This week’s drought summary: High pressure dominated the southern half of the contiguous U.S. (CONUS) again during this U.S. Drought Monitor (USDM) week. Upper-level weather systems tracked across the U.S.-Canadian border, dragging surface lows and fronts along with them. The high brought hot temperatures to much of the South, East, and West, with daily maximum temperatures exceeding 90 degrees F every day. The fronts brought cooler temperatures to the Upper Midwest at the beginning of the week, but maximum temperatures began to exceed 90 degrees across the Plains and eastward as the week wore on.
The hot temperatures increased evapotranspiration (ET) which dried soils and stressed crops and other vegetation. This was seen in ET models such as the EDDI and ESI and several soil moisture models, satellite observations of soil moisture, and agricultural field reports. As noted by the U.S. Department of Agriculture (USDA) on July 27, 50% or more of the topsoil moisture was short or very short (dry or very dry) in states across the Northeast, Midwest, Southeast, southern Plains, southern to central Rockies, and Far West. For the nation as a whole, 37% of the topsoil moisture and 35% of the subsoil moisture was short or very short, and 30% of the pasture and rangeland was in poor to very poor condition.
Drought or abnormal dryness expanded or intensified across parts of the West, Midwest, Southeast, and Northeast where little to no rain fell and 30- to 90-day precipitation deficits mounted. But locally heavy rainfall was generated by the fronts in parts of the Plains, Midwest, and East. Heavy rain also fell across southern Texas when Hurricane Hanna struck, and Hurricane Douglas graced parts of Hawaii with beneficial rain. Where the rain fell on drought or abnormally dry areas in these regions, contraction occurred.
South: Central Oklahoma was inundated with heavy frontal rain while Hanna brought heavy rain to the Gulf Coast from Soutg Texas to Mississippi. Rainfall exceeded three inches in these areas, with locally heavier amounts. Parts of Arkansas, Tennessee, and North Texas received an inch or more of rain. But little to no rain occurred in a large swath from Southwest Texas to Western Tennessee and Northern Mississippi. Abnormal dryness and moderate to extreme drought contracted, especially in Central Oklahoma and the Texas Panhandle. Abnormal dryness contracted in parts of Tennessee and Louisiana while abnormal dryness also expanded in parts of Eastern Oklahoma and parts of Arkansas, Mississippi, and Tennessee. Abnormal dryness and moderate to extreme drought expanded in other parts of Texas.
Looking ahead: For July 30 to Aug. 3, the ridge of high pressure shifts to the West with a trough setting up in the upper atmosphere over the eastern half of the CONUS. Little to no rain is forecast for most of the West, with half an inch or less across parts of the Rockies and only a couple inches stretching across the middle of New Mexico. But an inch or more of rain is expected from the central Plains to southern Appalachians and southern Great Lakes, with heavy rain (four inches or more) widespread from Missouri and northern Arkansas to Kentucky, Indiana, and western North Carolina.
A tropical system is predicted to sideswipe the East Coast, dumping an inch or more of rain across Florida to the Mid-Atlantic states, three or more inches over southern Florida, and up to two inches over eastern North Carolina and southeast Virginia.
Half an inch or less of rain is expected from Texas to Southwest Georgia, and across the Northern Plains to the Western Great Lakes. In the Northeast, predicted precipitation amounts range from nearly two inches in Western New York to a tenth of an inch along coastal New England. The ridge will keep temperatures warmer than normal in the West while the trough brings cooler-than-normal temperatures to much of the CONUS east of the Rockies.
The outlook for Aug. 4 to Aug. 8 calls for a greater than average chance of wetter-than-normal conditions along the East Coast, in the Northern Plains, across Deep South Texas, and most of Alaska. Odds favor drier-than-normal conditions across most of the West, the Southern Plains, the Central Gulf of Mexico coast to the Great Lakes, and over North Alaska. Warmer-than-normal temperatures are likely across the Southwest and along the immediate East Coast, while cooler-than-normal temperatures are likely to dominate from the Plains to Appalachians, in the Pacific Northwest, and across most of Alaska.