovered over the northern tier states and southern Canada for much of the month, but the jet stream had many wiggles in it, with associated cold upper-level troughs and warm upper-level ridges frequently migrating across the Lower 48 states. The contracted jet stream resulted in below-normal snow cover and warmer-than-normal temperatures across most of the country, while storm systems from the arching troughs and ridges brought a mixed pattern of precipitation. April 2012 had the third smallest April snow cover extent in the 1967-2012 satellite record for the contiguous U.S., and eighth smallest for North America. The month ended with an above-normal tornado count, mostly due to a strong storm system at mid-month.
The migrating troughs brought areas of precipitation to parts of the country throughout April (weeks 1, 2, 3, 4), which likely contributed to a below-normal wildfire count. On a monthly basis, the storm track generally brought above-normal precipitation to the western and north central states and below-normal precipitation to states from the Southern Plains to Great Lakes. Oregon had the seventh wettest April while Alabama and Tennessee ranked in the top ten driest category. Beneficial rains shrank the drought areas in parts of the West and the Northern Plains to Upper Midwest, but drought expanded in the Great Basin where Utah had the 38th driest April and Wyoming the 24th driest. Drought also expanded in the Northeast, where several states had the tenth driest, or drier, year-to-date (including Delaware and Maryland which both had the driest January-April in the 1895-2012 record), and in the Southeast (where Georgia ranked tenth driest for January-April 2012). By May 1, moderate to exceptional drought expanded to cover 69 percent of the Southeast and 38 percent of the contiguous United States, according to the U.S. Drought Monitor.
Since the warm upper-level ridges were migratory and did not stay in any given area a long time (weeks 1, 2, 3, 4), no state had the warmest April on record. However, four states in the Northeast and six from the Southern Plains to Mid-Rockies ranked in the top ten warmest category for April 2012. And during the days and in the locations where the ridges dominated, numerous daily record temperatures fell. Over 3800 daily high temperature records were broken or tied, including 332 of which were the highest maximum for the month of April. Over 2800 record warm daily low temperatures were tied or broken. In comparison, beneath the migrating upper-level troughs and associated cold fronts, only about 530 record low temperatures and about 660 record cool daily high temperatures were tied or broken. (These numbers are preliminary and are expected to increase as more data arrive.) The national Residential Energy Demand Temperature Index (REDTI) for April 2012 was the 23rd lowest April value in the 1895-2012 record, indicating heating fuel demand would be below the national average. 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 (February-April 2012), year-to-date (January-April 2012), and last six months (November 2011-April 2012).
When averaged together, the mixture of temperature and precipitation extremes gave the U.S. the third warmest and 41st driest April 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 preponderance of record warm highs (14th largest), record warm lows (7th largest), and large areas of dry conditions (14th largest) gave the U.S. only its 22nd largest CEI for April. 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 (February-April), year-to-date (January-April), and last 12 months (May-April), and the second highest CEI for the last six months (November-April). 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 February-April 2012, January-April 2012, November 2011-April 2012, and May 2011-April 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 April:
- Ocean temperatures and atmospheric circulation anomalies indicated that the equatorial Pacific had essentially transitioned from a La Niña state to an ENSO-neutral state during April. With the transition to a neutral state, ENSO normally would not be a player in April's weather; however, atmospheric circulation anomalies still showed some consistency with La Niña. The February-April 2012 temperature pattern does not match the La Niña temperature pattern for this time of year (nor do the February-April 2012 temperature and precipitation patterns match the El Niño temperature or precipitation patterns). Both the El Niño and La Niña drivers are correlated with large areas of negative temperature anomalies in different parts of the country.
- The Pacific/North American (PNA) pattern was positive at the beginning of the month but transitioned to negative by the end of the month. A positive PNA this time of year (April on the teleconnection maps) typically is associated with cooler-than-normal temperatures from the Southern Plains to Northeast and warmer-than-normal temperatures in the Northwest, while a negative PNA is associated with the opposite pattern (above normal in the Southern Plains to Northeast and below normal in the Northwest). The precipitation patterns are weakly correlated this time of year.
- The Arctic Oscillation (AO) pattern was neutral (zero) for most of the month with a slight negative dip near the end of the month. A negative AO this time of year (February-April) is typically associated with colder-than-normal temperatures across most of the country, dryness from the Mississippi Valley to Great Lakes and along the Pacific Northwest coast, and wet conditions in the Southeast. The February-April averaged upper-level circulation anomalies for a negative AO consist of an above-normal pattern over the Arctic, and below-normal pattern across the eastern two-thirds of the contiguous United States.
