December 2010 Drought Report

Overview

December 2010 was near the long-term average (54^th driest and 44^th coolest, based on data back to 1895) when weather conditions are averaged across the country. But this reflected wide regional extremes (monthly precipitation and temperature) which resulted from the persistence of weekly regional precipitation (weeks 1, 2, 3, 4, 5) and temperature (weeks 1, 2, 3, 4, 5) anomalies throughout the month. Beneficial precipitation fell across the Hawaiian drought areas, and abundant rain and snow pummeled much of the West, but the month was drier than normal across much of the drought areas of the southern and central Plains, Southeast, and Ohio Valley. Abnormally dry and drought conditions contracted across parts of the Ohio Valley, Northeast, Far West/Intermountain Basin, and Hawaii, but expanded in the Central and Southern Plains, Southeast, and Southwest.

The U.S. Drought Monitor drought map valid December 28, 2010.

A strong west-to-east flow in the jet stream circulation characterized the weather pattern over the contiguous United States for December 2010. Deep low pressure systems developed in this flow, resulting in intense winter storms across the nation and outbreaks of cold Canadian air, especially east of the Rockies. About a third of the country was covered in snow at the beginning of the month. The snow cover expanded and contracted throughout the month with the passage of several winter storms, reaching 39 percent coverage by December 6^th, about 53 percent by the 19^th, and 55 percent by the 27^th. By the end of the month, more than 8 feet of snow covered higher parts of the Sierra Nevada, with moisture content more than twice normal for this time of year. December 2010 was the 7^th snowiest December for the contiguous U.S. and for the North American continent, based on satellite observations of area covered that go back to 1966. The storm systems triggered deadly tornado outbreaks at the end of the month in the Midwest to Lower Mississippi Valley.

A pineapple express (atmospheric river) of moisture flowed into the U.S. from the Pacific for much of the month, bringing rain and snow to much of the West and northern Plains. Nevada and Utah had the wettest December in the 116-year record, Minnesota 4^th wettest, North Dakota 5^th wettest, and California ranked 7^th wettest. Heavy rains from the atmospheric river brought drought relief to Hawaii, but the weather systems were deflected away from Alaska, which had a colder- and drier-than-normal December.

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, which were dominant during November, continued in December. The first was the La Niña, which is the phenomenon created by cooler-than-average sea surface temperatures in the eastern tropical Pacific Ocean. La Niña is typically associated with wet conditions in the northern tier states and Ohio Valley this time of year, and warm and dry conditions in the southern tier states. The second atmospheric circulation index was the Arctic Oscillation (AO), which was negative during most of December and strongly negative during the last half of the month. A negative AO is typically associated with dry conditions in the Southeast (especially the Southern Plains to Lower Mississippi Valley) and colder-than-normal temperatures east of the Rockies at this time of year (November-January).

The temperature and precipitation pattern for December 2010 matched what is expected from the negative Arctic Oscillation, especially east of the Rockies. Florida and Georgia had the coldest December in the 1895-2010 record and the Carolinas (N, S) ranked 3^rd coldest. A total of 11 states from the Ohio Valley to the Gulf Coast had the tenth coldest, or colder, December in 2010. Precipitation was below normal from the Southern Plains and Southeast to the southern Great Lakes, with Louisiana and Mississippi having the 3^rd driest December and 4 other states ranking in the top ten driest category. As a result, drought expanded in the southern tier states, especially the Southern Plains and Southeast. By the end of the month, 24 percent of the contiguous U.S. was classified in moderate to extreme drought, according to the USDM. The precipitation pattern over the West reflected a combination of La Niña and Arctic Oscillation influences.

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

• parts of Hawaii, where conditions improved but moderate (D1) to extreme (D4) drought persisted;
• the Southern Plains to Southeast, where moderate (D1) to extreme (D3) drought expanded;
• the central Plains, where moderate to severe drought expanded;
• the Ohio Valley, where moderate (D1) to extreme (D3) drought contracted; and
• the Arrowhead of Minnesota and parts of the West, where moderate drought lingered.

