Drought - February 2011
NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.
Contents Of This Report:
National Drought Overview
Detailed Drought Discussion
February 2011 ranked near the middle of the 117-year historical distribution (41st driest and 51st coolest, based on data back to 1895) when weather conditions are averaged across the country. But this reflected regional extremes (monthly precipitation and temperature) which resulted from the changing weekly regional patterns of precipitation (weeks 1, 2, 3, 4) and temperature (weeks 1, 2, 3, 4) anomalies throughout the month. Beneficial precipitation fell across parts of the drought areas in the Southeast early in the month and Ohio Valley/Midwest later in the month. But precipitation totals for the entire month were drier than normal over most of the drought and abnormally dry areas as well as parts of the north central states and Far West. The drought area contracted in the Ohio Valley, but abnormally dry to extreme drought conditions expanded across parts of the Southern Plains to Southeast, and moderate to severe drought expanded across parts of the Southwest. Severe drought slightly contracted but moderate drought expanded in Hawaii, especially on the Big Island. About 28 percent of the contiguous U.S. was experiencing moderate to extreme drought at the end of February, reflecting a steady rise in drought extent since last summer when the percent area dropped to the lowest value in the USDM 11-year record.
February 2011 had a very active weather pattern over the contiguous United States. A high amplitude circulation (one with many troughs and ridges and low pressure sytems) dominated during the first part of the month, resulting in winter storm sytems moving across many parts of the country. Significant troughing occurred in the West early in the month, sending very cold Canadian air plunging into the Lower 48 States. The cold air followed a strong low pressure system which increased national snow cover to its greatest February 2011 extent of about 65 percent of the country by the 10th. February 2011 snow cover was the 9th largest February extent for the contiguous U.S. and 8th largest for North America in the 45-year satellite snow cover extent record.
The circulation pattern switched to a more zonal flow later in the month, with the storm track more along the northern states. Temperatures moderated when the circulation pattern flattened at mid-month, but the month ended with surges of cold air behind strong cold fronts which brought tornado outbreaks on the 24th and 27th-28th. There were 59 preliminary tornado reports during February 2011, ranking the month in the top ten busiest Februaries. The Southeast drought areas received beneficial preciptation early in the month, but the shift of the storm track further north later in the month left the South dry while bringing relief to the Midwest and Ohio Valley drought areas. February ended with moderate to extreme drought covering 23 percent of the U.S., about 3 percent higher than at the end of January. Wildfire activity was high during the month, particularly across the South and Southeast drought areas, with a record high February number of wildfires and second highest for acres burned. The mid-month circulation shift was accompanied by a surge of winter storms into the West, whose rain and snow ended a one and a half month lull in precipitation. The month started with about half (52.2 percent) of the country covered in snow and ended with about half (49.5 percent) snowcovered.
The circulation pattern flip-flop resulted in nationally-averaged temperature and precipitation ranks in the middle of the 117-year historical distribution (51st coolest and 41st driest February). But extremes occurred on the state level, with Wyoming having the 15th coolest February, Virginia the 21st warmest, Louisiana and Mississippi 8th driest, and Ohio (5th wettest), South Dakota (6th wettest), and Indiana (10th wettest) each in the top ten wettest category.
Cold fronts and low pressure systems moving in the storm track flow are influenced by the broadscale atmospheric circulation. Two such large-scale atmospheric circulation patterns were dominant during February. The first was a weakening La Niña, which is the phenomenon created by cooler-than-average sea surface temperatures in the eastern tropical Pacific Ocean. At this time of year, La Niña is typically associated with dry conditions in the Southwest, Southeast, and southern Plains, a wet signal along the Ohio Valley and in the northern tier states, and warmer-than-normal temperatures across most of the country, especially in the Southwest. The second atmospheric circulation index was the Pacific/North American (PNA) pattern, which transitioned from a weak positive or neutral phase during the first part of February to a negative PNA during the last half of the month. A negative PNA this time of year is typically associated with warmer-than-normal temperatures over the southeast third of the U.S., colder-than-normal temperatures in the Northwest, and wetter-than-normal conditions in the Pacific Nothwest and from the Ohio Valley northward. The pattern of observed temperature anomalies for February 2011 generally matched the La Niña and negative PNA in the East. In the West, the negative PNA pattern dominated, except the cold anomalies encompassed a larger area than normally associated with a negative PNA. This is associated with strong troughing in the West and ridging in the Southeast in the monthly averaged circulation. The observed precipitation pattern in February east of the Rockies largely matched the pattern expected from La Niña and a negative PNA, especially in the Southwest.
