Midwest Overview - February 2004

February 2004 temperatures averaged above normal in the Midwest (39th warmest), while precipitation was generally below normal (29th driest). The driest zone in the region stretched from southwestern Missouri, through Illinois and Indiana, to Lake Erie. In this area, precipitation totaled less than one inch for the month (Figure 1), which is less than 50% of normal (Figure 2). Only Wisconsin was considerably above normal in precipitation, with its 13th wettest February, while Missouri had its 14th driest February, Illinois its 11th driest, and Indiana its 10th driest. Much of the Wisconsin moisture was delivered in the form of snow, more than 25 inches in the northern part of the state (Figure 3a). A broad swath from Nebraska to northern Michigan received more than 10 inches of snow, which is at least 200% of normal snowfall (Figure 3b). It was several degrees warmer than normal in the northern Great Lakes region (Figure 4), and similarly cooler than normal in southwest portion of the Midwest. Air masses entering the region help to explain both the warmer temperatures and the heavy snow in the northern Midwest this February. The circulation pattern of a split flow (Figure 5a, Climate Diagnostic Center) occasionally allowed low pressure centers from the Southwest to move northeast over the Midwest and drag Gulf of Mexico air northward. At other times, clipper system came around the northwest ridge and moved into the northern Midwest. The result was a weaker trough than normal over the Great Lakes (Figure 5b, CDC), warmer air holding more moisture, and more snow in the northern Midwest. Eau Claire, WI, set a new February snowfall record of 24.3 inches, and it was the second snowiest February at Iron Mountain, MI, at 24.9 inches.