Map released: May 7, 2020 | Data valid: May 5, 2020
This week’s drought summary: A strong cold front progressed southeast across the Great Plains, Mississippi Valley, and Southeast on April 28 and 29. This cold front was a focus for a severe weather outbreak from Oklahoma and East Texas east to the middle and lower Mississippi Valley. As this front shifted south, heavy rain (more than two inches) fell from the western Gulf Coast east to the Florida Big Bend and Florida Gulf Coast. A summer-like ridge of high pressure aloft led to an early and persistent heat wave across southern California and the Desert Southwest during late April into early May. Much above normal temperatures also affected the southern Rockies and southern Great Plains. To the north of this upper-level ridge, multiple low pressure systems along a nearly stationary front resulted in occasional thunderstorms with locally heavy rain (one inch or more) to the Central Great Plains, middle Mississippi Valley, and Ohio Valley. Onshore flow led to a wet start to May across the coastal Pacific Northwest, but little to no precipitation was observed across the Great Basin.
South: Heavy rain (widespread amounts of more than two inches) at the end of April prompted a one-category improvement to parts of the western and northern Gulf Coast, including southern Louisiana and Southeast Texas. This recent heavy rain resulted in precipitation surpluses during the past 30 days and normal (25th to 75th percentile) 28-day streamflows.
However, dating back six months, large precipitation deficits (more than eight inches) remain across southeast Louisiana and the along the Mississippi Gulf Coast. In contrast to the improving conditions across Southeast Texas, drought coverage and intensity remained nearly steady or worsened slightly across South Texas.
Abnormal dryness (D0) was expanded across the Texas Panhandle and Northwest Oklahoma due to increasing 30-to 60-day precipitation deficits, above normal temperatures (highs well into the 90s and low 100s), and periods of strong winds during late April into the beginning of May. These indicators along with impact reports (poor pastures, low ponds, and poor winter wheat quality) support the introduction of a small D1 area in Northwest Oklahoma.
Looking ahead: On May 7 and 8, a low pressure system is forecast to track rapidly east across the Central and Eastern U.S. with a swath of moderate rainfall (0.5 to 1 inch) across the central Great Plains, middle to lower Mississippi Valley, Ohio Valley, and mid-Atlantic. Behind this low pressure system, much below normal temperatures are forecast to overspread the East-Central U.S. with at least a light freeze likely across the Great Lakes and eastern Corn Belt. Frost may extend south to the Shenandoah Valley and southern Appalachians. This late frost and/or freeze could damage vegetation in areas where the growing season has started. Meanwhile, a wave of low pressure is expected to develop along the tail end of a stationary front which could bring beneficial rainfall to southern Florida. The early and prolonged heat wave is forecast to ease across the Desert Southwest during the second week of May.
The CPC 6-10 day outlook (May 12-16) indicates that unseasonably cool temperatures are likely to persist into mid-May across the Corn Belt and much of the Eastern U.S. A cooling trend is forecast across the Western U.S., although above normal temperatures remain favored across the Southern Rockies and Southern Great Plains. The largest probabilities of above normal temperatures are forecast across Alaska. The evolving upper-level pattern favors above normal precipitation across much of the Great Plains and Mississippi Valley. These increased chances of above normal precipitation also cover much of the West.