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 December 2010 much of the Southern Plains, Southeast, and Ohio Valley, and southern parts of the Great Lakes and Southwest. Wet conditions are evident on the Z Index map across the northern Plains and much of the West. These moisture anomalies persistently built up throughout the month (Palmer Z Index map for December 10, 15, 20, 25, 31). Compared with the November 2010 PHDI map, the December 2010 PHDI map indicates that drought conditions intensified in the Southeast, Lower Mississippi Valley, and Ohio Valley; drought conditions lingered in parts of the Mid-Atlantic region; and wet conditions intensified in the West and Northern Plains. The November 2010 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, Lower Mississippi Valley, Ohio Valley, and around Delaware is both a short-term and long-term phenomenon, and that the dryness in the Southern and Central Plains is a short-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 the Central and Southern Plains at 1-, 2-, and 3-month time scales, and in southern portions of the Southwest for most time scales from 1 to 24 months. The Southeast to Lower Mississippi Valley are very dry from 1 to 12 months, with some evidence of dryness even at 24 months. Dryness in the Ohio Valley is evident at 1, 3, and 6 months, while the parts of the Great Lakes are dry at 1 to 3 months. Mid-Atlantic coast dryness shows up to some degree in the 1-month to 12-month maps. Wet conditions dominated the Northern Plains and parts of the Northeast at all time scales and much of the West for the last 1 to 12 months.

Agricultural Indices

December 2010 NLDAS ensemble-mean model soil moisture anomalies for the top 1 meter of soil

Vegetation Drought Response Index (VegDRI), December 26, 2010

Abnormal dryness and drought were evident in several indicators. There were hardly any days with rain from the Southern Rockies to the Southern and Central Plains, much of Florida, and parts of northern Minnesota and the Mid-Atlantic to southern New England states. This resulted in long runs of consecutive dry days in some of these areas. It is also reflected in low total precipitation amounts and below-normal precipitation. On the other hand, it rained or snowed most days of the month along northern parts of the Pacific coast. 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, NLDAS [North American Land Data Assimilation System] top soil layer and total soil layer, VIC [University of Washington Variable Infiltration Capacity macroscale hydrologic model]), was still drier than average across much of the country from the southern Great Lakes to the Lower Mississippi Valley, across most of the Gulf Coast, and across parts of the central and southern Rockies and Plains. Satellite monitoring of vegetation health (Vegetation Drought Response Index [VegDRI] [December 26, January 2], Vegetation Health Index [VHI]) indicated stress on vegetation in parts of the Southwest, southern Plains, and Southeast.

Hydrological Indices

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-, 3-, 9-month]) was below average for the month across much of the Southeast and Gulf Coast and parts of the Great Lakes, Central Plains, Southwest, Mid-Atlantic coast, and Hawaii.

Regional Discussion

The U.S. Drought Monitor drought map valid December 28, 2010.

Below-normal precipitation fell across most of Alaska during December 2010. Consequently, snowpack was below normal in the southern basins and the snow water content of many of the SNOTEL Network stations and Alaskan river basins decreased compared to last month. The December 28^th USDM map had a fifth of the state in the abnormally dry category to reflect long-term deficits which still remained at several stations at longer time scales (2, 3, 6, 12, 24, 36 months).

Much of Puerto Rico was drier than normal during December and November-December, with deficits also showing up for the water year-to-date (October-December). But they mostly disappear at longer time scales (last 6 months and annual). Streamflow for Puerto Rico was near normal and the island remained drought free on the December 28^th USDM map.

Above-normal precipitation fell across most of the Hawaiian Islands during December, with heavy rainfall in the northern islands. This brought significant improvement to the drought conditions, with exceptional drought disappearing and the percentage of the state in moderate to extreme drought falling from 49 percent at the end of November to 36 percent at the end of December. However, long-term deficits continued at many stations at several time scales (last 2, 3, 6, 12, 24, 36 months). December streamflow was below normal on the southern islands.

On a statewide basis, December 2010 was drier than normal for many states in the Southern and Central Plains, Southeast, Mid-Atlantic, Ohio Valley, and southern Great Lakes. Five states had the tenth driest, or drier, December in the 1895-2010 record, including Louisiana and Mississippi which each ranked third driest. December was record dry for several climate divisions in the Lower Mississippi Valley (Louisiana climate divisions 1, 2, and 3, and Mississippi climate divisions 7, 8, and 10).

Dryness in the Southern Plains and Southeast to Ohio Valley has persisted for much of the last three months. Seven states had the tenth driest, or drier, October-December in 2010, with Florida ranking as the driest in the 1895-2010 record. October-December 2010 was record dry for several climate divisions in the southern regions (Texas climate divisions 5 and 10, and Florida climate divisions 2, 3, 4, and 5). Florida also had the driest July-December on record.

