Weather Summary: A strong upper-level ridge of high pressure continued to dominate the nation’s weather this U.S. Drought Monitor (USDM) week, bringing well above-normal temperatures to much of the country east of the Rockies. Beneath the core of the high, hot and dry weather baked the central and southern Plains to Ohio Valley. Monsoon showers and thunderstorms brought areas of rain to the West, cool fronts moving along the high’s northern edge triggered scattered showers and thunderstorms in the northern tier states, and a front skirting the high dropped beneficial rain along its eastern and southern peripheries. July 22 U.S. Department of Agriculture (USDA) reports indicated that 55 percent of the nation’s pasture and rangeland was in poor to very poor condition, breaking last week’s record. In the Plains and Midwest states, crop losses mounted, ranchers liquidated herds, and trees continued to drop leaves and branches. On July 25, USDA Secretary Tom Vilsack designated 76 additional counties in six states as drought disaster areas, bringing the total for the 2012 crop year to 1369 counties across 31 states. Over two dozen large wildfires were burning by the end of the USDM week – most in the West but several in the Plains.
The Northeast and Mid-Atlantic: Light to locally moderate rain fell across parts of the region. The rains were generally enough to keep the drought depiction status quo, although enough fell to dent D0 and D1 in northern Maryland. D1-D2 expanded across the Chesapeake Bay and into northern Virginia where rains were below-normal, and D0-D1 expanded in southern New England which experienced subnormal precipitation and widespread low stream levels. According to USDA statistics, 80 percent or more of the topsoil was rated short or very short of moisture in New York, Vermont, Massachusetts, and Connecticut, and half or more of the pasture and rangeland was rated poor or very poor in Delaware, Pennsylvania, and New York.
The Southeast, Deep South, and Southern Texas: Areas of beneficial rain, locally over three inches, fell from the central Appalachians to Tennessee Valley, central to coastal North Carolina, the Lower Mississippi Valley, and parts of western Florida. D0-D2 were pulled back from West Virginia to Tennessee, extreme northern Alabama, northwest Georgia, and parts of North Carolina, and D0-D1 were reduced in Louisiana and Mississippi. But the showers and thunderstorms were spotty, with many areas getting below-normal rainfall or hardly any at all. D0 expanded in southern and northeastern Florida, D1 was added to the southern coast of North Carolina and expanded in the Florida panhandle, and D1-D4 expanded in parts of Alabama and Georgia.
The Great Plains to Midwest: Frontal showers and thunderstorms dropped locally an inch or more of rain over parts of the Dakotas, Upper Mississippi Valley, and southern Great Lakes. In the Dakotas and Minnesota it was enough to slightly trim a few of the drought areas, but the 2+ inches from southern Wisconsin to northern Indiana was able to only maintain status quo. Most other areas were not as lucky. Pasture, rangeland, and crop condition continued to deteriorate from the Colorado High Plains to the Ohio and Mid-Mississippi valleys, and from Oklahoma to the Dakotas. Temperatures reached 100 degrees Fahrenheit or hotter across parts of the Great Plains to Midwest every day this week, and some locations have not had significant rain for the last 30 days. July 22 USDA statistics indicated over 90 percent of the topsoil was short or very short of moisture in Oklahoma, Kansas, Nebraska, Missouri, Iowa, Illinois, Indiana, and Ohio, with virtually all (99 percent) short or very short in Missouri and Illinois. Over 80 percent of the pasture and rangeland was in poor or very poor condition in Kansas, Arkansas, Missouri, Illinois, and Indiana. Corn, Soybean, Sorghum, and Alfalfa losses continued to mount, ponds dried up, and wells failed in several of the states. D0-D4 expanded region-wide.
The West: Monsoon showers dropped locally an inch or more of rain to parts of the West, but amounts were mostly less than half an inch. D3 was eliminated in extreme southern Arizona, D2 and D3 were pulled back slightly in parts of New Mexico, and D0 shrank in western Montana. But D3 expanded in western Nevada and D0-D2 grew in central to northern California (mostly in the San Joaquin Valley). Over 80 percent of the topsoil was rated short or very short of moisture in New Mexico, Colorado, and Wyoming. Three-fourths (75 percent) or more of the pasture and rangeland was classified as poor or very poor in California, Nevada, New Mexico, and Colorado.
Hawaii, Alaska and Puerto Rico: The precipitation pattern was mixed over Alaska this week, with drier-than-normal amounts observed at the northern, southeastern interior, and most panhandle stations, and above-normal precipitation at most stations to the west. It was a drier-than-normal week at most Hawaiian stations, but drought conditions were consistent with the existing depiction. Locally 2 to 5 inches of rain fell over parts of Puerto Rico this week. The D0 in western Puerto Rico was eliminated due to a re-evaluation of long-term conditions, but otherwise the depiction over Puerto Rico, Hawaii, and Alaska remained unchanged from last week.
Looking Ahead: Forecast models for July 25-30 show a front piercing the upper-level high early in the period, bringing scattered showers and thunderstorms to Great Plains and Midwest core drought area. Rainfall amounts may reach an inch in places, with a few locations receiving possibly 2 or more inches. The heaviest amounts from the front and low pressure system are expected to be in the Upper Great Lakes and Northeast, where locally 3 inches or more of rain may fall. Parts of the South could see an inch or more of rain as the front makes its way to the Gulf Coast. Monsoon showers could drop up to an inch of rain, total, across the Four Corners states, and frontal rains in the Northern Rockies could bring scattered light showers, but the rest of the West should be dry. Temperatures may dip from the frontal passage, but the week should average warmer than normal for most of the country.
For July 31-August 8, dry weather is expected to dominate from the West Coast to Northern Rockies, and from the Central to Southern Plains. Above-normal precipitation is forecast for the Southwest and from the Upper Mississippi Valley to Ohio Valley, parts of the Southeast, and from the Mid-Atlantic states to coastal Northeast. Above-normal temperatures are expected for much of the country, especially the Rockies and Plains states, while below-normal temperatures may hug the West Coast. Western Alaska is forecast to be wetter than normal, northern Alaska warmer than normal, and the southern areas cooler than normal.
Author: Richard Heim, National Climatic Data Center, NOAA
D0 ... Abnormally Dry ... used for areas showing dryness but not yet in drought, or for areas recovering from drought.
Drought Intensity Categories
D1 ... Moderate Drought
D2 ... Severe Drought
D3 ... Extreme Drought
D4 ... Exceptional Drought
Drought or Dryness Types
S ... Short-Term, typically <6 months (e.g. agricultural, grasslands)
L ... Long-Term, typically >6 months (e.g. hydrology, ecology)