- The North Atlantic Oscillation (NAO) pattern started the month negative but transitioned to positive for most of the month. A positive NAO during this time of year (April on the teleconnection maps) is typically associated with drier-than-normal conditions in the Southeast, Central Plains, and mid-Pacific coast, while temperatures trend warmer than normal across most of the country.
The April 2012 averaged upper-level circulation anomalies are generally consistent with a positive NAO pattern across the Lower 48 States and northeastern Pacific Ocean. The pattern of observed temperature anomalies for April 2012 and the last three months (February-April) corresponds to the positive phase of the NAO across most of the country. The April 2012 and February-April precipitation patterns are a bit more complicated. As noted earlier, although the Pacific has essentially transitioned to an ENSO-neutral state, atmospheric circulation anomalies still showed some consistency with La Niña. This is evident by the dryness in the Southeast and Southwest and wetter-than-normal conditions in the Pacific Northwest. But dryness in the Southeast is also consistent with a positive NAO. It is difficult to associate the precipitation patterns in the rest of the country with any atmospheric circulation drivers when the drivers are neutral or in a state of transition.
Updated: 8 May 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:
- The NCDC Storm Events Database
- NOAA's Storm Prediction Center’s Data Page
- NOAA's Storm Prediction Center’s Preliminary Report Page
According to data from the Storm Prediction Center, the count of preliminary tornado reports during April — 228 — was above the 1991-2010 average of 155, but much less than the record breaking tornado month a year prior in April 2011. April tends to be one of the more active tornado months during the year, with annual tornado activity usually peaking in May.
On April 3rd, a series of supercell thunderstorms moved through the Dallas-Fort Worth Metroplex, spawning at least 17 tornadoes in the densely populated area. Most of the tornadoes were weak and rated EF0 and EF1, while three were rated EF2 and two were rated EF3. The Dallas-Fort Worth International Airport, one of the busiest in the nation, halted all flights and sheltered all passengers as a precaution due to the tornado warnings. The tornadoes caused significant damage across Dallas-Fort Worth, but they did miss the airport and there were no reported fatalities for the entire outbreak.
A large tornado outbreak impacted the Central Plains on April 14th, as a vigorous storm system swept through the region. There were 122 preliminary reports of tornadoes from Oklahoma to Iowa, with Kansas receiving the brunt of the action. Significant damage was reported as some of the tornadoes and severe thunderstorms were long-lived, producing long tracks of destruction. An EF-3 tornado, which moved through the town of Woodward, Oklahoma, struck during the overnight hours and led to six fatalities. This single outbreak accounted for most of the tornado reports during the month and the only reported tornado-related fatalities for April.
Contents Of This Report:
National Drought Overview
Detailed Drought Discussion
April 2012 was another warmer-than-average, but drier-than-average, month (3rd warmest on record and 41st driest, based on data back to 1895) when weather conditions are averaged across the country. Warm anomalies dominated at the monthly level, but migratory cold fronts brought regional cool anomalies at the weekly level (weeks 1, 2, 3, 4). The pattern for precipitation was variable, both on a monthly basis as well as a weekly basis (weeks 1, 2, 3, 4), although persistent dryness did occur over parts of the Midwest. Beneficial rainfall shrank drought in parts of the Upper Mississippi Valley, but continued dryness expanded the drought area in the Northeast, Southeast, and Hawaii. Nationally, the moderate-to-exceptional (D1-D4) drought footprint increased to about 32 percent of the country while the percentage in the abnormally dry category stayed roughly the same at about 50 percent.
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 Southern Plains (mostly western Texas) spreading into the Southwest (mostly New Mexico);
- moderate to extreme (D3) drought stretching from the Southwest to the West Coast and into the Pacific Northwest;
- moderate to exceptional drought in the Southeast, extending into the Mid-Atlantic states;
- expanding moderate to severe (D2) drought stretching from the Mid-Atlantic states into the Northeast, but limited to mainly along the coast;
- areas of moderate to severe drought in the Upper Midwest to Northern Plains; and
- parts 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.
As seen on the April 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 to Central Rockies, the Southern Plains and Southeast to Mid-Mississippi Valley, and Midwest to Northeast this month. Wet conditions are evident on the Z Index map across much of the Northwest and parts of the Central to Northern Plains. Compared with the March 2012 PHDI map, the April 2012 PHDI map indicates that drought conditions improved in the Northwest but intensified in the Southwest, Southeast, Upper Midwest, and Central Rockies, and expanded along the Northeast Coast and in parts of the Ohio Valley. The April 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 Northwest drought areas, and moisture conditions further declined across the Northeast and Ohio Valley; but for much of the Southeast, Southwest, Central Rockies, and Intermountain Basin — it was drier than normal over the existing drought 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.
