Midwest Overview - September 2011

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An Interesting Month

September 2011 started off where summer left off - hot. A heat wave the first three days of the month set record maximum temperatures across the region, with a number of locations reaching maximums in excess of 100°F. Temperatures the first three days of September were well above normal across the entire Midwest, with departures from 9°F to 14°F above normal from Missouri east-northeast to Ohio (Figure 1). However, that was the last of the unseasonably warm weather for most of the region. Temperatures the remainder of September were 4°F to 5°F below normal across the central Midwest, dropping to near normal on the periphery of the region from northern Minnesota around to eastern Ohio (Figure 2). This same pattern was reflected at the end of the month, with average daily temperatures for September ranging from 2°F to 4°F below normal in the central Midwest, and near normal across most of Minnesota, northern Wisconsin, Michigan, and Ohio (Figure 3).

For most of September it was dry across the Midwest, with the exception of along and south of the Ohio River (Figure 4). That changed the last ten days of the month, when an upper level low stalled over the southern Great Lakes and brought frequent and sometimes heavy rain to the eastern half of the region (Figure 5). Precipitation the last ten days of the month was 200 to more than 400 percent of normal from Wisconsin and Illinois eastward (Figure 6). West of the Mississippi River, however, rainfall was well below normal and existing areas of drought saw little relief. For the entire month, precipitation was normal to 300 percent of normal from eastern Wisconsin and Illinois east through Ohio and Kentucky (Figure 7). Most of Minnesota, Iowa, and northern Missouri received less than 50 percent of normal precipitation.
 

Waterspouts and Winds

Smoke from a wildfire in northern Minnesota was transported south into Wisconsin, Illinois, and Indiana on September 13th by strong northwest surface winds. The smoke reduced visibility in northern Illinois and was easily detected as far south as central Illinois and Indiana. The upper level low over the central U.S. at the end of the month generated some unusual weather. On September 24th there were numerous reports of waterspouts over Lake Michigan from Milwaukee south to Chicago. Thunderstorms produced a few weak tornadoes in Indiana, Kentucky, and Michigan during the week. On September 29th, a strong cold front swept through the Midwest and was followed by very windy, cool weather. Winds gusted to between 50 and 60 mph across the northern half of the region, and there were numerous power outages and reports tree damage from the winds. A wind gust of 68 mph was reported at a crib in southern Lake Michigan. The strong north-northwest winds combined with a 200 mile fetch over the lake to generate waves to 25 feet over southern Lake Michigan (Figure 8). In northwestern Iowa, firefighters had difficulty responding to the many field fires resulting from very dry conditions and the strong winds.

At the end of September freezing temperatures had generally been recorded as far south as central Iowa, Wisconsin, and the northern half of Lower Michigan. There were scattered occurrences south through central Illinois, and through Indiana to the Ohio River. A hard freeze (28°F) had occurred in northeastern Minnesota, northern Wisconsin, and northern Lower Michigan.

For more details on weather and climate events during September 2011, click on the individual weekly report links on the upper right.

The Iowa State Climate Office and Indiana State Climate Office also contributed to this report.

-SDH-