Midwest Weekly Highlights - September 22-30, 2010

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Warmth Lingers

The last nine days of the month were generally warm across the Midwest, with just the northern portions of the region near to below normal. Average daily temperature departures for the period ranged from 1°F below normal in northern Wisconsin to 5°F above normal in the Ohio Valley (Figure 1). The western half of the region was generally 1°F to 2°F above normal. Hot weather dominated the first half of the period, with more seasonable temperatures the last several days of the month. 272 record high temperatures and 86 record high minimum temperatures set during the first four days of the period, including a high temp record of 100°F at Barren River Lake, KY (Barren County) on September 22 and Rough River Lake, KY (Grayson County) on September 24.

Rainfall was much above normal across the northwestern half of the region, and normal to much below normal across the southeastern half (Figure 2). Rainfall was more than seven times normal for the period across southern Minnesota. Little to no rain fell in the Ohio Valley, and drought conditions persist from the Missouri boot heel to southwestern Ohio (Figure 3).
 

Heavy Rain Soaks Minnesota and Wisconsin, Causes Major Flooding

A strong low pressure wave developing along a front stalled out over the upper Midwest On September 22-23 produced extremely heavy rain in a wide band across the southern quarter of Minnesota into central Wisconsin (Figure 4). Three to six inches of rain in 24 hours was common in much of this area, with a band of six to ten inches of rain in the southern tier of counties in Minnesota (Figure 5). Some of the rain amounts reported in Minnesota were 10.53 inches in Amboy, MN (Blue Earth County) 9.82 inches near South Branch, MN and 8.75 inches in St. James, MN (Watonwan County), and 8.35 inches in Minnesota Lake (Faribault County). On September 23 six locations in Minnesota set all-time daily precipitation records, and 28 locations in Iowa, Minnesota, and Wisconsin set new monthly precipitation records.

Flooding across southern Minnesota was extensive. Numerous roads and highways in southern Minnesota were closed by the Minnesota Department of Transportation, and many were expected to remain closed for at least a week or more. Residents were preparing for flooding along the Minnesota and Mississippi Rivers. On September 26 Minnesota Governor Tim Pawlenty said he would call a one-day special legislative session in early October to provided assistance to southern Minnesota residents affected by the flooding. He had already submitted a federal disaster declaration request.

The Wisconsin River reached flood stage in Adams and Columbia Counties and levels exceed those reached in 2008. In Portage, WI (Columbia County), a 120 year-old sand levee began failing on September 26 and authorities began evacuating residents. Although leaking, the levee held and the river level was dropping by the morning of September 29.

 
High Winds Cause Damage

A strong low pressure system spinning over the Great Lakes (Figure 6) generated strong winds, gusting in excess of 45 mph, across Wisconsin, Michigan, and Ohio that resulted in power outages and damage on September 24-25. In Detroit, MI extra fire companies were called out to control fires that had ignited and were being fanned by the high winds. A Detroit man was killed when he was struck by a tree limb outside his home. A large oak tree blew over in Vermilion, OH (Erie and Lorain County) crushing a house.

-SDH-