The Lower Mississippi Valley has suffered from deficient precipitation for most of the last 12 months. Statewide, Louisiana had the fifth driest year in the 1895-2010 record, Arkansas ranked ninth driest for 2010, and Mississippi eleventh driest. It was the driest year on record for several climate divisions (Louisiana climate divisions 2, 3, and 4, Mississippi climate division 4, and Arkansas climate division 8).

Percent area of the Western U.S. in moderate to extreme drought, January 1900-December 2010, based on the Palmer Drought Index.

December 2010 was wetter than average across much of the West. The wet December, combined with unusual wetness in November and October, has given the West a very wet start to the hydrologic year (October through the following September), both at the low elevation stations as well as the high elevation SNOTEL Network stations. Several feet of snow has fallen at the higher elevation SNOTEL stations of the Sierra Nevada, Cascade, and Rocky Mountain ranges. Mountain snowpack water content was at near-record levels for this time of year at many stations from California to Colorado, as well as on a basin-wide basis, and at record levels in eastern Nevada. Snow water content was lowest in the Southern Rockies, northeast Wyoming, and northern portions of the Pacific Northwest, with the southern and eastern portions of the Southwest having significantly below-normal water-year-to-date precipitation. An analysis of early data by the USDA indicated that reservoir levels were generally mixed, with levels near to above normal in the northern Rockies states and Arizona, but near to below normal in the Pacific Northwest states and parts of the Southwest and Great Basin. According to the USDM, 12 percent of the West was experiencing moderate to severe drought at the end of December, an increase compared to November, while the Palmer Drought Index statistic was about 4 percent.

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, monthly precipitation was below normal (generally less than 50 percent) across nearly the entire region in December. A large portion of the monthly rainfall came on the 1^st of the month as a line of strong storms moved through the Southeast and mid-Atlantic regions. The driest locations across the Southeast (less than 25 percent of normal) were found in central and eastern Florida, southern Alabama, central portions of Georgia and the Carolinas, much of the southern Appalachian Mountains, and the Shenandoah Valley of Virginia. Sanford, Florida, located northeast of Orlando, recorded 0.15 inch (3.8 mm) of precipitation for the month, which was only six percent of normal. Montgomery, Alabama [1.03 inches (26.2 mm)] and Columbus, Georgia [1.56 inches (39.6 mm)] experienced their 2^nd driest December in records extending back to 1871 and 1947, respectively. In contrast, monthly precipitation totals were between 150 and 300 percent of normal across the northern coast of Puerto Rico. San Juan recorded 7.47 inches (189.7 mm) of precipitation for the month, which was 2.9 inches (73.7 mm) above normal. It was the driest year on record in the Jacksonville Beach, Florida area with a preliminary annual total of 28.44 inches (722.4 mm). Conversely, San Juan, Puerto Rico recorded its wettest year on record with 89.51 inches (2274 mm), eclipsing the previous record of 87.55 inches (2224 mm) set in 1931.

Monthly average temperatures for December 2010 were well below normal across the Southeast region. The greatest departures occurred throughout Florida and eastern sections of Georgia, the Carolinas, and Virginia, where monthly average temperatures were 9 to 11 degrees F (5.0 to 6.1 degrees C) below normal. Interior portions of the Southeast were generally 6 to 9 degrees F (3.3 to 5.0 degrees C) below normal, while much of Alabama and northern Virginia were 5 to 6 degrees F (2.8 to 3.3 degrees C) below normal. Over 70 locations in the Southeast experienced their coldest December on record. Across the Southeast, over 1,100 daily low maximum temperature records and over 800 daily minimum temperature records were tied or broken during the month. Jacksonville, Florida recorded 19 days of subfreezing minimum temperatures during the month, which shattered the old record of 12 set back in 2000. The frigid air masses that predominated across the Southeast also influenced parts of the Caribbean; monthly average temperatures were below normal across Puerto Rico and as much as 4 degrees F (2.2 degrees C) below normal on the U.S. Virgin Islands.

