A swath of precipitation (0.5 to 1.5 inches) this past week led to small improvements from parts of Oklahoma and Arkansas northeastward to the Central Appalachians.
Since the major drought that affected the Central Appalachians and Upper Ohio Valley peaked in late September, drought has steadily improved across these areas the past two months. Near to above-normal precipitation during the past 30 days supported drought improvement across parts of the Northeast.
Farther to the south across the Southeast, Lower Mississippi Valley, and Texas, 30 to 60-day precipitation deficits continue to increase with expanding and intensifying drought during mid to late December. December is typically a drier time of year for the Upper Midwest and Northern to Central Great Plains where little to no weekly drought change was warranted.
Since the beginning of October, precipitation has generally averaged below normal across the Central Rockies, Great Basin, Southwest, and southern California. From Dec. 17 to 23, enhanced onshore flow resulted in wetter-than-normal conditions across coastal northwestern California and much of the Pacific Northwest. The 7-day temperatures, ending on Dec. 23, averaged above normal throughout the West and Central to Southern Great Plains with colder-than-normal temperatures limited to the Great Lakes and Northeast.
The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the U.S. Department of Agriculture and the National Oceanic Atmospheric Administration. (Map courtesy of NDMC.)
South
Based on increasing short-term precipitation deficits and 30 to 90-day SPIs, abnormal dryness and moderate drought were expanded across northern Louisiana and portions of south-central Mississippi.
These same indicators along with the NDMC short-term blend supported the expansion of D1 to severe drought across portions of eastern and southern Texas. Around 1 inch of precipitation supported a 1-category improvement across portions of Arkansas and central to southeastern Oklahoma.
Midwest
Across ongoing drought areas of the Midwest, precipitation was light (0.5 inch or less, liquid equivalent) and no change was needed in Dx categories.
High Plains
Based on SPIs at various time scales, low snowpack, and the NDMC short-term blend, a 1-category degradation was made to northern Colorado along with southern and northwestern Wyoming.
Snow water equivalent amounts are below the 5th percentile where extreme drought was expanded in Wyoming. These same indicators justified an expansion of abnormal dryness across southwestern Colorado. Severe drought was expanded across western Nebraska due to soil moisture percentiles falling below the 10th percentile and support from the 90 to 120-day SPI.
West
As of Dec. 23, snow water equivalent was below-normal across the Northern Rockies of Montana and Wasatch Mountains of Utah.
Looking ahead
During late December, multiple low pressure systems will bring heavy precipitation (rain and high-elevation snow) to the Pacific Northwest and northern California. On Dec. 27, widespread rain with locally heavy amounts (more than 2 inches) is forecast for eastern Oklahoma, eastern Texas, and Arkansas.
The Climate Prediction Center’s 6- to 10-day outlook (valid Dec. 30 to Jan. 3) favors above-normal temperatures across the East, southern Great Plains, and Southwest. Near normal temperatures are favored for the northern Great Plains, Northern Rockies, and Pacific Northwest as above-normal temperatures are forecast to moderate during this 5-day period.
A pattern change is forecast during the first week of the New Year with a transition toward near or below-normal temperatures for much of the lower 48 states. Elevated above-normal precipitation probabilities are forecast for the Pacific Northwest, Great Plains, Midwest, and Northeast.
Below-normal precipitation is more likely for the southern two-thirds of California and the Southwest.
Brad Pugh is with the National Oceanic Atmospheric Administration and the Climate Prediction Center.
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