5/10 Drought Monitor - Some Spot Improvements, But "Dramatic" Expansion Of Level 4 In TX, OK, NM

National Drought Summary -- May 10, 2011

The discussion in the Looking Ahead section is simply a description of what the official national guidance from the National Weather Service (NWS) National Centers for Environmental Prediction is depicting for current areas of dryness and drought. The NWS forecast products utilized include the HPC 5-day QPF and 5-day Mean Temperature progs, the 6-10 Day Outlooks of Temperature and Precipitation Probability, and the 8-14 Day Outlooks of Temperature and Precipitation Probability, valid as of late Wednesday afternoon of the USDM release week. The NWS forecast web page used for this section is: http://www.cpc.ncep.noaa.gov/products/forecasts/.

South Atlantic Seaboard and Eastern Gulf Coast States: Many locations from central South Carolina northward through south-central Virginia recorded 0.5 to 2.0 inches of rain last week, as did parts of west-central and southeast Florida. This precipitation was of some limited benefit, and resulted in no improvement in Drought Monitor classifications.

Through the remainder of the region from Virginia southward through Florida and southwestward through Mississippi, only light precipitation was observed, if any. As a result, the Drought Monitor classifications deteriorated, particularly along and near the Gulf Coast, where surface moisture declined markedly. Exteme drought (D3) was introduced in part of southeastern Georgia, and extended slightly southward along the southeastern coast of Florida. Severe drought was expanded to include southeastern Alabama, the western Florida panhandle, most of the southern half of Georgia, and coastal east-central Florida. In addition, abnormally dry conditions expanded northwestward in northeast Georgia and western South Carolina. For the last 3 months, rainfall was 8 to locally more than 12 inches below normal across southern sections of Mississippi and Alabama, and through the western Florida panhandle.

Lower Mississippi Valley: Although little or no precipitation fell across this region, a review of current and forthcoming conditions led to drastic improvements in parts of Louisiana. Rainfall has been markedly below normal throughout the southern half of the state on time scales ranging from 3 to 12 months or more; however, any effects from these deficits are quickly fading along the Mississippi and Atchafalaya Rivers as well as the wetlands that cover much of the southeastern parts of the state, where major to historic flooding is anticipated in some areas. Water levels were rising as of this writing in a large swath covering areas from the Atchafalaya River Basin eastward through areas immediately adjacent to the Mississippi River, and major to historic floodwaters will encroach on these areas through the next 7 days or more. Also, increasing water levels through most of southeastern Louisiana to the west and south of Lake Pontchartrain have relieved or soon will relieve any drought effects that had been felt there.

Meanwhile, a sharp gradient exists between these areas of flooding or wetland and lands that are typically dry to the west, north, and east. From these parts of Louisiana through most of the rest of the state, drought remains a serious issue, and conditions persisted or worsened last week. D1 to D4 conditions prevailed, with the most serious drought covering west-central Louisiana, where large moisture shortfalls date back well over a year. Generally 10 to 15 inches of rain fell during the last six months, which was 12 to locally 20 inches below normal. The D4 area expanded slightly eastward last week, and D3 conditions pushed into southwestern Louisiana; otherwise, drought severity was essentially unchanged.

Central and Southern Plains: Only a few isolated sites in this region recorded any measurable rainfall last week as drought intensified in many areas. Some improvement was introduced in northeastern Texas and immediately adjacent sections of Oklahoma and Louisiana based on a re-assessment of the effects of the prior week’s rainfall. Throughout the rest of the region, large areas of drought intensification were introduced as a result of another dry week. D1 to D2 conditions expanded northward and eastward in Kansas, but conditions were much worse farther south, where D4 conditions dramatically expanded across southwestern Oklahoma, large parts of Texas, and southeastern New Mexico. Precipitation over the last 90 days was 8 to 12 inches below normal throughout southeastern and east-central Texas, and in parts of southeastern New Mexico, no measurable precipitation has been recorded for the last 3 to (in a few isolated spots) 6 months.

The drought has brought a variety of serious impacts to much of the region. Water supplies are declining, and in a few areas water restrictions have been imposed, across the southwestern half of Texas and southeastern Oklahoma. Fire danger has been extremely high for repeated and extended periods in areas from south-central New Mexico and the Big Bend of Texas northeastward, occasionally reaching as far as southwestern Kansas, adjacent Colorado, and the western Oklahoma Panhandle. So far this year, wildfires have consumed more than 2 million acres in Texas alone.

In addition, agriculture has been seriously affected. In Texas, 76 percent of the winter wheat crop was in poor or very poor condition in Texas, according to the National Agricultural Statistics Service, as was 50 percent of the crop in Colorado and 41 percent in Kansas. Pastures and rangelands have also experienced serious impacts because of the drought. About 79 percent of such areas were in poor or very poor condition across New Mexico, as were 77 percent in Texas, 49 percent in Oklahoma, and 48 percent in Colorado.

The Southwest: Precipitation was negligible to non-existent last week in southwestern Colorado, most of Arizona, and western New Mexico last week; however, normal amounts are quite low this time of year, so the D0 to D3 areas remained unchanged.

Hawaii, Alaska, and Puerto Rico: Several inches of precipitation fell on the Alaskan panhandle last week, with more modest totals, generally less than an inch, reported in the remainder of the abnormally dry region. D0 conditions remained unchanged from last week.

Heavy precipitation, exceeding 5 inches in a few spots, fell on portions of the Big Island last week. This precipitation, considered in conjunction with the substantial rainfall observed in many areas during prior weeks, led to a reduction in extent and severity of the D0 to D3 conditions that had enveloped central and western sections of the island. D3 conditions were eliminated in the northern reaches, and significant reductions in the coverage of D0 to D2 conditions occurred in northern and eastern parts of the dry regions. The only exception was in the northeastern parts of the island, where slowly increasing moisture shortfalls led to the development of abnormally dry conditions.

Farther northwest through the islands in the central part of the state, only light precipitation was observed, and areas of dryness and drought remained unchanged.

Looking Ahead: During May 12 - 16, 2011, moderate to locally heavy rains will fall on some currently-dry parts of the country. The heaviest amounts, 1 to 2 inches, are forecast for central and northeastern Colorado and much of Nebraska. In addition, beneficial rains of 0.5 to 1.5 inches are expected away from the coast in eastern Texas and across northern and western Louisiana. Generally 0.5 to 1.0 inches are anticipated in the dry areas along the Atlantic Seaboard, though less is expected in most of Florida. Other areas shouldn’t expect much in the way of relief. Less than 0.5 inch is expected along the Gulf Coast, and at most one-quarter of an inch is forecast from roughly the westwern halves of Kansas, Oklahoma, and Texas westward through New Mexico and Arizona.

The outlook for May 17 - 21, 2011 brings enhanced chances for above-normal precipitation the dry areas in the Carolinas and Virginia, across southern Florida, and in the Great Plains from central Texas northward through eastern Colorado and Nebraska. In contrast, the odds favor below-median precipitation along the central Gulf Coast, and from the southwestern and western tiers of Texas westward through most of New Mexico. In addition, the entire state of Alaska has enhanced chances for sub-median precipitation. In other currently-dry sections of the country, neither abnormally wet nor abnormally dry conditions are favored, and essentially no forecast is made for these areas.

Author: Rich Tinker, NOAA/NWS/NCEP/CPC

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