September 2024 Overview – Midwestern Regional Climate Center

Temperature

The average September temperature for the Midwest was 67.1°F, which was 3.5°F above the 1991-2020 normal. Temperatures were above normal regionwide, with the warmest anomalies across the upper Midwest and temperatures just slightly above normal in the far southern Midwest (Figure 1). Statewide average temperatures ranged from 1.6deg;F above normal in Missouri to 6.6°F above normal in Minnesota (Figure 2). Final rankings indicate that Minnesota had its warmest September on record. Numerous long-running observation sites across Minnesota also reported their warmest September on record, with records broken in Minneapolis, St. Cloud, and Duluth. Sault Ste Marie, Michigan, had its warmest September, dating back 137 years. The first week of September was marked with temperatures 1-7°F below normal regionwide (Figure 3). La Crosse, Wisconsin, had its earliest 40°F reading in September since 1986. Temperatures quickly rebounded by mid-month, with persistent warmth lasting through late September. Vast swaths of Wisconsin and Michigan had a record consecutive streak of daily high temperatures at or above 80°F for September (Figure 4).

Precipitation

September precipitation totaled 2.12 inches for the Midwest, which was 1.3 inches below normal, or 62 percent of normal. There was a decisive north-south gradient in rainfall, with extreme dryness to the north and extreme wetness to the south (Figure 5). Statewide precipitation totals ranged from 2.76 inches below normal in Iowa to 2.7 inches above normal in Kentucky (Figure 2). Final rankings indicate Kentucky had its 5th wettest September on record. The remnants of Hurricane Helene largely drove Kentucky’s anomalous wetness. Helene brought 4-6 inches of widespread rain from September 27-29 (Figure 6). Before Helene, accumulated monthly rainfall was just 25-75 percent of normal across central and eastern Kentucky. Conversely, final rankings indicate that Iowa and Minnesota had their 1st driest September on record, and Michigan had their 3rd driest September on record. Cedar Rapids, Iowa, and Minneapolis, Minnesota, had their driest September on record. Numerous other long-running stations across Iowa, Minnesota, and Michigan had a top five driest month (Figure 7).

Drought

The month ended with about 78 percent of the Midwest classified as abnormally dry or in drought, according to the U.S. Drought (USDM) map (Figure 8), which was about a 34 percent expansion compared to the start of September (Figure 9). Exceptional (D4) drought remained widespread across southeast Ohio, while moderate to severe drought was introduced across the far upper Midwest. Abnormally dry conditions blanketed most of the region. The only areas to see significant improvement in dryness were southeast Missouri, southern Illinois, and Kentucky.