Midwest Weekly Highlights - August 15-21, 2006

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A Quiet Week

Much of the Midwest experienced near normal to cooler than normal weather this week. The exception was southwestern Missouri, where the cool air was not able to displace the heat for any length of time.  Temperatures this week were 2°F to 4°F across southwestern Missouri, but more than 2°F below normal from northern Missouri through central Iowa (Figure 1). Rainfall during the week was again concentrated in a band that marked the general southern extent of the push of the cold fronts (Figure 2). Rainfall was more than two times normal in southern Iowa, northern Missouri, parts of southern Illinois, Indiana, and western Kentucky. It remained dry from central Michigan westward across Wisconsin and into central Minnesota. The August 15 edition of the U.S. Drought Monitor intensified the drought in western Missouri to the Extreme category (Figure 3). Most of the rain this week was limited to northern Missouri and missed the heart of the drought area. Rainfall for the month through August 21 (Figure 4) is less than 75 percent of normal in much of southwestern Missouri, and less than 50 percent of normal from southern Wisconsin through central Michigan and across much of northern Ohio.


Relief Arrives 

The week began with cooler and and much less humid air spreading through the region, bringing a much welcomed break from the heat and humidity to the southern portions of the region. On the morning of August 15 minimum  temperatures were in the upper 30s in northern Minnesota and in the 50s as far south as central Missouri (Figure 5).  Afternoon temperatures in Missouri generally reached only the upper 80s to around 90°F, but the air was very dry with dewpoints in the upper 40s and 50s (Figure 6).


Hit and Run Heat in Missouri

The break from the heat in Missouri was short-lived, and by August 17 triple-digit readings were back in southwestern Missouri as the high pressure system that brought the cooler, drier air retreated to the east. Joplin, MO reached 102°F on August 17, and Springfield hit 101°F on August 18, while many other locations were in the upper 90s. However, another cold front was poised to the west and kept the return of the heat brief. This system moved through Missouri on August 18-19 and was followed by a large high pressure system that settled in over the entire Midwest the remainder of the period (Figure 7).

In response to the intensifying drought and continuing hot and dry weather in Missouri, the Missouri Drought Assessment Committee on August 16 declared Phase 3 Drought (conservation phase) for 37 Missouri counties, an increase of 16 counties since late July. A Phase 2 drought (alert phase is in effect for 44 counties, and a Phase 1 drought (advisory phase) is in effect for the remainder of the state. .


Spotty Severe Weather

The passage of cold fronts helped trigger scattered severe weather in parts of the Midwest during the period. Severe thunderstorms occurred in Minnesota, Missouri, Illinois, and Kentucky. On August 16 a tornado rated as F0 touched down near Ross, MN (Roseau County) causing minor damage along an intermittent three-mile track.

SDH