By the end of the month, the core drought areas in the U.S. included:
- a band of moderate (D1) to extreme (D3) drought which stretched from the Southwest, across the Southern Plains, to the Southeast and Mid-Atlantic States;
- parts of Hawaii, where moderate to extreme drought persisted; and
- the Central High Plains, where moderate to severe (D2) drought continued.
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 Palmer Z Index map, low precipitation resulted in dry conditions for February 2011 in a band from the Mid-Atlantic States to Texas, the southern half of Florida, parts of the western Great Lakes, and parts of the Northwest and Southwest. Wet conditions for February are evident on the Z Index map from much of the Northeast to Midwest, and across parts of the northern Plains and West. Near-normal conditions occurred in a band across the coastal Southeast. Compared with the January 2011 PHDI map, the February 2011 PHDI map indicates that drought conditions intensified in parts of the Gulf Coast States; drought conditions contracted in the Ohio Valley; and moist conditions persisted across much of the Upper Midwest, Northern Plains, and parts of the West. The February 2011 PHDI map also reflects the long-term nature of the drought conditions. The Z Index and PHDI maps in combination show that the dryness in the Southeast to Southwest is both a short-term and long-term phenomenon; that the dryness in the western Great Lakes is a short-term phenomenon; that the wetness in the Ohio Valley is also a short-term phenomenon; and that the wetness in the northern Plains and parts of the Rockies is both a short-term and long-term phenomenon.
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. Dryness is evident across parts of the Southwest, Deep South, and Mid-Atlantic States from 1 month to 9 months to 12 months, and across much of this area and the Southern Plains at 3 to 6 months. Dryness in parts of the Great Lakes occurs at 1 month to about 6 months. Parts of the Northwest were dry at the 1-month time scale, and much of the West was dry at 2 months, but large areas of wetness show up across the West at the 3- to 12-month time scales. Much of the Northeast to central Midwest was wet at the 1-month time scale, with parts of this area wet at 2 months. The Northeast is wet from 6 to 24 months. The Northern Rockies and Northern Plains are persistently wet at most time scales, especially the 3- to 24-month time scales. Dryness is rare at 24 months.
Abnormal dryness and drought were evident in several indicators. There were hardly any days with precipitation across the Southern Plains, Southwest, Great Basin, and parts of interior Northwest, as well as southern Florida and the northwestern Great Lakes. This resulted in long runs of consecutive dry days in these areas. Long dry runs (2 weeks or longer) also occurred across much of the Southeast. The dryness is also reflected in low total precipitation amounts and below-normal precipitation. On the other hand, it rained or snowed half or more of the days of the month along the coastal Pacific Northwest and parts of the Northern Rockies and eastern Great Lakes. During the winter cold season, vegetation goes dormant across much of the country. But soil moisture, as monitored by several models (NOAA Climate Prediction Center [CPC] anomalies and percentiles, Leaky Bucket, NLDAS [North American Land Data Assimilation System] top soil layer and total soil layer, VIC [University of Washington Variable Infiltration Capacity macroscale hydrologic model] percentiles), continued very dry from the Mid-Atlantic States to the Lower Mississippi Valley, with areas of dryness across the Southwest to Southern and Central High Plains, lingering dryness in parts of the Ohio Valley and southern Great Lakes, and a hint of dryness in parts of Alaska and Hawaii. Satellite monitoring of vegetation health (Vegetation Drought Response Index [VegDRI], Vegetation Health Index [VHI]) indicated stress on vegetation in parts of the Southwest, Southern to Central Plains, Southeast, and Ohio Valley.
