July 25-31, 2011
Midwest Weekly Highlights - July 25-31, 2011
Same Old Song
Hot, humid weather continued across most of the region the last week of July, although the heat was not as severe as it was the previous week. In addition, while most of the region received little rainfall, localized torrential thunderstorms caused serious flash flooding in Iowa and adjacent portions of Illinois.
Temperatures this week ranged from 5°F to 8°F across the southwestern half of the region, and 2°F to 5°F across the northeastern half (Figure 1). While daily maximum temperatures exhibited a similar range of departures, the largest factor in the much above normal warmth were the daily minimum temperatures. The high moisture content of the air prevented minimum temperatures from falling much past the low to mid 70s during the week. Average daily minimum temperatures this week ranged from 9°F above normal in northern Missouri eastward into western Illinois, to 3°F to 6°F above normal in eastern Kentucky (Figure 2). In the Arrowhead of Minnesota were frequently in the 50s, and average daily minimum temperatures ranged from 0°F to 2°F below normal. The band of high positive departures extended from the northern half of Missouri into southern Iowa, and eastward into western Illinois. There were 246 high daily minimum temperature records set this week, compared to only 70 record high maximum temperatures.
Flooding Causes Major Damage
Rainfall was more frequent in the northern Midwest, but over the remainder of the region scattered thunderstorms produced only localized and spotty rainfall (Figure 3). Scattered severe storms occurred during the week, including four reports of weak tornadoes in Iowa, Illinois, and Minnesota (Figure 4). For the second week in a row, torrential rainfall produced damaging flash flooding. East-central Iowa and adjacent portions of northwestern Illinois were the center of the bulls-eye this week. On July 27th a stationary weak frontal boundary extended from Minnesota southeast through eastern Iowa into central Illinois (Figure 5). An upper level disturbance approached from the west late in the day, and that combined with the warm, moisture-laden air riding north across the frontal boundary produced training thunderstorms. By the morning of July 28th seven to fifteen inches of rain had accumulated in extreme east-central Iowa and the northwestern corner of Illinois (Figure 6). The Dubuque, IA Airport (Dubuque County) recorded 10.31 inches of rain, and a station in Galena, IL(Jo Daviess County) recorded 13.45 inches of rain, both of these record breaking rainfalls. Flash flooding and river flooding was triggered by the rainfall. The flash flooding claimed one life in rural Galena when a man stranded in his vehicle was swept away by floodwaters. Emergency crews conducted more than 10 other water rescues. The flooding caused major damage in East Dubuque, IL (Jo Daviess County), turning the hilly streets into raging rivers, sweeping away numerous vehicles, uprooting trees, and filling basements with more than five feet of water.
The heavy thunderstorms erupted further east on July 27-29 as well, with three to more than seven inches of rain falling in Lower Michigan (Figure 7). Dimondale (Eaton County) recorded 7.15 inches of rain. Lansing, MI (Ingham County) was one of the harder hit areas, with homes washed off foundations and numerous roads closed.
MIssouri River Flooding
Minor to moderate flooding continued along the Missouri River across the state of Missouri. Major flooding was occurring in St, Joseph, MO (Atchison County) but the river was falling and was expected to fall through the first week of August.
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