September 2010
Midwest Overview - September 2010
Wet and Cool Northwest, Warm and Dry Southeast
September weather in the Midwest was characterized by sharply different regimes in the northwest half and southeast half. The northwestern half of the region experienced and active weather pattern, with near to below normal temperatures and rainfall that was generally well above normal. The weather was more persistently warm and dry in the southeastern half of the region. Overall, weather in the southeastern half of the region was very favorable for field work and corn and soybean harvest continued to run well ahead of the five-year average. Despite wet weather, corn and soybean harvest in Iowa and Wisconsin was slightly ahead of the five-year average. Harvest in Missouri was ahead of average, but varied greatly by region. Corn harvest was complete in the Bootheel at the end of the month, while wet weather delayed harvest in the western portions of the state. Minnesota corn and soybean harvest was running slightly behind average.
September Temperatures
Temperatures across Minnesota,Wisconsin, and the Michigan Upper Peninsula were 1°F to 3°F below normal during the month (Figure 1). Cold fronts frequently moved south through these states, then typically stalled out over the central Midwest. In the central third of the region, September temperatures were near normal, although they were highly variable during the month. In the southeastern third of the region, temperatures were 1°F to 3°F above normal, with the greatest departures in the Ohio Valley.
The month started out much cooler than normal, with temperatures running from 1°F to 7°F below normal across the region the first ten days of September (Figure 2). During the middle third of the month it remained cool in the northern Midwest, while temperatures ran from 1°F to 4°F above normal in the south (Figure 3). The last ten days of September were warmer than normal everywhere but the far north, with departures running 6°F above normal in the Ohio Valley (Figure 4). More than 270 record maximum and record high minimum temperatures were set in this period, including two readings of 100°F in Kentucky.
Too Much Rain on One Hand, Not Enough on the Other
The active weather pattern across the central and northern Midwest brought abundant rainfall to those areas, while in the southwestern half of the Midwest lack of rain exacerbated the developing drought conditions. Monthly rainfall across most of Minnesota, Wisconsin, Iowa, and Missouri was at least twice normal, with an area of 300 percent of normal across southern Minnesota (Figure 5). A preliminary analysis of Minnesota's rainfall by the Minnesota State Climate Office indicates that September 2010 was the wettest September in Minnesota's modern climate record. The state-average September rainfall total was 6.46 inches, topping the previous high of 6.20 inches from 1900. Rainfall was above normal over all but small portions of north-central and northeast Iowa (the same areas that were relatively dry during August). Monthly rain totals varied from 2.48 inches at Charles City (Floyd County) to 16.05 inches at Allerton (Wayne County). Allerton’s hefty total was still shy of a September record at that location (18.57 inches in 1926) but pushed their annual total past 60 inches. Iowa’s statewide average precipitation for the year to date already ranks as the ninth highest among 138 years of records with three months to go.
In Missouri preliminary rainfall data indicate a statewide average of 8.46 inches, nearly four inches above normal for the monthly. It was the fifth wettest September on record and the wettest September since 1993. All areas of the state experienced above normal rainfall with the exception of the Bootheel. Excluding the northwestern tip, the western one third of Missouri reported highest monthly totals between 8 to 12 inches, whereas the Bootheel averaged less than three inches. A few counties in southwestern Missouri reported more than 14 inches of rain for the month with a couple communities in Christian and Greene counties reporting nearly 19 inches. Alternatively, two Bootheel locations, Kennett (Dunklin County) and Caruthersville (Pemiscot County), reported less than one inch for the entire month, and the Bootheel is classified as in Severe Drought on the U.S. Drought Monitor. At the end of the month Severe Drought was also depicted over much of southeastern Indiana.
Heavy Rain Results in Fall Flooding
A major rain storm on September 22-24, on top of an already wet month, pushed many rivers well over flood stage in Minnesota and Wisconsin. Six to ten inches of rain fell in the southern tier of Minnesota counties, with a number of locations setting new monthly and all-time daily rainfall records. The flooding closed roads and resulted in evacuations in some areas. At the end of the month moderate flooding was observed on the Minnesota, Wisconsin, and Mississippi Rivers, and in general streamflows were well above normal across the northern Midwest (Figure 6).
Severe Weather Makes a Mark
Severe weather occurred at some point in all states except for Indiana during the first three weeks of September (Figure 7). The most notable severe weather hit during the third week of September. A tornado outbreak occurred in Ohio on September 16, when at least seven tornadoes were confirmed. A hailstone 5.5 inches in diameter was reported in western Missouri on September 18 and hail two inches or more in diameter caused extensive damage to vehicles during that event. There was no severe weather reported in the Midwest from September 23 to September 30.
-SDH-
The Minnesota State Climate Office, the Iowa State Climate Office, and the Missouri State Climate Office also contributed to this report.