Well monitoring stations (real-time network, climate response network, total active network) in the drought-stressed areas continued to show low groundwater levels. Streamflow (observed and modeled [CPC anomalies and percentiles, VIC 1-, 2-, and 3-month runoff percentiles]) was below average for the month across much of the Mid-Atlantic to Gulf Coast States and parts of the Southwest, Southern Plains, Ohio Valley, northwestern Great Lakes, coastal Pacific Northwest, and Hawaii.
February had a mixed temperature and precipitation pattern across Alaska, although most of the state was wetter than normal with February 2011 ranking as the 10th wettest February in the 1918-present record. Dryness in the southern portions of the state is reflected in the February precipitation pattern and mountain snowpack and SNOTEL station network snow water equivalent. The March 1st USDM map had a sixth of the state in the abnormally dry category, which was about half compared to last month and reflected February's above-normal precipitation. However, long-term deficits still remained at several stations at longer time scales (2, 3, 6, 12, 24, 36 months).
Most of Puerto Rico was drier than normal during February. This continued a trend which has been going on for the last 2 to 3 months. The dryness is not as widespread at longer time scales (last 6 months). Streamflow for Puerto Rico was near normal and the island remained drought free on the March 1st USDM map.
The rainfall pattern across the Hawaiian Islands was mixed during February. The area under severe (D2) drought shrank this month, compared to the end of January, but the area under moderate drought (D1) expanded, especially on the Big Island. Long-term rainfall deficits continued at many stations at several time scales, especially the longer time scales (last 2, 3, 6, 12, 24, 36 months), and February streamflow continued below normal on Maui and the Big Island.
On a statewide basis, February 2011 was drier than normal for many states in the Southwest, Southern Plains, Southeast, and Mid-Atlantic regions. Two states (Louisiana and Mississippi) had the 8th driest February in the 1895-present record. Dryness is evident for much of the last 12 months. The year-to-date (January-February 2011) was drier than normal for the southern half of the country and much of the West, with Virginia ranking 2nd driest, New Mexico 4th driest, and North Carolina 7th driest. This winter (December 2010-February 2011) was especially dry from the Mid-Atlantic to Southern Plains, with 11 states much drier than normal and 8 of those ranking in the top 10 driest category. Seven states in the Southeast ranked in the top 10 driest category for September 2010-February 2011, and 5 of them were in the top 10 driest category for the last 12 months (March 2010-February 2011).
Record dryness occurred for several climate divisions for the last several months:
Last 6 months (September-February):
Last 12 months (March-February):
The record dry March 2010-February 2011 followed a record wet March 2009-February 2010 in Arkansas climate divisions 8 and 9. Nine or 10 of the last 12 years had a very dry start (January-February) to the year in the piedmont areas of North Carolina (climate division 3) and Virginia (climate division 3). This is true on a statewide basis for these 2 states (North Carolina, Virginia) and on a regionwide basis for the Southeast region.
Percent area of the Western U.S. in moderate to extreme drought, January 1900-February 2011, based on the Palmer Drought Index.
The precipitation pattern over the West was mixed in February, with some areas wetter than normal and others drier than normal. On the whole, the western regions averaged near normal for the month. The February precipitation was not enough to overcome the dryness of January, with 2-month (January-February 2011) precipitation ranks still below normal for most western states. But heavy precipitation earlier in the season resulted in wetter overall conditions for winter (December 2010-February 2011) and the last 6 months (September 2010-February 2011). Water-year-to-date (October 2010-February 2011) precipitation was near normal in the Northwest, much below normal in the Southwest, and above normal in between. A similar pattern can be found in the mountain snowpack, snow water equivalent percentiles for SNOTEL stations, and snow water equivalent percent of normal for SNOTEL basins. An analysis of early data by the USDA indicated that reservoir levels were, on average, below normal from New Mexico, across the Interior Basin states, to Oregon, and near to above normal in Washington and Arizona and the Rocky Mountain states. According to the USDM, 15 percent of the West was experiencing moderate to severe drought at the end of February, slightly more than January, while the Palmer Drought Index statistic was about 9 percent, a slight drop compared to last month.
A more detailed drought discussion, provided by the NOAA Regional Climate Centers and others, can be found below.
