Midwest Weekly Highlights - April 22-30, 2009

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Warmth Pushes Up from the South

Several days of warm southerly winds brought a big warming to the region. On average, cool temperatures occurred only in northwest Minnesota (2 to 4°F below normal) and near normal temperatures from Iowa to northern Michigan, however even those areas experienced a couple days 10 to 20°F above normal. Average temperatures ranged from 10°F above normal in northeast Ohio to 4°F below normal in northwest Minnesota (Figure 1). Temperature departures exceeded 6°F south of a line from the Ozarks in southwest Missouri to Lake Erie.

There were many records set with each day logging at least a few record values. Some record low temperatures on the first two days of the period gave way to hundreds of record highs across the region from April 23 to April 30. Numerous record high maximum temperatures were set, especially in the southern half of the region. Even more record high minimum temperatures were set as the strong southerly winds advected warm air and prevented nighttime inversions. Maximum temperatures hit 90°F in Missouri, Iowa, Minnesota, Wisconsin, and Kentucky. Other states in the region reached the upper 80s.
 

Heavy Rains Mitigate Drought

Heavy rains (200% of normal) fell across northern Missouri, Illinois, Iowa, Wisconsin, and Michigan (Figure 2). 52 stations (21 MO, 20 IA, 6 WI, 4 MI, and 1 IL) in the region received over 4.00" of rain. With the upper midwest receiving more than twice its normal precipitation, the severe drought area (Figure 3) was reduced considerably. Ohio and Kentucky were drier but received rain after the morning observations on April 30.
 

Wind, Hail, and Tornadoes

The frontal system that was responsible for much of the rain also brought severe weather to the region. On April 24, large hail fell from southwest Iowa to upper Michigan with reports of hail 2" or greater in Iowa (Floyd County) and Wisconsin (Trempealeau and Clark counties).

Two tornadoes were reported in Missouri (Clinton and Dekalb counties) on April 25. Also large hail (1" or greater) occurred in Missouri, Iowa, Illinois, and Michigan. Strong thunderstorm winds in southeast Michigan caused widespread damage to trees and power poles leaving more than a 125,000 Detroit area customers without power.

April 26 brought large hail and tornadoes to northeast Iowa (Linn and Delaware counties). Tornado winds damaged trees, homes, outbuildings, and destroyed camping trailers at the Flying Squirrel Campground. Other tornadoes were reported in Ringgold County, Iowa and Grant County Wisconsin.

On April 30, most of the severe weather was south of the region but a brief tornado touchdown was sighted in Graves County, Kentucky. The tornado was relatively weak and damage was limited.
 

Renewed Flooding Threat

The swath of heavy rain renewed flooding threats from northern Missouri to Michigan. Small rivers and streams rose quickly with the additional rains (Figure 4). The deluge left standing water in fields that had begun to dry during the warm and windy weather that preceded the rain.
 

MST