Nationwide
A strong ridge of high pressure maintained its grip across the central part of the contiguous U.S. (CONUS) during this U.S. Drought Monitor (USDM) week (August 21-27). It was responsible for warmer-than-normal temperatures that stretched across the Plains and into the Upper Midwest.
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Upper-level troughs of low pressure dominated the West and East coasts, keeping weekly temperatures cooler than normal on both ends of the country. Pacific weather systems spread above-normal precipitation over northern California to the Pacific Northwest as they moved through the western trough, then triggered bands of thunderstorms over the Rockies and central to northern Plains as they bumped up against the ridge. Between the West Coast and Rockies rain areas, the West was dry from southern California to northern Montana. Rain developed along a stationary front that was draped across Florida. But the week was drier than normal for most of the CONUS east of the Rockies, with little to no rain falling from western Texas to the Mid-Atlantic Coast. The ridge migrated eastward as the week ended, so warmer-than-normal temperatures spread into the Midwest and Southeast.
Abnormal dryness and drought expanded and intensified across the southern Plains, Tennessee, and Lower Mississippi Valleys in a rapidly developing flash drought situation, and parts of the Southeast, Mid-Atlantic, Midwest, northern Plains, and Far West. Exceptional drought (D4) developed in parts of Ohio and West Virginia for the first time in the 25-year USDM history.
The West
Most of the West region was cooler than normal, with temperatures more than 10 degrees below normal across interior portions, especially in Nevada; eastern areas were warmer than normal, up to 6 or more degrees above normal in eastern Montana and eastern New Mexico.
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More than 2 inches of rain fell over coastal parts of northern California, southern Oregon, and northern Washington, with 0.5 to 2 inches over large parts of the Four Corners states. The rain that fell was not enough to make up for deficits accumulated over several months to more than a year, so no improvement to the depiction was made. Abnormal dryness expanded in Nevada and southern California, where little to no rain fell this week, and moderate to extreme drought expanded in Montana.
According to USDA statistics, half or more of the topsoil moisture was short or very short in Montana (82%), Oregon (77%), Idaho (68%), Washington (64%), New Mexico (62%), and Nevada (55%), and half or more of the subsoil moisture was short or very short in Montana (82%), Oregon (72%), Nevada (70%), Idaho (64%), Washington (63%), and New Mexico (63%). Half or more of the pasture and rangeland were rated in poor or very poor condition in Oregon (64%), Washington (60%), and Arizona (52%).
The High Plains
Weekly temperatures were warmer than normal across most of the High Plains region, ranging from near to 2 degrees below normal in western Colorado to 6 to 10 degrees above normal in parts of Nebraska and the Dakotas.
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Thunderstorm complexes moved across parts of the region, dropping 2 to 3 inches of rain locally. In many cases, the storms were localized, with one part of a county receiving rain and another part getting nothing—this was the case in other parts of the country as well. Drought or abnormal dryness contracted in a few areas of Colorado, Kansas, Nebraska, and South Dakota but expanded or intensified in parts of all of the High Plains states.
USDA statistics indicate half or more of the topsoil is short or very short in Wyoming (73%), Colorado (52%), and Kansas (52%), and half or more of the subsoil is short or very short in Wyoming (81%) and Kansas (57%).
The South
Hot and dry conditions continued for the South region this week. Western parts of Texas and Oklahoma were the epicenter of the heat, with weekly temperatures averaging 6-10 degrees above average, with local areas even warmer.
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In the east, Arkansas, Mississippi, and Tennessee, the average temperature is 2 to 4 degrees cooler than normal. Parts of coastal Texas to the state’s interior received half an inch to locally 2 inches of rain, but this mostly fell in drought-free areas. Most of the South region had no rain this week. Abnormal dryness and moderate to severe drought expanded in all states, while extreme drought expanded in Texas and developed in Oklahoma, Mississippi, and Tennessee. The heat and dryness of this August have resulted in flash drought conditions. Summer last year was a period of record and near-record heat and dryness. These extreme conditions of these two periods have combined to overwhelm the wet conditions during the intervening months.
More than half of the topsoil and subsoil moisture was short or very short across all states, with Texas leading at 72% of the subsoil and 81% of the topsoil so rated. More than 70% of the topsoil was short or very short in Louisiana (77%) and Mississippi (72%), and more than 60% was rated in Arkansas (63%) and Tennessee (64%). In Texas, 41% of the cotton crop and 58% of the pasture and rangeland were in poor to very poor condition.
Drought impact reports in Oklahoma included desiccated fields, dry ponds, a high risk of wildfires, and low reservoir levels in the southwestern part of the state. In Tennessee, drought impacts include pastures providing little to no feed, drying or dried up ponds, creek levels very low, and complete or near crop failure. In Mississippi, four counties have burn bans, pastures in the state’s northern half are no longer producing grass for cattle, and soils are so dry they no longer can support vegetation. — UNL Drought Monitor
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