Recent precipitation (March-April) has countered dryness earlier in the season (November-December), resulting in the Pacific Northwest having wet SPI values at 1, 2, 3, and 24 months, but essentially neutral at the 6 to 12 month time scales. The Four Corners states to Central Rockies are dry at 1 to 3 months, with the rest of the West (California and Nevada) generally wet at 1 to 2 months. The California-Nevada area transitions to dry at 3 to 12 months, while the Central Rockies dryness continues out to 12 months. In the western Great Lakes, a core of dryness is evident at 1 to 3 months, but is larger at 6 to 12 months, extending into the Northern Plains at 9 months. Dryness is evident from the Lower Great Lakes to Mid-Mississippi Valley at 1 to 3 months, but disappears at longer time scales. Dryness can be seen in the Southern Plains and adjoining Southwest at 1 month and 12-24 months, with wetness dominating in the Southern Plains at the intervening time scales. The Northeast is dry at 2-6 months but wet from 9 to 24 months, while the Southeast is generally dry at all time scales.
Agricultural and Hydrological Indices and Impacts
Drought conditions were reflected in numerous agricultural, hydrological, and other meteorological indicators, both observed and modeled:
- USGS (U.S. Geological Service) observed streamflow;
- NOAA Climate Prediction Center (CPC) modeled runoff anomalies and percentiles;
- VIC (University of Washington Variable Infiltration Capacity macroscale hydrologic model) 1-, 2-, 3-, and 6-month runoff percentiles;
- NLDAS (North American Land Data Assimilation System) modeled streamflow anomalies and percentiles;
- NLDAS model runoff anomalies and percentiles;
- USGS groundwater observations (real-time network, climate response network, total active network);
- USDA snow pack and snow water content observations for the West (SNOTEL station percentiles, SNOTEL station percent of normal, SNOTEL basin percent of normal and percent of average) and Alaska (SNOTEL station percent of normal, SNOTEL basin percent of normal);
- USDA reservoir storage as percent of capacity (with average depicted);
- USDA (U.S. Department of Agriculture) observed soil moisture conditions, departures and percentiles, and comparison to 5-year average and 10-year average;
- the Palmer Crop Moisture Index (CMI), which worsened and expanded during the month in the Southwest (weeks 1, 2, 3, 4);
- CPC modeled soil moisture anomalies and percentiles for end of April, soil moisture anomaly change compared to previous month;
- CPC's Leaky Bucket model soil moisture percentiles;
- NLDAS modeled soil moisture percentiles for the top soil layer and total soil layer;
- VIC modeled soil moisture percentiles, soil moisture percentile change compared to previous month;
- USDA observed pasture and rangeland conditions;
- Vegetation Drought Response Index (VegDRI);
- the NOAA/NESDIS satellite-based Vegetation Health Index (VHI);
- the USGS agro-hydrologic model (Soil Water Index, Water Requirement Satisfaction Index);
- total precipitation (plotted by the USGS, NOAA National Weather Service [NWS], and NOAA High Plains Regional Climate Center [HPRCC]);
- percent of normal precipitation and precipitation percentiles (NWS, HPRCC station observations, Leaky Bucket model);
- NCDC statewide precipitation ranks;
- USGS number of days with precipitation and maximum number of consecutive dry days;
- temperature departures from normal (HPRCC) and percentiles (Leaky Bucket);
- NCDC statewide temperature ranks;
- number of record warm daily low temperatures, record daily high temperatures, record daily low temperatures, and record cool daily high temperatures set in April 2012 (from NCDC's daily records analysis).
April 2012 was drier than normal for most of the stations in the Hawaiian Islands, resulting in an expansion of D1 (moderate drought) and D0 (abnormally dry conditions) as D2 contracted 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 where streamflow levels were below normal. As noted by the NWS, drought impacts continued in many areas.
The precipitation pattern over Alaska during April 2012 was predominantly drier than normal. Precipitation deficits are evident at longer time scales at some interior and southern stations (2, 3, 6, 12, 24, 36 months, year to date, and water year to date). However, snowpack and snow water content (for most stations and basins) were generally near to above normal (except for a few interior locations), and there was no drought or abnormal dryness indicated on the May 1st USDM.
The rainfall pattern across Puerto Rico during April was generally mixed. Drier-than-normal conditions become evident in a small southeastern area at longer time scales (2, 3, 6 months, year to date, and water year to date). With streamflow above average, the May 1st USDM map had no drought or abnormally dry areas on the island.
