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.
Half an inch to locally 2 inches of precipitation fell across parts of the Northeast, with the northern portions being wetter than normal. The southern half of the Northeast was drier than normal, with the driest areas being western New York and extreme southeast Pennsylvania. Wet conditions have dominated most of the Northeast for the last several months, so the region was free of abnormal dryness or drought.
The week was drier and warmer than normal across the Southeast. Coastal sections from North Carolina to Georgia have had precipitation deficits mounting for the last 4 months. D0 expanded in the eastern Carolinas and western Georgia. D1 expanded in parts of Georgia; reports have been received of slim grazing in Bleckley County, drying soils in Sumter, Terrell, and Dougherty Counties, and wilting corn in Terrell County. D0 was added to parts of Alabama. The soil hydrology in Alabama is characterized by poor water holding capability; as a result, this time of year the vegetation requires significant amounts of moisture which can quickly dry out soils during a 10-day stretch of no rain. There were reports that shallow rooted vegetation was already under stress in the dry areas of Alabama. According to May 19th reports from the U.S. Department of Agriculture (USDA), topsoil moisture was deteriorating across the Southeast, with the percent of the state experiencing short to very short (dry to very dry) soil moisture conditions increasing from 4% of Alabama last week to 12% this week; from 16% of Florida last week to 42% this week; from 20% of Georgia last week to 41% this week; and from 13% of South Carolina last week to 48% this week. Subsoil moisture was short to very short for 9% of Alabama, 33% of Florida, 22% of Georgia, and 34% of South Carolina.
Much of Oklahoma and parts of Texas to the Lower Mississippi Valley were wetter than normal this week, but southern and eastern portions of the region were drier than normal. Parts of north central Tennessee and western and southern Texas have been drier than normal for the last 60 to 90 days, but otherwise wet conditions dominate the region. Spots of D0 were added to western Texas along the Rio Grande River, southern Texas, and Mississippi and Tennessee where they connect to Alabama.
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.
Half an inch to over 2 inches of precipitation fell across much of the High Plains region this week. But there were some strips which received 0.25 inch or less, including parts of eastern Nebraska, northern North Dakota, southwestern Wyoming, and southeastern Colorado. D0 expanded in the northern counties of North Dakota. Soil moisture in northwest North Dakota was dry and planting has been slow, with the dry soils expected to delay planting further and delay germination; fire d