An atmospheric river of Pacific storm systems slammed parts of the West Coast with heavy precipitation during this U.S. Drought Monitor week (February 14-20). The weather systems dried out as they crossed the western mountains, then produced anemic precipitation amounts east of the Rockies. Parts of the Midwest and Northeast received limited precipitation amounts from passing cold fronts.
A few areas received half an inch of precipitation, but most of the Midwest region saw only a couple tenths of an inch. Dry conditions over the last 1 to 6 months prompted the expansion of D0-D2 in Michigan and Wisconsin and D1 in southeast and northeast Minnesota. The lack of snow (“snow drought”) in Minnesota has had a sizable impact on winter recreation. D0 expanded slightly in northwest Iowa.
D0 was expanded in the Dakotas, and D1 expanded in North Dakota, where the last 3 months have been dry and the lack of snow cover has exposed bare ground.
Temperatures were 6 to 9 degrees above normal in northern parts of the region this week. The Midwest has experienced unusually warmer-than-normal temperatures during the last 1 to 2 months, with the last month averaging 6 degrees above normal along the Ohio Valley to over 15 degrees above normal in Minnesota. Since this is winter, vegetation is dormant and evapotranspiration is minimal. But in the weeks ahead, if the anomalous warmth persists as the region transitions into spring, evapotranspiration will increase, soils will dry, and the effects of the moisture stress, if rain isn’t sufficient, will need to be reflected in the USDM depiction.
For much of the next 2 weeks, the atmospheric circulation is expected to consist of an upper-level trough over the western CONUS and a ridge over the eastern two-thirds of the country, with Pacific weather systems migrating through the trough/ridge pattern.
National Drought Mitigation Center – University of Nebraska-Lincoln
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