Map released April 29, 2021 | Data valid April 27, 2021
This week’s drought summary: Several upper-level troughs and closed lows moved in the westerly jet stream flow across the contiguous U.S. (CONUS) during this U.S. Drought Monitor week. They dragged surface fronts and low pressure systems along with them. The weather systems moved across the West then generally followed two storm tracks after crossing the Rockies – one track was along the Canadian border, while the other track was along the Gulf Coast states. As a result, above-normal precipitation fell across parts of the West, much of the Gulf Coast from eastern Texas and Oklahoma to Georgia, parts of the Mid-Mississippi Valley, and parts of the northern Great Lakes and Maine. Precipitation amounts were generally 0.5-2.0 inches in the West where precipitation fell but exceeded two inches across a large part of the Gulf Coast states. The rest of the CONUS had below-normal precipitation for the week.
A swath from New Mexico to Lower Michigan, and parts of the northern Plains and Far West, had little to no precipitation. With upper-level troughs and surface cold fronts dominating the circulation pattern, weekly temperatures averaged below normal across most of the CONUS.
Drought or abnormal dryness contracted in parts of the Southern Plains to Southeast, where heavy rains fell, and in parts of the Northern Plains and Northeast, where overall conditions warranted improvement. But drought or abnormal dryness expanded or intensified across parts of the West, Midwest, other parts of the Plains, and the Carolinas, as well as much of Hawaii and Puerto Rico. In these areas, precipitation deficits grew and soils continued to dry. These changing conditions were reflected in several drought indices and indicators, including the Standardized Precipitation Index (SPI), streamflow and groundwater levels, soil moisture measurements on the ground and from satellite as well as soil moisture models, vegetation-based indices such as VegDRI, and mountain snow water content (SWE) in the West.
South: In the Southern Plains, the western half of Texas and Oklahoma were dry this week, with little to no rain falling. But a half inch or more of rain was widespread across the rest of the South, with 2+ inches in streaks across eastern Oklahoma and Texas, Arkansas and Louisiana, and southern Mississippi. D0-D3 contracted in East Texas, D0-D2 contracted in parts of Oklahoma, D1 disappeared and D0 contracted in Louisiana. But further west, D0-D4 expanded in South and Southwest Texas and D0 expanded in Western Oklahoma. Dry or very dry soils grew in area to 67% of Texas and 29% of Oklahoma, according to USDA statistics, and 43% of the winter wheat crop in Texas was in poor to very poor condition. In the Midland-Odessa area, 2020-2021 had the driest 13-month April-April period on record, and the fourth driest any 13-month period ever (behind 2011 which had the top three driest 13-month periods). Falling levels of the Edwards Aquifer triggered water restrictions in several Texas communities, including San Antonio, New Braunfels, and San Marcos.
Looking ahead: A large low pressure trough moving out of the Southwest triggered areas of rain across parts of the southern and central Plains into the Midwest, and another system spread precipitation across the Northeast, as the new USDM week began. During April 29-May 3, another Pacific system will move into the country. These weather systems are forecast to spread an inch or more of precipitation across the southern Plains, Lower to Mid-Mississippi Valley, Tennessee and Ohio Valleys, southern Great Lakes, and Northeast. Bands of heavy precipitation – three inches or more – are expected across Texas to Arkansas and along the Ohio River. An inch or more of precipitation is projected to fall across parts of northeast Colorado, Wyoming, and northwest Washington. Half an inch or less of precipitation should fall across the Southeast from Florida to Virginia, New Mexico to the Central Plains, the rest of the Great Lakes, and Central to Northern Rockies. No precipitation is forecast to fall over much of the Northern Plains and most of the rest of the West. Temperatures are predicted to be near to above normal for the week across the CONUS.
The outlook for May 4-8 shows drier-than-normal weather is favored for much of the West to Great Plains with wetter-than-normal conditions for most of the Mississippi River to East Coast region. Warmer-than-normal weather is likely across most of the western, southern, and East Coast states, except for the Mid- to Upper-Mississippi Valley, Great Lakes, and New England. Odds favor wetter-than-normal weather for southern Alaska and cooler-than normal weather for most of the state.