August 22-31, 2008
Midwest Weekly Highlights - August 22-31, 2008
Dry Conditions Persist Despite Scattered Heavy Rain
Much of the Midwest continued to be very dry the last 10 days of August. The driest area extended from northwestern Wisconsin south-southeast through Indiana and into northern Kentucky, where rainfall was only 10 to 25 percent of normal (Figure 1). Rainfall was near to above normal in the mid-Mississippi River Valley, the Michigan Upper Peninsula, and from extreme southeastern Kentucky into southeastern Ohio. The rain in this area was largely due to the remnants of Tropical Storm Fay. There was an expansion of Moderate (D1) drought conditions in the Midwest depicted on the August 26 U.S. Drought Monitor (Figure 2). The Moderate drought expanded from Minnesota into Wisconsin, and Abnormally Dry (D0) conditions became more widespread in Minnesota, Wisconsin, and Ohio.
The weather was cooler than normal across the western two-thirds of the region this period, with temperature departures ranging from near normal in western Indiana to 3°F below normal in northern Missouri and much of Iowa (Figure 3). Temperatures in the Ohio Valley northward to southern Michigan ranged from 1°F to 3°F above normal.
Early Fall-like Conditions
High pressure dominated the Midwest the last ten days of the month as two cold fronts ushered cooler and drier air masses into the region. The first of the fronts entered Minnesota and Iowa on August 22 and was moisture-starved producing only widely scattered showers and thunderstorms (Figure 4). The weather the last 10 days of the month was characterized by seasonably warm days and pleasantly cool nights. The dry air allowed overnight temperatures to drop into the 50s and low 60s across all but far southern portions of the region. The coolest weather occurred on the morning of August 24, when minimum temperatures reached the 40s in northern Iowa and the first 32°F temperature since spring was observed in northern Minnesota (Figure 5). Marshalltown, IA reached a new record low temperature of 50°F on August 24, breaking the old record of 53°F set in 2005.
Fay Skirts Southern Midwest
The remnants of Tropical Storm Fay, which made landfall on the Gulf Coast for the last time on August 24, slowly moved into the southern Appalachians (Figure 6). On August 26-27 the moisture from Fay resulted in rain across the eastern half of Kentucky and southeastern Ohio, an area that has been experiencing an extended period of dry weather. Rainfall totaled 1 to 4 inches in eastern Kentucky and 1 to 3 inches in Ohio (Figure 7).
Severe Weather Hits Missouri
Back to the northwest, the second cold front of the period ignited thunderstorms from northwestern Wisconsin to western Iowa. The thunderstorms continued to fire along the front as it moved through Iowa and into Illinois on August 28. Severe weather moved through northern Missouri beginning late in the afternoon on August 28 (Figure 8) and there were numerous reports of severe weather from these storms in northern and central Missouri as well as some flash flooding. Twenty people were injured in Columbia, MO (Boone County) when thunderstorms winds caused a tent to collapse on people attending a church function. In Holliday, MO (Monroe County) an 80 mph wind gust was reported, and winds were sustained at 50 to 60 mph for approximately 10 minutes.
There were only a few other scattered reports of severe weather during the period in Iowa, Illinois, Michigan, Minnesota, Ohio, and Wisconsin.
As the month ended the Midwest was dominated by a large ridge of high pressure that extended from New England to Texas (Figure 9). Hurricane Gustav was churning in the Gulf of Mexico and taking aim on the central Gulf Coast.
SDH