A series of Pacific upper-level weather systems, and their associated surface lows and fronts, moved across the contiguous U.S. (CONUS) during this U.S. Drought Monitor (USDM) week. These systems dropped half an inch or more of precipitation across much of the West, Plains, and Midwest, as well as parts of the Northeast. Heavy rains of 2 to 4 inches, or more, fell across parts of California, especially the upslope regions. The systems triggered severe weather in the Plains, with training thunderstorms dropping flooding rains. Two inches or more of precipitation was measured from northern Texas to Illinois, parts of the northern Plains, eastern Texas to Louisiana, and Upper Mississippi Valley to western Great Lakes. Parts of Oklahoma to southeast Kansas saw more than 5 inches of rain. Precipitation was sparse in southern Arizona and New Mexico, and across most of the Southeast where high pressure dominated, with less than a tenth of an inch observed. Most of the precipitation fell on areas that were drought-free. Drought and abnormal dryness contracted in parts of the Southwest, but expanded in areas that received below-normal precipitation this week, had continued and prolonged precipitation deficits, or were experiencing drought impacts. These included parts of southern Texas, the Pacific Northwest, the northern Plains, the Southeast, Hawaii, Puerto Rico, and the southern parts of the Alaskan panhandle. With the elimination of D2 from New Mexico, this week is the first time in the history of the USDM that the CONUS has been free of Severe to Exceptional Drought. However, it also marks the first time that Extreme Drought (D3) has been analyzed for Alaska.
Next week (May 23-28) will largely see a repeat of this week’s weather pattern. A couple upper-level Pacific weather systems will move across the West, then roar out of the Southwest, across the Plains, to the Great Lakes, dropping several inches of rain across parts of the southern to central Plains and Midwest. Half an inch to locally 2 inches of precipitation are expected across much of the West, except little to no precipitation is forecast for southern portions of the Southwest and parts of the Pacific Northwest. The weather systems will keep western temperatures cooler than normal, while the North Atlantic High will keep temperatures warmer than normal across the southeastern third of the CONUS. Little to no precipitation is predicted for much of the southern Plains to Southeast, although the western Carolinas might see up to an inch. Over an inch of precipitation is expected for northern portions of the Northeast, while southern portions should receive half an inch or less. For May 29-June 5, more of the same. Odds favor cooler-than-normal temperatures from the Southwest to Great Lakes and southern coastal Alaska, while warmer-than-normal temperatures are expected for the Southern Plains to Mid-Atlantic region, the West Coast to northern Rockies, and much of Alaska. Odds favor below-normal precipitation for the Gulf of Mexico and Southeast coastal states, Washington and Oregon in the Pacific Northwest, parts of New Mexico, the North Dakota and Minnesota D0 areas, and southern Alaska panhandle. Odds favor wetter-than-normal conditions for the rest of Alaska, the rest of the West, and most of the Great Plains to Northeast.
The storm systems left western portions of the Midwest wetter than normal, but much of the Ohio Valley to eastern Great Lakes, as well as a strip along northern Minnesota, were drier than normal. Like the Northeast, most of the Midwest has seen prolonged long-term wet conditions. But persistent dryness in northwest Minnesota for the last 7 days to 24 months resulted in the introduction of D0. Parts of Kentucky extending into western Tennessee have also been drier than normal for the last 7 days to 2 months. This area remained free of drought and abnormal dryness this week, but it will be watched for possible D0 if the rains don’t return.