Despite the overall lack of precipitation during the month, the coverage of abnormally dry (D0) and drought conditions (D1 or greater according to the U.S. Drought Monitor) across the Southeast decreased from 87 percent at the end of November to 77 percent at the end of December. Areas of abnormal dryness (D0) were eliminated across parts of Virginia, western and eastern North Carolina, western Alabama, and northeast Georgia. In addition, moderate drought (D1) conditions expanded slightly into parts of central North Carolina and south Florida, while extreme drought (D3) conditions expanded across northeast Florida and southeast Georgia. The cold temperatures severely disrupted the planting of winter vegetables (e.g. peppers and onions) in parts of Florida and Georgia and resulted in a state of emergency declaration in Florida to ensure that the harvesting and transport of fall crops were not delayed on account of the cold weather.

As explained by the Southern Regional Climate Center, December precipitation totals were quite low over most the Southern region. For the majority of the region, this was the third consecutive dry month. In December, the majority of the region received less than half of the monthly normal precipitation. Louisiana reported a state average monthly total of only 1.85 inches (46.99 mm), which is the third driest December on record (1895-2010). Likewise, Mississippi experienced its third driest December on record with a monthly precipitation total of only 1.45 inches (36.83 mm). Arkansas also reported a monthly precipitation total of 1.45 inches (36.83 mm), which makes it their eighth driest December on record. Texas recorded its eleventh driest December, with a monthly precipitation total of 0.67 inches (17.01 mm). Tennessee reported its eighteenth driest December, while Oklahoma reported its thirty-first driest December. The state average precipitation total in Tennessee was 2.76 inches (70.10 mm), while Oklahoma reported a value of 0.93 inches (23.62 mm). The driest areas of the Southern region included much of western Texas, southern Texas, northern Louisiana, and southern Arkansas. In these areas, most stations reported less than a quarter of the monthly normal precipitation totals. In the case of west and southern Texas, many stations recorded less than one tenth of an inch (2.54 mm) for the month. December average daily temperatures varied spatially throughout the Southern region, with a strong gradient from west to east. The western states experienced a slightly warmer than normal month, while eastern and central states experienced a much cooler than normal month.

A third consecutive month of dry conditions in the Southern region has resulted in a wide expansion of drought conditions. As of December 28, 2010, 67.65 percent of the Southern region was experiencing moderate drought or worse; 35.21 percent was in severe drought or worse, and 10.17 percent was classified as extreme drought conditions. This is a dramatic change from November. For instance, on November 30, 2010, the aforementioned values were 41.2 percent, 19.3 percent, and 2.7 percent, respectively. The most significant changes are seen in the central counties of eastern Texas where extreme drought was introduced. There was also a westward expansion of severe drought into the western parishes of Louisiana.

As summarized by the Midwest Regional Climate Center, Midwest precipitation totals varied widely in December. Above-normal precipitation fell in the northwest quarter of the region with west-central Minnesota receiving nearly five times their normal precipitation. Eastern Kentucky was also slightly above normal. The areas in between received less than normal precipitation with a swath from Missouri to Lake Huron at less than half of their normal. Snowfall was especially heavy in Minnesota, western Wisconsin, and northeast Iowa. Above-normal snowfall also fell along a narrow swath extending from southern Minnesota to eastern Kentucky. Three different storms tracked along this path during the month. 2010 annual precipitation was above normal for most of the western half of the Midwest with south-central Iowa more than 20 inches (508 mm) above their normal for the calendar year. Southeast Missouri and along the Ohio River to Cincinnati were 6 inches (152 mm) to 10 inches (254 mm) below normal for their 2010 annual precipitation.

December temperatures were colder than normal across the Midwest. Departures from normal ranged from 0 °F (0 °C) in the upper Midwest to as much as 10 °F (6 °C) below normal in eastern Kentucky. Maximum temperatures were even colder ranging from 1 °F (1 °C) to 14 °F (8 °C) below normal. Kentucky recorded its first colder-than-normal month since February 2010. The year was near normal for most of the Midwest with only the northern parts of Minnesota, Wisconsin, and Michigan averaging 2 °F (1 °C) to 4 °F (2 °C) above normal.

As noted by the Northeast Regional Climate Center, December's precipitation totals varied throughout the region, with 5 states averaging drier than normal and 7 states on the plus side. The regional average was 3.82 inches (97 mm), which was 113 percent of normal. Once again, Maine was the wettest state in the region, with 175 percent of the normal amount of precipitation. Delaware, with only 42 percent, had its 10^th driest December since 1895. Annually, precipitation totals evened out, leaving the region at exactly 100 percent of normal. Yearly departures among the states ranged from 87 percent of normal in Delaware to 115 percent in Maine.