As noted by the Southeast Regional Climate Center, mean precipitation for the Southeast region was slightly below normal in February, although there was much local variability. There were two relatively narrow corridors of above normal precipitation (125 to 150 percent), one that cut across the eastern Panhandle of Florida and one that stretched across southern Alabama, central Georgia, and eastern portions of the Carolinas. Much of this precipitation was tied to a series of storms that crossed the region on the 4th and 5th of the month. The driest locations (less than 25 percent of normal) were found in the southern half of Florida with some locations recording less than 5 percent of normal precipitation for the month. Most notably, Key West, Florida recorded only 0.01 inch (0.25 mm) of precipitation for the month, making it the second driest February in a record extending back to 1871. Elsewhere across the Southeast, monthly precipitation was generally between 50 and 75 percent of normal.
Mean temperatures were above normal across the Southeast in February. Mean temperatures were near normal across Puerto Rico, while the U.S. Virgin Islands experienced their fourth consecutive month of below normal temperatures. The cold weather that dominated the region in December and January continued into early February, particularly across parts of Alabama and Florida. However, temperatures rebounded significantly during the second half of the month as the Arctic Oscillation transitioned to a positive phase and more southerly and westerly winds became established over the Southeast. Despite a return to warm temperatures in February, mean temperatures during meteorological winter (December-February) ranked among the top 5 coldest in many locations across the region.
The lack of precipitation in February resulted in the emergence of severe (D2) and extreme (D3) drought conditions across the northern half of Alabama and southeastern Florida, respectively. However, the beneficial rains through portions of central Georgia and South Carolina resulted in a reduction from severe drought to moderate drought (D1) conditions in those areas. The warm temperatures near the end of the month caused many of the peach and blueberry crops to bloom across Georgia, making them especially vulnerable to a killing frost. According to the Georgia State Climate Office, a killing frost could have an economic impact of over $150 million to the industry. In addition to the warm temperatures, a combination of high winds, dry soils, ample leaf litter, and low relative humidity created ideal conditions for wildfires across much of the Southeast. In North Carolina, the Division of Forest Services reported over 12,000 fires across the state in February and more than 1,700 acres burned.
As explained by the Southern Regional Climate Center, with the exception of central and northern Arkansas, northern Tennessee and northeastern Oklahoma, the month of February was a dry month for the Southern region. The driest areas of the region included much of southern and southwestern Texas, where most stations received less than a quarter of the monthly normal precipitation total. In central Louisiana and southern Mississippi, the majority of stations reported precipitation totals that ranged between 25 and 50 percent of normal. Similar conditions were also observed throughout parts of central Texas and northwestern Oklahoma. The wettest area of the region included much of north central Arkansas where stations reported between 150 and 400 percent of normal precipitation. On February 9-10, 2011, many areas of Oklahoma received heavy snowfall accumulations. Accumulations varied from a few inches to over two feet in the northeastern portions of the state.
January average temperatures in the Southern region varied spatially from west to east. In the northwestern areas of the region, temperatures were generally 2 to 6 degrees F (1.11 to 3.33 degrees C) below the monthly normal. In Tennessee and Mississippi, however, temperatures averaged between 2 to 6 degrees F (1.11 to 3.33 degrees C) above the monthly normal. All state value temperature rankings fell within the two middle quartiles of the normal distribution as based on the 1895-2011 period of record.
Drier than normal conditions throughout most of the Southern region led to an expansion of drought in many areas. Most notably, there was an expansion of extreme drought in central and northern Louisiana and in eastern Texas. Southwestern Texas also experienced a slight expansion of extreme drought. On February 1, 2011, only 6.59 percent of the Southern region was experiencing extreme drought. One month later, on March 1, 2011, that number has increased to 10.76 percent. In Mississippi, the entire state was classified in moderate drought or worse. In fact, almost three quarters of the Southern region was in moderate drought or worse, compared to 58.97 percent of the region the previous month.
