According to today's Drought Monitor report of the U.S. Department of Agriculture (USDA), a powerful low-pressure trough developed in the upper levels of the atmosphere over the eastern contiguous U.S. (CONUS) during this U.S. Drought Monitor (USDM) week (December 21-27). At the surface, the trough was associated with a strong cold front that poured frigid arctic air into the U.S. east of the Rockies. Daytime maximum temperatures in the northern Plains were well below zero degrees Fahrenheit, with minimum temperatures colder than 20 below zero, at the peak of the cold wave.
In the Midwest, parts of Minnesota and Iowa received up to half an inch of precipitation this week, while an inch to more than 2 inches fell in favored snowbelt areas to the lee of the Great Lakes in Michigan. The rest of the Midwest received less than half an inch, with the driest areas over southwestern portions of the region.
The precipitation amounts were above normal in parts of Minnesota, Iowa, Wisconsin and Michigan, while the rest of the region was drier than normal for the week. Moisture surpluses eliminated the spot of D1 in northern Wisconsin, but the deep freeze locked conditions in place in Iowa and Minnesota where no changes were made. D0 and D1 were expanded in Indiana, Illinois, Ohio, and Lower Michigan, and D0 expanded in eastern Missouri, based on several indicators. These indicators include dry soils, low streamflow, and mounting precipitation deficits, especially as seen in the 1- to 12-month Standardized Precipitation Index (SPI).
For the full USDA report for Dec. 29, click here.