An atmospheric river brought heavy rain and high-elevation snow across part of the West, leading to drought improvements in California, the Pacific Northwest, the northern Rockies and the Great Basin. Drought in the High Plains remains largely unchanged; much of the excess moisture is tied up in snowpack and its effects on soil moisture and groundwater recharge remain to be seen. Drought expanded across parts of the South where short-term moisture deficits on top of longer-term drought continue to build.
South
Much of Oklahoma and Texas missed out on this week’s precipitation events, resulting in the expansion of drought. In Oklahoma, temperatures averaged 10 to 13 degrees above normal over the previous 2 weeks while precipitation has been less than 50% of normal over the past 4 months. Extreme (D3) drought expanded in response to well-below-normal (10th percentile or lower) measurements of streamflow, groundwater and soil moisture conditions. Texas also saw a swath of degradations from the north-central region to South Texas where short-term moisture deficits, on top of longer-term drought, have continued to build, and streamflow, soil moisture and groundwater levels range from below (10th to 24th percentile) to well below normal (10th percentile or lower). In the eastern part of the region, last week’s rainfall erased lingering areas of abnormal dryness.
Midwest
The Midwest saw a mix of drought improvement and expansion last week. Heavy precipitation (150 to over 300% of normal) in Ohio and Indiana led to improvements in moderate (D1) drought and abnormal dryness (D0) where streamflows and soil moisture show signs of recovery. Missouri, though, saw an expansion of severe (D2) drought based on increasing precipitation deficits (6 to 12 inches over the last 6 months) and declining streamflows. Continued below-normal precipitation led to an expansion of D0 in Illinois and far southeast Wisconsin as streamflows have begun to decline.
High Plains
Much of the High Plains remained in a holding pattern last week. Areas that received abundant snowfall over the Water Year are slow to make improvements due to the long-term nature of drought in the region. Until spring melt shows verified evidence of soil moisture and groundwater recharge, it will be difficult to tell how much effect snow has had on drought conditions. Severe (D2) drought improved in eastern North Dakota, which has received 16 to 20 inches of snow this season. No areas deteriorated significantly, except for areas of abnormal dryness (D0) in South Dakota and Colorado.
West
Heavy precipitation helped erase areas of abnormal dryness in parts of Washington, Oregon, western Wyoming, western Colorado, Arizona and New Mexico. The only places in the West seeing an expansion of drought were Oregon and Colorado.