As summarized by the Midwest Regional Climate Center, Midwest February precipitation totals included pockets of below normal precipitation but also large areas exceeding 200 percent of normal. The below normal areas were extreme eastern Kentucky, southwestern Iowa, and the northern quarter of the region. The driest area was the upper Midwest were totals were less than 50 percent of normal. Snowfall totals were also quite variable in February. Below normal snowfall totals, as much as 50 percent below normal, occurred in southern Indiana, southern Ohio, and eastern Kentucky as well as across the upper Midwest. Snowfall totals were above normal with totals exceeding 200 percent of normal over swaths from southern Minnesota to southern Michigan and from Missouri to northern Ohio. Totals approached 700 percent of normal in southwest Missouri. Monthly records for snowfall were set in Chicago, Illinois, Galesburg, Illinois, Lansing, Michigan, and Flint, Michigan. Almost 900 daily snowfall records were set across the Midwest during the month. Winter season snowfall totals were above normal for nearly all of the Midwest. Slightly below normal totals fell in northern Michigan while totals exceeded 200 percent of normal in parts of the other eight Midwest states. More than 2900 daily snowfall records occurred during the three-month winter season. Winter season snowfall records were set in Peoria, Illinois and Rochester, Minnesota.
February temperatures varied in both time and space. The second week of the month was cold and the third week warm across the region. Weeks one and four varied spatially giving a mix of temperature departures for the month. Winter temperatures were near normal in northern Michigan and Wisconsin and below normal across most of the other Midwest states. February was the only winter month to report above normal temperatures for parts of the Midwest.
As noted by the Northeast Regional Climate Center, on average, the Northeast saw 119 percent of the normal precipitation amount, or 3.22 inches (81.8 mm). The three southernmost states were drier than normal with departures of 88 percent in West Virginia, 75 percent in Maryland, and 58 percent in Delaware. It was the 17th driest February in 117 years in Delaware. The states with above normal precipitation had departures that ranged from 104 percent in New Jersey to 143 percent in Pennsylvania, where it was the 17th wettest February since 1895. Precipitation totals for the region for climatological winter were exactly normal. The range of departures among the states was 68 percent of normal in Delaware to 122 percent in Maine. It was the 10th driest winter in Delaware and the 16th driest in Maryland. Drier than normal conditions in the southern part of the region have led to drought concerns there. The March 1, 2011 U.S. Drought Monitor indicated that parts of West Virginia, Maryland, Delaware and Pennsylvania were abnormally dry, while extreme eastern West Virginia was in moderately drought (D1). In addition, small areas in northern New York, Vermont, and New Hampshire were abnormally dry.
Temperatures in the Northeast averaged just below normal in February. The region's average of 25.6 degrees F (-3.6 degrees C) was -0.8 degrees F (-0.4 degrees C) below normal. It was the coolest February since 2007. The temperature average for the winter of 2010-2011 (December - February) was 24.2 degrees F (-4.3 degrees C), which was 2.0 degrees F (1.1 degrees C) below normal.
As explained by the High Plains Regional Climate Center, several storm systems affected the High Plains region this month. Overall, South Dakota, eastern Kansas, and pockets of both Colorado and Wyoming had precipitation which was above normal. The rest of the region had either near or below normal precipitation. A strong system brought extreme cold and snow to the region at the beginning of the month. Another round of snow hit the eastern portion of the region on February 8th-9th. The heaviest snow fell in eastern Kansas where up to 16 inches (41 cm) was reported. A mid-month warm-up allowed for much of the snow cover across the region to melt, however the snow cover quickly built up again. Later in the month a storm system moved through the region bringing thunderstorms, ice, and snow. On the 21st, thunderstorms occurred in eastern Nebraska while just to the north, ice accumulations up to a quarter inch were reported. Meanwhile, heavy snow fell across South Dakota, where over a foot (30 cm) of snow was reported in many locations. On February 24th another snow storm hit the region. Heavy snows of up to a foot (30 cm) were again reported in southwestern South Dakota and up to 5-9 inches (13-23 cm) were reported in Kansas and Nebraska. Also, in Kansas and Nebraska, much of the snow fell in a short amount of time and snowfall rates of 2 inches/hour (5 cm/hour) were reported.
The heavy snow this month not only led to new February records but also new winter (December-February) records. Bonner Springs, Kansas, which is just outside of Kansas City, recorded its snowiest February on record with 17.5 inches (44 cm) of snowfall (period of record 1938-2011). The old record was set in 1978 with 17.0 inches (43 cm). Aberdeen, South Dakota had its 4th snowiest February with 21.0 inches (53 cm) and its snowiest winter with 61.2 inches (155 cm) of snow (period of record 1893-2011). This beat the longstanding record of 57.0 inches (145 cm) which was set in 1915.