On a statewide basis, April 2012 ranked in the top ten driest Aprils for two states in the Southeast (Tennessee at sixth driest and Alabama at eighth driest), with Arkansas having the eleventh driest April in the 1895-2012 record. Eight other states from the Southern Plains to Great Lakes, and two in the West, ranked in the driest third of the historical record. Dryness in the Northeast stands out at the three month time scale, with 13 states from Tennessee to New England, plus Wyoming in the West, having the tenth driest, or drier, February-April. Connecticut ranked driest on record and New Jersey second driest. Four states in the West, and all but four east of the Mississippi River, ranked in the driest third of the historical record.
If the time period is extended another month back to include January, we still see dryness in the Northeast but drought in the West becomes more striking. January-April 2012 ranks in the top ten driest such four-month periods for seven states in the Northeast, one (Georgia) in the Southeast, and two (Colorado and Wyoming) in the West. Maryland and Delaware had the driest January-April, with New Jersey and Connecticut ranking second driest. Going back two more months (November 2011-April 2012) reveals pronounced dryness further west, with Nevada having the eighth driest such 6-month period, Utah tenth driest, and California twelfth driest. Three other states in the West, five in the Southeast, and ten in the Northeast 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. May 2011-April 2012 ranked in the top ten driest category for Texas, New Mexico, Florida, and South Carolina, with Georgia having the second driest such 12-month period.
The latest drought episode in the contiguous U.S., which gained steam in early 2011, has waned on a national scale in recent months. But while the percent area of the country in extreme to exceptional drought has dropped from a peak of about 19 percent during the summer of 2011 to about 7 percent at the end of April 2012, the percent area in moderate to exceptional drought continued to climb during this period, hovering near 40 percent at the end of April. This trend is reflected in the national Palmer Z Index, which integrates drier-than-normal (water supply) and warmer-than-normal (water demand) conditions across the nation on a month-by-month basis. The national monthly Palmer Z Index for January 1998-April 2012 indicates that, from June 2011 through April 2012, dry and warm conditions have combined to cause overall drought conditions to persist when integrated across the country. On a regional basis, the South has shown a dramatic improvement in all categories in recent months, while drought continued to linger in the Southeast. Similar trends can be seen on a statewide basis in Texas, New Mexico, and Georgia.
Pacific weather systems moving across the West brought above-normal precipitation to the coastal states during April 2012. But drier-than-normal conditions dominated from the Southwest and intermountain basin to the Central Rockies. Dry weather has been the rule 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 West. Mountain snow pack and snow water equivalent (basin averages as well as station percent of normal and percentiles) were near to above normal in parts of the Northwest, but to the south conditions were much drier with many stations having near-record low snow water content. Low precipitation as well as above-normal temperatures, which accelerated melting, contributed to the low snowpack. Mountain snowpack is a crucial water supply during the following melt season. Fortunately, the reservoirs in most states were near to above normal, with just Arizona and New Mexico averaging below normal statewide. According to the USDM, 46 percent of the West was experiencing moderate to exceptional drought at the end of April, a 3 percent decrease compared to March. The Palmer Drought Index statistic was about 44 percent, reflecting a remarkable rise over the last four months.
A more detailed drought discussion, provided by the NOAA Regional Climate Centers and others, can be found below.
West — Upper Colorado River Basin — Pacific Islands
As noted by the Southeast Regional Climate Center, monthly precipitation was below average across most of the Southeast in April, while mean temperatures were generally above average. In particular, the southern tier of the region (except for South Florida), as well as eastern portions of North Carolina and northern Virginia, recorded less than 50 percent of normal precipitation for the month. The driest locations were found across central portions of Alabama and Georgia, where monthly precipitation totals were less than 25 percent of normal. Columbus, GA recorded 0.49 inch (12.5 mm) of precipitation for the month, making it the second driest April in a record extending back to 1948. Monthly precipitation was 50 to 100 percent of normal across the interior of Puerto Rico, but as much as 200 percent of normal along the southern and eastern slopes.
Drought conditions continued to worsen across the Southeast in April. One notable exception was South Florida, which saw an elimination of drought conditions due to the heavy rains there. The area of exceptional drought (D4) expanded across southeast Alabama, southern Georgia, and into the northeast Panhandle of Florida, while the area of extreme drought (D3) expanded into South Carolina and central Florida. Areas of severe drought (D2) expanded into southeast Virginia, while moderate drought (D1) conditions re-emerged across northern sections of Alabama and Georgia. The warm, dry weather contributed to several large wildfires, including one that burned over 35,000 acres near the Florida-Georgia border and impacted air quality from the northeast Florida Panhandle all the way to the Tampa Bay area. Warm temperatures and lack of precipitation over the past six months continued to reduce stream flow and groundwater levels across parts of the Southeast, particularly southern Georgia where most gauge stations were in the bottom 10 percent or at their record low level by the end of April. Conversely, the warm weather resulted in Florida watermelons shipping as much as 2 weeks early with larger volumes than last year. The cold weather at the beginning and end of the month caused damage to the apple, blueberry, and blackberry crops in western North Carolina, with projected losses exceeding 40 percent. The cold weather also caused damage to the Bermuda grass that had begun to emerge across northern Georgia.
