September 22-30, 2023 Climate Summary

Above Normal Temperatures Region-Wide

September’s final days were quite a bit above normal in the temperature department. Iowa, Minnesota, and Missouri saw average temperatures 8-12°F above normal (Figure 1). Every state in the region saw average daily temperatures that were, to some degree, above normal.

While the average daily temperatures themselves were above normal, the average minimum temperatures were even more above normal for the period. Most of the Midwest saw minimum temperatures that were 5-10°F above normal, but Minnesota and Wisconsin had minimum temperatures that averaged 10-15°F above normal (Figure 2). In fact, over 200 daily temperature records were broken, with over 150 being record high minimums (Figure 3). Most of the record high minimums were in Minnesota and Wisconsin. Normal minimum temperatures in northern Minnesota are usually 35-45°F for September 22-30, but most towns in the region saw minimum temperatures in the 50s (Figure 4). Hibbing, Minnesota had a record high minimum of 60°F on September 23, which is 22°F above normal for that date. International Falls, Minnesota, right on the Canadian border, also set a record high minimum temperature of 60°F on September 23.

Average daily maximum temperatures were also above normal across the region. Much of Missouri, along with parts of Illinois and Iowa, saw maximum temperatures that were 8-12°F above normal (Figure 5). On September 29, Sioux City, Iowa, reached 95°F, which set a daily record. Des Moines, Iowa, also set a record that same day, with a maximum temperature of 91°F. On September 30, St. Joseph, Missouri set a record with a maximum temperature of 94°F, and so did Quincy Illinois, with a maximum temperature of 94°F.

Major Rain for Upper Midwest, Light Rain Elsewhere

Most of the region saw paltry rain totals, generally within the range of 0.05-0.5 inches (Figure 6). However, the Upper Midwest won the rain game this past week, with parts of Minnesota and Wisconsin coming in at 4-6 inches of rain. In the short period that was September 24-26, the Duluth area picked up over 6 inches of rain. Much of northwestern Wisconsin, including the town of Superior, received 3-4 inches of rain from the same event.

A low pressure system that passed through Minnesota on September 29 dropped healthy rain amounts through the morning of September 30. Parts of the Twins Cities saw over two inches of rain from this one event.

Drought Improves to the West, Expands to the East

While drought continued to expand through the Ohio Valley, hard-hit areas of the Upper Midwest finally caught a break with a fairly significant removal of extreme (D3) and exceptional (D4) drought (Figure 7). Almost all exceptional drought was removed in Iowa. This was in addition to a large chunk of D3 that was removed from Minnesota. While the Twin Cities continued to border on extreme drought, areas further up the Mississippi River saw significant improvement. At the beginning of September, Duluth, Minnesota was nearly in exceptional drought. Several bouts of heavy rain have brought the city closer to normal, with only abnormally dry conditions (D0) left in the Arrowhead region.

On the flip side, very little changed this past week for Missouri, most of Iowa, and Illinois. While some noteworthy rain events have affected the Chicago area, most of Illinois was still in abnormally dry conditions or moderate drought (D1). To the east, a major expansion of moderate drought continued through most of Indiana, and even into western and southern Ohio and Kentucky.

Many river gauges in the Midwest were still sitting at or below the low water threshold this past week. The Ohio River at Cairo, Illinois remained at or below the low water stage of 9.2 feet the entire week, rising slowly to 8.03 feet by the end of the month (Figure 8). The Wabash River at New Harmony, Indiana was sitting at 0.73 feet for much of the period, which is 3 feet below the low water stage (Figure 9). Even as far north as Minnesota, the Mississippi River at Highway 610 in Brooklyn Park hovered right near the low water stage until September 30, when the river rose ever so slightly from a low of 1.45 feet (Figure 10).

Storm Reports

After several weeks of little to no severe weather, over 150 storm reports came in during the final week of September. There were 70 reports of hail, 48 wind reports, and five tornado reports (Figure 11). A brief rain-wrapped tornado was spotted in an open field in Lac qui Prairie, Minnesota on September 23. The same storm system dropped quarter-size hail in Harrison and Carroll counties in Iowa, and created 60-70 mph straight-line wind gusts in Missouri. On September 25, an EF-U tornado briefly touched down in Dane County, Wisconsin in a corn field before quickly lifting.