Meanwhile, North Dakota was on the dry side this month. Fargo, North Dakota received only 0.08 inch (2 mm) of liquid equivalent precipitation which was the 6th driest February on record and Grand Forks, North Dakota received only 0.04 inch (1 mm) of liquid equivalent precipitation which was the 4th driest February on record. The dry conditions this month did not stop the concern over flooding along the Red River or flood preparations. According to the North Dakota State Climate Office, Fargo had already filled 1.5 million sand bags and the North Dakota National Guard began training sessions to help prepare for the potential flooding.
February 2011 was a month of temperature extremes in the High Plains Region. The lowest temperatures of the month were, for the most part, observed at the beginning of the month. An arctic air mass settled into the Region and many daily low temperature records were set. Dangerous wind chills were also experienced throughout the Region. There was a warm-up mid month and daily high temperature records were broken in parts of Colorado, Kansas, Nebraska, and South Dakota but the month ended on the chilly side as cold air quickly moved back into the Region. Overall, February average temperatures were 2-6 degrees F (1.1-3.3 degrees C) below normal for most of the Region. The cold weather allowed many locations to break into the top 20 coldest Februaries on record. In addition, locations in Wyoming and the panhandle of Nebraska had average monthly temperatures which ranked in the top 10 coldest Februaries on record. Sunshine 3NE, Wyoming, which is located in the northwest part of the state, had its 2nd coldest February on record with an average temperature of 15.0 degrees F (-9.4 degrees C). The record of 11.0 degrees F (-11.7 degrees C) was recorded in 1989 (period of record 1963-2011).
The U.S. Drought Monitor did not change over the last month for the High Plains region. Severe drought conditions (D2) persisted over south-central Colorado and western Kansas. A large area of moderate drought conditions (D1) across eastern Colorado, western Kansas, and the panhandle of Nebraska also remained. A second area of D1 in southeastern Kansas also existed. In addition, the areas of abnormally dry conditions (D0) in western Wyoming and surrounding the D1 areas remained unchanged.
Upper Colorado River Basin: As reported by the Colorado Climate Center, the March 1st NIDIS (National Integrated Drought Information System) assessment for the Upper Colorado River Basin (UCRB) indicated that February was wetter than average for the Wasatch and Uinta Mountains in Utah, areas of southwestern Wyoming, the Sangre de Cristos in southern Colorado, and the northern mountains of Colorado. Many counties along the Front Range also saw above average precipitation for the month, although because February is not typically a wet month, their water-year-to-date numbers were still at a deficit. The valleys of western Colorado and eastern Utah, the Four Corners region, and the southeastern Plains remained dry for the month. The majority of the SNOTEL stations in the UCRB had high percentile rankings for water-year-to-date (WYTD) precipitation. The Rio Grande and San Juan basins in southern Colorado were the driest with percentile ranks below 50 percent. Some sites in the Rio Grande basin had percentiles below 30 percent. Snowpack around most of the UCRB was above average for this time of year. Normal streamflow was recorded at the end of the month at key gages around the basin. For the month of February, temperatures were below average for most of the UCRB and the eastern Plains of Colorado. Soil moisture was in good condition, with dry soils evident in eastern Colorado. The driest soils were in southeastern Colorado. For the month of February, most of the reservoirs saw their levels drop, with the exception of Lake Dillon, which saw a slight increase in its levels. Lake Powell volume decreased by over half a million acre feet since the beginning of the month, with inflows into the lake slightly below what had been projected. Lake Granby also had a larger decrease in volume, likely to prevent spilling from occurring this summer as its levels were very high at the end of February. Most of the reservoirs ere near or above average levels for this time of year. Lake Powell was at 73 percent of average, but it was expected to have rising levels as snowmelt starts in March and April.
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.