As explained by the Southern Regional Climate Center, with only a few exceptions, April was a very dry month for the Southern region. Most stations received less than half the expected precipitation for the month. The driest area of the region included much of central Texas, where many stations reported only five percent of normal precipitation or less. Similar but less extreme dryness was also observed in northeastern Arkansas and throughout much of western and central Tennessee. Tennessee experienced its sixth driest April on record (1895-2012), with a state average precipitation total of only 2.17 inches (55.12 mm). Arkansas reported a state average precipitation total of 2.53 inches (64.26 mm), making it their eleventh driest April on record (1895-2012). For the state of Texas, it was their 21st driest April (1895-2012), with a state average precipitation total of 1.39 inches (35.31 mm). Like March, April was generally a warmer-than-normal month for the region.
Drought conditions in the Southern region improved for the third consecutive month. Although the total area of the region in drought increased by approximately one percent, the amount of extreme drought decreased by approximately six percent. Much of this improvement occurred in western and southern Texas, which has been under the grip of drought for over a year. Some new drought popped up in southern Tennessee, where it has been much drier than normal for two consecutive months.
As summarized by the Midwest Regional Climate Center, April temperatures were near normal in the eastern part of the Midwest and above normal in the western parts of the region. April precipitation varied with above-normal precipitation in most of the western half of the Midwest and below-normal precipitation in the southeastern half of the region. Totals exceeded 150 percent of normal in parts of Minnesota, Missouri, and Illinois while totals failed to reach 50 percent of normal further to the south and east, including parts of Missouri, Illinois, Kentucky, Indiana, Ohio, and Michigan. April snows were recorded in the northern parts of Minnesota, Wisconsin, Michigan, and Ohio with only north central Minnesota topping normal for the month. Though the total Midwest area in drought shrank slightly in April, the locations affected spread into parts of Illinois and Kentucky.
As noted by the Northeast Regional Climate Center, precipitation totals averaged below normal for the third consecutive month. April's regional total of 2.95 inches (74.9 cm) was 81 percent of normal. Maine was the sole state to average wetter than normal and had a departure of 121 percent. Departures among the drier-than-normal states ranged from 91 percent in Vermont to 55 percent in Pennsylvania, where it was the 16th driest April in 118 years. It was the driest January through April since 1895 in Delaware and Maryland, the second driest in Connecticut and New Jersey, and the fifth driest in New Hampshire and the Northeast. The Northeast's average temperature was 46.8 degrees F (8.2 degrees C) in April. This was only 0.6 degrees F (0.3 degrees C) warmer than normal — the average this month was the closest to normal since August 2011 when the departure was +0.5 degrees F (0.3 degrees C). It was the first month since October 2011 that all the states in the region did not average warmer than normal.
Four consecutive dry and warm months worsened the drought conditions in parts of the Northeast. As of April 24, 2012, the USDM had much of the eastern third of the region in moderate (D1) to severe (D2) drought. A few locations in Massachusetts had implemented mandatory or voluntary outdoor water use restrictions during the month. The agricultural community in Delaware and eastern Maryland was also impacted by the dry weather — some farmers have waited to plant crops due to low soil moisture while others have been irrigating — a practice not typically needed during the spring. An increase in brush fires throughout the region prompted bans on outdoor burning. One fire in southeastern New York destroyed 30 buildings and spread over 50 acres at a former Catskill resort. A late season Nor'easter brought up to 3 inches (76.2 mm) of much needed rain to eastern New England on the 23rd, easing drought concerns there.
As explained by the High Plains Regional Climate Center, the region was warm again this month — similar to March, based on preliminary data, every station in the region had above-normal temperatures. Precipitation varied across the region. Much of the eastern half of the region had precipitation totals which were higher than normal, while lower than normal precipitation areas included most of Wyoming, the western half of Colorado, central and northeastern Kansas, and isolated pockets in Nebraska and the Dakotas. Snowfall was sparse this month and due to the continued warmth, snow pack has declined in the mountainous portions of the region. According to the Natural Resources Conservation Service, by the end of the month, the statewide snowpack was 19 percent of average in Colorado and 45 percent of average in Wyoming. The low snowpack has raised concerns about irrigation water availability for the growing season. In addition, according to the Denver Post, Independence Pass was scheduled to open two weeks ahead of schedule because of the lack of snow in the mountains. The pass usually opens the Thursday before Memorial Day weekend.