Temperatures during December 2010 averaged below normal for the first time since December 2009. The Northeast's monthly average of 25.4 degrees F (-3.7 degrees C) was 3.0 degrees F (1.7 degrees C) below normal and 2.4 degrees F (1.3 degrees C) cooler than December 2009. It was the coldest December in the region since 2000. A cool December could not offset the previous eleven months of above normal temperatures. With an annual average of 49.2 degrees F (9.6 degrees C), 2010 became the 5^th warmest year in the Northeast since recordkeeping began in 1895. Two states, New Hampshire and Rhode Island, had their warmest year on record. Of the remaining states, all but West Virginia had annual temperature averages that placed them in the top 20 warmest since 1895.

As explained by the High Plains Regional Climate Center, southern portions of the region, including Kansas, Nebraska, and eastern Colorado, received little to no precipitation in December. This caused existing drought conditions to persist and led to the development of drought in eastern Kansas as well. While the southern portion of the region remained dry, several storm systems impacted the northern portions this month. The Dakotas were hit particularly hard by heavy snowfall which set new records and impacted travel. Several areas of both North Dakota and South Dakota had liquid equivalent precipitation totals which were over 400 percent of normal. Temperatures across the High Plains region this month were below normal in the eastern half and above normal in the western half. The dividing line between the above and below normal temperatures ran from southwestern South Dakota into central Nebraska, and then into west-central Kansas.

According to the USDM, drought conditions deteriorated across the southern portions of the region this month. By the second week of December, abnormally dry conditions (D0) had expanded north from Oklahoma into eastern Kansas and severe drought conditions (D2) had expanded from eastern Colorado into western Kansas. In addition, D0 had spread further east in Nebraska. By the end of the month, moderate drought conditions (D1) had developed in eastern Kansas as well. Only slight improvements were seen in extreme northwestern Colorado where the D0 area was eliminated and in western Wyoming where the D1 and D0 areas were trimmed due to heavy snowfall.

As summarized by the Western Regional Climate Center, precipitation was well above normal throughout the region except for Southern Arizona and New Mexico and Eastern Colorado. Many parts of southern and central California received their wettest December ever. It was the second wettest December on record in downtown Los Angeles dating back to 1889. Bishop, California, received 105 percent of their annual average in 3 days (18-20^th). Up to 29 inches of rain in the San Gabriel and San Bernardino Mountains of Southern California for the month, most of it within a 6-day period from the 17^th-22^nd. Bakersfield's (California) total of 5.82 inches (148 mm) not only broke a December record but an all-time monthly record going back to 1893. New December records were also set in portions of Southern Nevada and Utah. St. George Utah had their wettest December on record dating back 117 years. Over 15 inches (381 mm) of precipitation fell at Mt. Charleston, Nevada, while Ely, Nevada recorded their wettest and snowiest December in 85 years of data. Snowpack in the Sierra Nevada of California and a broad swath northeast to the upper Colorado River Basin was over 200 percent of normal by the end of the month, and the rest of the West except Washington was reporting a snowpack of well over 100 percent. Meanwhile, in Honolulu, rainfall for December was the greatest since 1987 (11.73 inches, 298 mm) and provided 67 percent of their 2010 annual total. Much of that (5.41 inches, 137 mm) fell in one day (on the 19^th). Except for Montana, nearly the entire West observed above normal temperatures, especially southeast New Mexico and the Front Range of Colorado. Fairbanks, Alaska, on the other hand, had its coldest December since 1980. Had it not been for extremely cold temperatures the final two days of the month, many locations would probably have broken records for December warmth.

