September 2023 Overview – Midwestern Regional Climate Center

Temperature

The average September temperature for the Midwest was 66.2°F, which was 2.6°F above the 1991-2020 normal. Temperatures ranged from near normal in the east to up to 5°F above normal in the west (Figure 1). Statewide average temperatures ranged from 0.7°F above normal in Kentucky to 5.0°F above normal in Minnesota (Figure 2). Rankings indicate Minnesota had the 2nd warmest September on record and Wisconsin had the 6th warmest. Minneapolis, Minnesota had its warmest September in 151 years. Duluth, Minnesota had its 3rd warmest September in 150 years. Duluth also recorded its first-ever temperature at or above 95°F in September, with a temperature of 97°F on September 3. With 28 days, St. Louis, Missouri tied the record for the greatest number of days in September with maximum temperatures at or above 80°F, dating back 148 years. September started with record warmth regionwide, with notable warmth in the northwestern portion of the region. Three-day average high temperatures from September 2-4 ranged from 95-100°F for many locations in Iowa, Minnesota, and Wisconsin (Figure 3). Conditions flipped briefly in mid-September, with below-normal temperatures blanketing the Midwest. On September 13 and 14, the region’s first frost advisories for the season were issued across northern Wisconsin and northern Michigan, and temperatures across upper Minnesota dipped below freezing. The month ended with unseasonable warmth as temperatures soared over 90°F. Across the region, temperatures averaged 2-12°F above normal during the last week of September (Figure 4).

Precipitation

September precipitation totaled 2.21 inches for the Midwest, which was 1.21 inches below normal, or 65 percent of normal. While most of the region had precipitation that was 10-75 percent of normal, precipitation was 75-200 percent of normal from northern Illinois northward into Wisconsin and eastern Minnesota (Figure 5). Statewide precipitation totals ranged from 2.33 inches below normal in Ohio to 0.05 inches above normal in Minnesota (Figure 2). Rankings indicate Ohio had its 5th driest September since 1895. Youngstown, Ohio had its 2nd driest September in 96 years. Sault Ste Marie, Michigan had its 3rd driest September in 136 years. Green Bay, Wisconsin had its 4th driest September in 138 years. Conversely, Duluth, Minnesota had its 2nd wettest September in 150 years, with 10.36 inches of rainfall. The greater Duluth area recorded multiple extreme rain events throughout the month, including nearly 4 inches on the 6th, over 3 inches on the 12th, and over 5 inches from the 24th to the 25th. The Chicago area was hit hard by heavy rains on September 17, with an isolated pocket of 3-6 inches resulting in destructive flash flooding across the south suburbs.

Drought

Abnormal dryness and drought expanded across the Midwest during September, affecting portions of all nine Midwestern states. The month concluded with about 83 percent of the region dry or in drought, up about 18 percent compared to the start of September (Figure 6). The most severe and widespread drought persisted in the northwest, although normal to above-normal precipitation slightly improved conditions in Minnesota and Wisconsin. Iowa exceeded 170 consecutive weeks of at least moderate drought, the longest drought for the state in the U.S. Drought Monitor’s nearly 24-year period of record. In the east, moderate drought expanded into Indiana, Kentucky, and Ohio as precipitation deficits grew throughout the month.