There were many changes again to the USDM this month. The drought conditions in the areas near the Colorado-Kansas border continued to improve as all extreme drought conditions (D3) were erased and only a couple of small areas of severe drought conditions (D2) remained. In eastern South Dakota, D2 was downgraded to moderate drought conditions (D1) and some drought conditions were completely eliminated in the northwest portion of the state. Although recent rains have led to improvements in these areas, others have seen degradation. The small area of D2 in western Colorado expanded to include much of the west-central portion of the state. A patch of D1 that was in western South Dakota was extended north into North Dakota and south into the panhandle of Nebraska. Abnormally dry conditions (D0) also expanded to include eastern Wyoming and small areas of D1 crept into southern portions of the state.
As summarized by the Western Regional Climate Center, the snow season typically declines significantly in the West as April ushers in a transition to warmer temperatures. A few precipitation events brought much needed moisture to California and added to the near-normal water year totals in the Pacific Northwest, while the Desert Southwest remained mostly dry. Periods of anomalously low and high temperatures averaged to near normal for the month as a whole for the coastal states, while more inland locations saw higher than average temperatures. After a cold and snowy winter, temperatures in Alaska were mild and near normal for April. Several daily record highs were set at various locations throughout the state during the latter half of the month.
The Great Basin and Desert Southwest saw dry conditions and persistence or development of drought in April, with most locations well below normal precipitation values. Due to low snowpack and rapid melt of existing snowpack, spring and summer stream flow forecasts for these areas were at 50 percent of normal or less for these regions. Fire conditions in the Great Basin in April were already comparable to those normally experienced during the peak of summer. Due to the dry winter and warm April, the Western Great Basin has experienced over 60 fires so far this year, four times the usual number of fires for this region. Vegetative dryness this low is usually not seen for another 3 to 4 months. After a rainy March, Hawaii returned to dry conditions with Hilo, Big Island, only receiving 6.67 in (169.4 mm) for the month, 57 percent of normal. To the northwest, Lihue, Kauai received 0.37 in (9.4 mm) 19 percent of normal, though the location's year-to-date total of 31.75 in (806.5 mm) remained well above average thanks to high March totals.
Upper Colorado River Basin: As reported by the Colorado Climate Center, the May 1st NIDIS (National Integrated Drought Information System) assessment for the Upper Colorado River Basin (UCRB) indicated that, 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 (seasonal peaks one month earlier than normal). Nearly all of the sub-basins were near or below 30 percent of average. The lowest averages were in eastern Utah. 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 fifth percentile or below. The Wasatch range in Utah and the northern mountains of Colorado were also dry, with most precipitation percentiles in the teens. The VIC model showed dry soil moisture conditions in eastern Colorado, in Utah around the Colorado River and Green River valleys, and in southern Wyoming. The VIC showed very wet soils around the Colorado headwaters region (likely due to early melting of snowpack infiltrating the soils). When VIC snow water equivalent (SWE) and soil moisture are combined, the UCRB showed a moisture storage deficit. All of the reservoirs above Lake Powell were above their April storage averages. Lake Dillon and Flaming Gorge saw storage volume decreases since the beginning of the month. The rest of the major reservoirs increased in volume since the beginning of the month. Lake Powell was at 84 percent of average and 64 percent of capacity (compared to 52 percent one year ago). Compared to 2002 (the UCRB's most severe drought in recent history), water supply was in better condition with all of the major reservoirs above Lake Powell at higher levels than in April of 2002.
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, below-normal rainfall in April kept drought firmly in place over leeward areas of Maui County and the Big Island. In Maui County, extreme drought conditions, or the D3 category in the USDM map, continued over western Molokai and southwest Maui from Kihei to Makena. Severe drought, or D2 category conditions, covered the island of Lanai, the lower leeward slopes of the west Maui mountains and leeward Haleakala from Kula to Kaupo. On the Big Island, extreme drought continued to cover portions of the south Kohala district and the Pohakuloa region of the Hamakua district. Severe drought maintained its presence over the lower elevations of the north and south Kona districts and the western portion of the Kau district. Kauai, Oahu and windward sections of the Big Island and Maui were drought-free. The end of April marked the fourth consecutive year with drought persistence through the wet season within the state of Hawaii.
Some drought impacts in Hawaii include the following:
- On Kauai, there were no drought impacts to report.
- On Oahu, the water supply in the Waimanalo reservoir has increased to pre-drought levels. On April 23, the state Department of Agriculture rescinded the mandatory 10 percent water use restriction for the Waimanalo reservoir. A voluntary 10 percent reduction in water use has taken its place as a precaution heading into 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, pastures and general vegetation conditions have been very poor. An earlier report indicated that axis deer have been encroaching populated areas of the island for forage due to poor supplies elsewhere.