Upper Colorado River Basin: As reported by the Colorado Climate Center, the late December-early January NIDIS (National Integrated Drought Information System) assessment for the Upper Colorado River Basin (UCRB) indicated that most of the Upper Colorado River Basin (UCRB) received near or above average precipitation for November, while areas east of the UCRB remained dry -- a pattern that continued through December. As of December 28^th, all of the sub-basins of the UCRB had above average snowpack and precipitation for the current water year (October 1-December 28), with only a few individual sites slightly below average. Most of the western portions of the UCRB had snow water content near the 100^th percentile, meaning that very few to no years have been as wet by this time as the current water year. Averaged across the UCRB, water-year-to-date (WYTD) precipitation was at 147 percent of average and snowpack was at 142 percent of average. As of December 26^th, about 92 percent of the USGS streamgages in the UCRB recorded normal (25^th to 75^th percentile) or above normal 7-day average streamflows. While recent flow conditions have been good, total cumulative runoff from the upper basin to the lower basin for the 2010 calendar year will be substantially less than the historical average. For the month of December, temperatures were around 6 degrees F warmer than average through much of the UCRB. While temperatures have been warm, the air has been moist with a persistent flow of moist Pacific air for most of the month. Soil conditions improved in northeastern Utah, the Four Corners region and western Wyoming, but soils dried east of the UCRB throughout eastern Colorado. Reservoir levels were above average for this time of year at Blue Mesa, Flaming Gorge, Navajo Lake, and Lake Granby. Lake Powell's storage decreased in December, with its lake level at 77 percent of average for this time of year and around 60 percent of capacity.

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.

Drought conditions eased significantly across most of Hawaii during December. Kauai County and Oahu received the highest rainfall totals, eliminating drought in both areas. While the Big Island received lower amounts of rainfall, improvements were most significant here and included the elimination of exceptional drought (D4). Exceptional drought conditions were in place since March 2, 2010. The area of extreme drought (D3) was also reduced significantly and covered just the upper leeward slopes from Ahumoa to Pohakuloa. Severe drought (D2) surrounded the D3 area and extended northwestward to Kawaihae and southwestward into the central Humuula Saddle. A separate area of severe drought covered the southern portion of the Kau District from Manuka to Naalehu. For Maui County, areas of D3 conditions in Lanai, western Molokai, and leeward Maui have all been changed to D2 conditions. East Molokai and the windward portions of Maui were free of drought.

Some drought impacts in Hawaii include the following:

• Water levels in the Waimanalo Reservoir on Oahu increased considerably over the past month. The State of Hawaii Department of Agriculture eased water use restrictions, going from a mandatory 30 percent cutback to a 20 percent cutback on December 21.
• Pastures and general vegetation conditions on Molokai have improved due to recent rainfall. Water levels in the Kualapuu Reservoir increased modestly but not enough to warrant any easing of the 30 percent cutback in irrigation water consumption.
• Above-normal rainfall produced an improvement in conditions on Lanai. Previously, drought conditions forced cattle ranchers to ship feed from off-island which resulted in financial impacts.
• Pastures in leeward Maui improved over the past month but more rainfall is needed for a full recovery. 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, pastures in the lower slopes of the South Kohala District and the southern portion of the Kau District improved during December. However, some ranchers were still hauling water to support livestock. Additional rainfall is needed in the coming months to produce a full drought recovery.

On other Pacific Islands, drought conditions continued near the equator. Although adequate rain from showers and occasional thunderstorms have occurred north of 3 degrees North latitude, strong subsidence associated with the moderate to strong La Niña has suppressed rainfall in areas closer to the equator. Drought conditions extended from about 150 degrees East longitude to at least the International Date Line. This area includes Kapingamarangi Atoll, Nauru, and the atolls of western Kiribati.

In the Federated States of Micronesia, adequate rainfall has occurred for most of Pohnpei state, but weather has remained very dry at Kapingamarangi over the last 5 to 6 months (Kapingamarangi is a southern island in Pohnpei state, near the equator). Kapingamarangi received only 0.76 inch of rain in December, which is 9 percent of average. The total rainfall for August-December 2010 was 7.81 inches, or 24% of average. Some damage to food crops may have occurred on Kapingamarangi Atoll as a result of the drought, so close monitoring of the health of food crops was recommended. Continued implementation of stringent water conservation measures on the island was also encouraged. Rainfall at Nukuoro was barely sufficient in December with only 3.85 inches, or 35 percent of average. For August-December, Nukuoro has received 40.13 inches of rain (73 percent of average). At Kosrae, December rainfall was 10.99 inches (72 percent) and August-December rainfall totaled 53.98 inches (79 percent). The statewide average for Pohnpei was 80 percent of normal for December and 87 percent of normal for August-December.

• 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
  • hydrologic year precipitation
  • snow water equivalent of snowpack
• 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

• The U.S. Drought Portal