February weather systems brought periods of heavy rainfall to the Hawaiian Islands from Kauai to Maui. However, these systems weakened or moved away from the state before reaching the Big Island. As a result, moderate drought, or D1 category conditions in the USDM map, recently returned to the Big Island's eastern slopes and merged with the existing moderate drought area extending from South Point to leeward Kohala. Extreme drought, or D3 conditions, persisted in the Pohakuloa area. Conditions improved enough over leeward Maui to warrant a reduction of severe drought coverage. Severe drought, or D2 category, was limited to the area near Kihei from Kaonoulu to Kamaole. Improvements were also reported on Lanai which resulted in a change from a D2 to D1 depiction over the entire island. The drought status for Molokai remained unchanged over the past month.
Some drought impacts in Hawaii include the following:
- On Oahu, water levels in the Waimanalo reservoir continued to increase over the past month. However, the State of Hawaii Department of Agriculture maintained a 10 percent cutback in irrigation water use as a precaution.
- On Molokai, water levels in the Kualapuu reservoir remained relatively steady during the past month. Thus, the State of Hawaii Department of Agriculture has kept in place the mandatory 30 percent cutback in irrigation water consumption.
- On Maui, pasture conditions have been improving over the past month. The area from Kaonoulu to Kamaole near Kihei has not recovered enough to fully support cattle ranching operations. Water supply levels remained sufficient for upcountry Maui. However, as a precaution, the Maui County Department of Water Supply continued to request a 5 percent reduction in water use by upcountry residents. A 10 percent reduction in water use by central and south Maui residents also remained in effect.
- On the Big Island, dry conditions over the windward areas have started to produce impacts. Some farmers reported reduced corn, taro, and sweet potato yields due to lack of rainfall. Ranchers have been hauling water to support livestock. Pastures in areas that recovered from previous drought conditions were starting to deteriorate again. Some of the windward area residents on catchment systems have started to hire water hauling services due to below normal rainfall.
On other Pacific Islands, drought conditions continued near the equator as La Niña conditions persisted through February. There were signs that this mature La Niña has begun to weaken, but the westward extent of the drought-producing weather pattern (subsiding air and colder-than-normal sea surface temperatures) remained near 155 E longitude. February rainfall at Kapingamarangi was extremely low with only 0.20 inch, or 1.95 percent of normal. Severe drought conditions extended eastward from about 150 E longitude to beyond the international date line. This area includes Kapingamarangi Atoll, Nauru and the atolls of western Kiribati.
Monthly (February 2011) and 6-month (September 2010-February 2011) precipitation reports included:
- Pohnpei: 12.25 inches of rain in February (125 percent of normal) with September-February rainfall 92 percent of normal,
- Nukuoro: 6.66 inches for February (56 percent of normal) with September-February total at 53 percent of normal,
- Kapingamarangi: 0.20 inch for February (1.95 percent) with September-February at 15 percent of normal,
- Kosrae: 10.96 inches for February (85 percent) with September-February at 81 percent of normal.
Three-month (December 2010-February 2011) percent of normal rainfall reports included:
- Chuuk: 93 percent
- Guam: 143 percent
- Kapingamarangi: 11 percent
- Koror: 125 percent
- Kosrae: 75 percent
- Kwajalein: 124 percent
- Majuro: 121 percent
- Nukuoro: 41 percent
- Pohnpei: 95 percent
- Saipan: 111 percent
- Yap: 113 percent
In the Federated States of Micronesia, adequate rainfall has occurred for most of Pohnpei state and in Kosrae state. Drought conditions remained at Kapingamarangi. The atoll has been extremely dry since August 2010. The overall persistence of this event, along with computer forecast models and past climate history, suggest that this dry pattern should begin to decrease in intensity very slowly during March. Continued implementation of water conservation measures on Kapingamarangi was encouraged. Rainfall at Nukuoro has been variable but probably sufficient for drinking, cooking and most agriculture. Other islands of Pohnpei state have had more than sufficient rainfall. Damage to food crops has likely occurred on Kapingamarangi Atoll as a result of the drought. Some wells and numerous individual solar stills were still producing water for drinking and cooking.
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.|
|southeast u. s.||west north central u. s.||south u. s.|
|southwest u. s.||northwest u. s.||west u. s.|
|Contiguous United States|
- 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
- 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
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