- On Maui, late February and early March rainfall helped bring some improvements to pastures and vegetation. However, a lack of follow-up rain during the remainder of March and most of April resulted in a resumption of deterioration over the leeward sections of Maui. Some ranchers have destocked pastures in these areas due to poor forage conditions. One 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 were in very poor condition. 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.
On other Pacific Islands (maps — Micronesia, Marshall Islands, basinwide), April was drier than normal for Chuuk, Kosrae, Kwajalein, Pohnpei, and Saipan, but near to above normal for the rest of the stations. The last two months have been drier than normal for Kosrae, Kwajalein, and Saipan. According to the May issue of the Pacific ENSO Update, vegetation on the islands of the Commonwealth of the Northern Mariana Islands (CNMI) has become wilted and brown, several wildfires were observed on Guam, and recent dry spells have affected some of the northern islands of Chuuk State, Pohnpei Island and the eastern islands of Pohnpei State, Kosrae, and some of the northern atolls of the Republic of the Marshall Islands (RMI). Total rainfall for the last 12 months (May 2011-April 2012) was near to above normal for all stations except Pago Pago.
|Station Name**||May 2011||Jun 2011||Jul 2011||Aug 2011||Sep 2011||Oct 2011||Nov 2011||Dec 2011||Jan 2012||Feb 2011||Mar 2012||Apr 2012||May 2011-Apr 2012|
** Clicking on the station name will reveal a climatology graph of the normal monthly rainfall.
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.):
|northeast u. s.||east north central u. s.||central u. s.|
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- Palmer Drought Indices
- Standardized Precipitation Index
- long-term (36 to 60 month) percent of normal precipitation maps
- airport station percent of normal precipitation maps
- statewide precipitation rank maps
- Cooperative station percent of normal precipitation maps
- percent of average maps for the SNOTEL stations in the western mountains provided by the Western Regional Climate Center
- satellite-based observations of vegetative health
- National Weather Service model calculations of soil moisture, runoff, and evaporation
- National Weather Service model calculations of soil moisture using the Leaky Bucket Model
- Midwest Regional Climate Center model calculations of soil moisture
- topsoil moisture conditions observed by the USDA and mapped by the Climate Prediction Center
- pasture and range land conditions observed by the USDA and mapped by the Climate Prediction Center
- streamflow maps maintained by the USGS
Contacts & Questions
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 during April 2012 was much below average and ranked as the fourth smallest April snow cover extent in the 46-year period of record. The monthly snow cover extent was 2.2 million square km (850,000 square miles) below the long-term average of 30.4 million square km (11.7 million square miles). Both the North American and the Eurasian land areas had snow cover extents below average for the month.
During April 2012, the North American snow cover extent was below average, ranking as the eighth smallest April snow cover extent on record. Warmer-than-average temperatures were present across much of the United States and southern Canada during the month, which limited snow cover across those locations. Above-average snow cover was observed in western Canada. The monthly snow cover extent was 12.2 million square km (4.7 million square miles), which is 932,000 square km (360,000 square miles) below average.
Eurasian snow cover extent during April was 15.9 million square km (6.1 million square miles), which was 1.2 million square km (463,000 square miles) below average, ranking as the seventh smallest April snow cover extent on record. During the month, below-average snow cover was observed across central and eastern Russia, northern China, and much of Kazakhstan. Above-average snow cover was present for western Russia and the Tibetan Plateau.
Sea Ice Extent
According to the National Snow and Ice Data Center (NSIDC), the Northern Hemisphere sea ice extent — which is measured from passive microwave instruments onboard NOAA satellites — averaged for April 2012 was 14.73 million square kilometers (5.69 million square miles), 1.8 percent below the 1979-2000 long-term average, and the 17th smallest (18th largest) April sea ice extent in the 1979-2012 period of record. This was the largest April Arctic sea ice extent since 2001. The relatively large April ice extent, in comparison to recent years, was due to a slow rate of ice loss during the first full month of the melt season. April 2012 is the 13th consecutive April and the 131st consecutive month with below-average Arctic ice extent. April Arctic sea ice extent has decreased at an average rate of 2.4 percent per decade.
According to the analysis by the NSIDC, during April, Arctic sea ice was much above average in the Bering Sea, as it was for most of the winter season. Ice extent was below average across Baffin Bay and the Sea of Okhotsk. The areas with above-average ice extent coincided with locations that experienced below-average temperatures in April, and areas with below-average ice extent were consistent with locations experiencing above-average temperatures.
The April 2012 Southern Hemisphere sea ice extent was 7.97 million square km (3.1 million square miles), 9.2 percent above the long-term average — the sixth largest April extent in the 1979-2012 period of record. This marks the largest Antarctic sea ice extent since 2009. Throughout the month, Southern Hemisphere sea ice trended above average. Southern Hemisphere sea ice extent has increased at an average rate of 2.4 percent per decade, with substantial inter-annual variability.
For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page.
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*RATPAC rank is based on 55 years of data
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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.
- Christy, John R., R.W. Spencer, and W.D. Braswell, 2000: MSU tropospheric Temperatures: Dataset Construction and Radiosonde Comparisons. J. of Atmos. and Oceanic Technology, 17, 1153-1170.
- Free, M., D.J. Seidel, J.K. Angell, J. Lanzante, I. Durre and T.C. Peterson (2005) Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC): A new dataset of large-area anomaly time series, J. Geophys. Res., 10.1029/2005JD006169.
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Updated: 8 May 2012
During April, wildfire activity across the U.S. was below average, although warm and dry conditions occurred across a large portion of the country. The 191,062 acres which burned in April was the fifth least in the period of record, and the 7,506 fires was also the fifth least.
(out of 13 years)
|Acres Burned||191,062||9ᵗʰ Most||1,791,469||2011||291,738|
|Number of Fires||7,506||9ᵗʰ Most||13,747||2006||8,645|
|Acres Burned per Fire||25.5||8ᵗʰ Most||290.6||2011||48.6|
(out of 13 years)
|Acres Burned||373,479||9ᵗʰ Most||2,380,885||2011||719,143|
|Number of Fires||17,857||11ᵗʰ Most||34,689||2006||22,897|
|Acres Burned per Fire||20.9||8ᵗʰ Most||102.5||2011||29.6|
*Data Source: The National Interagency Fire Center (NIFC)
As a whole, the contiguous U.S. had its third warmest April on record, with warmer-than-average temperatures across the central regions of the country, as well as the Northeast. Precipitation totals were mixed during April, with wetter-than-average conditions across the West Coast, the Northern Rockies, and the Northern and Central Plains. Dry conditions were present across the Southeast, stretching northward into the Great Lakes. 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 Drought (D1-D4) grew from 36.8 percent at the beginning of April to 38.2 percent at the beginning of May. Drought conditions continued to deteriorate along the Eastern Seaboard, particularly in the Northeast and Southeast. Drought remained generally unchanged across the Southern Plains. The drought picture was mixed across the West. Above-average precipitation across parts of California improved drought conditions by one category there, while dry conditions across the interior West led to worsening drought.
The County Line fire, which burned in northern Florida during most of the month, was fully contained by the end of April. The fire was ignited on April 5th by a lightning strike, and very dry conditions across the region provided ample fuel for the flames. By the end of the month the fire had charred nearly 35,000 acres. The main impact from the fire was the smoke plume which led to poor air quality conditions in Jacksonville, Florida, the state’s most populous city.
Dry, windy, and warm conditions across the Northeast caused ideal wildfire conditions during the middle of April. Wildfires were reported across New England, New Jersey, and Long Island. The largest impact from the flames was the low air quality conditions across the densely populated region.
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 April, there were 13 large wildfires burning across the country. Three large fires were burning across the Southern Appalachians of Virginia and Tennessee, where moderately low 10-hour fuel moistures were observed. Four large wildfires were active across South Dakota and Nebraska, where low 1,000-hour fuel moistures were observed. Three fires were burning in Kansas and Missouri which were experiencing low 10-hour fuel moistures at the end of the month. One fire was burning in the panhandle of Florida, where high KBDI values were present. The last fire burning was the Lower North Fork Fire in Colorado, where low 10-hour and 100-hour fuel moistures combined with very strong winds to create high fire danger.
On April 15th, there were five large wildfires burning nationwide. Three of the fires were burning in the central Appalachians of Virginia and Kentucky, where moderate fire danger and low 10-hour fuel moistures were observed. One large wildfire was active in New Mexico, where ongoing drought conditions led to increased fire danger, high KBDI values, and low fuel moistures. The County Line Fire in Florida was also burning, where very high KBDI values were observed.
At the end of April, there were six large wildfires active. The County Line Fire continued to burn in Florida. Two large wildfires were burning in west Texas, where ongoing drought conditions contributed to very high fire danger, high KBDI values and low 10-hour and 100-hour fuel moistures. Two fires were active in Nevada, where shorter term drought led to high KBDI values and fire danger, and extremely low 10-hour fuel moistures. One additional fire was active in Minnesota, where high fire danger was observed.