3rd Warmest December on Record since 1895 for Midwest

December average temperature for the Midwest was 33.9°F, which was 6.2°F above the 1991-2020 normal. The warmth was widespread, with temperature anomalies increasing from north to south across the region. Average temperatures were above normal in all nine states, with statewide averages ranging from 1.7°F above normal in Minnesota to a record-setting 9.8°F above normal in Missouri (Figure 1). Maximum temperatures were 1-14°F above normal across the region during December (Figure 2). There were 1015 daily maximum temperature records broken, with about half of those records set on December 15th and 16th (Figure 3). Missouri (282), Iowa (151), Illinois (142), and Wisconsin (111) reported the most daily maximum temperature records during the month. Several stations in Iowa broke the state’s December high temperature record of 74°F on December 15th – 16th (Figure 4). Minimum temperatures were 1-11°F above normal across the region, except across northern Minnesota where minimum temperatures were up to 3°F below normal (Figure 5). There were 440 warm daily minimum temperature records broken, with 104 records in Missouri alone (Figure 3).  

Variable Precipitation across the Midwest

Average total precipitation was 2.45 inches for the Midwest during December, which was 0.26 inches above normal. Precipitation was variable across the region with statewide average totals ranging from 0.55 inches below normal in Iowa to 0.95 inches above normal in Minnesota. Isolated locations in Minnesota received over 3.52 inches, which was 2.48 inches above normal. Additional locations in Indiana received over 5 inches of precipitation, which was 2.57 inches above normal for the month (Figure 6). The largest precipitation deficits were in western Iowa and northern Missouri where the monthly precipitation was 10-50 percent of normal (Figure 7). There were 342 daily precipitation records set during the month, with 127 records set across the region on December 11 (Figure 8).  

Snowfall across Northern Parts of Midwest

The most abundant precipitation fell across Minnesota, mostly as snow, where December precipitation was 200-400 percent of normal (Figure 9). Snowfall was above normal across northern Minnesota and northern Wisconsin where snow accumulations reached 20-40 inches during December (Figure 10). There were 164 daily snowfall records set in December, with most occurring in Minnesota (66) and Wisconsin (64) (Figure 11). Heavy snow fell across southeast Minnesota on December 10th-11th, with some locations accumulating 21 inches and snowfall rates approaching 2 inches per hour. However, for much of the Midwest, snowfall deficits were widespread, including a lack of lake effect snow (Figure 12). In western Michigan and northern Indiana, snowfall was 5-15 inches below normal. Snowfall across northeast Ohio was 10-25 inches below normal. Warm temperatures delayed the measurable snowfall across the lower Midwest. Chicago set a record for the latest first measurable snowfall on December 28, breaking the previous record by eight days (records dating back to 1884).  

Slight Improvement to Drought Conditions

Drought conditions improved slightly in the Midwest during December, although patchy drought and dryness lingered across the northern and western states (Figure 13). The most noteworthy changes happened across northern Minnesota where D3 (extreme drought) was eliminated from the U.S. Drought Monitor and D2 (severe drought) improved 17 percent. Drought intensified in southern Wisconsin, and abnormal dryness expanded throughout western Missouri. The eastern portion of the region remained drought-free. 

Complex and Severe Storm System December 10th-11th

A strong low-pressure system moved through the Midwest on December 10th-11th resulting in a widespread severe weather outbreak across Illinois, Indiana, Kentucky, Missouri, and Ohio (Figure 14). This storm resulted in 61 confirmed tornadoes and 234 high wind reports across the Midwest, with 81 fatalities and over 100 injuries in the region. The communities of Mayfield, Kentucky and Dawson Springs, Kentucky saw extensive damage after taking a direct hit from a long-track EF-4 storm. The historic “Mayfield tornado,” as its commonly called, was on the ground for 165.7 miles, had peak winds of 190 mph, and resulted in 55+ fatalities. Media reports indicated over 1,000 homes and businesses were destroyed in Mayfield. An EF3 tornado with peak winds of 150 mph struck Edwardsville, Illinois causing extensive damage to an Amazon facility and killing six people. In Kentucky, two mesonet stations are being investigated for having potentially measured a record setting wind gust on December 10th (Graves County, 107.1 mph; Caldwell County, 120.1 mph). The economic impact of this storm, including affected areas outside of the 9-state Midwest region, was given an initial estimated cost of $4 billion.  

Severe Weather Outbreak December 15th

A second historic severe weather outbreak on December 15th resulted in a derecho that spawned tornadoes and destructive thunderstorms in Iowa, Illinois, Minnesota, Missouri, and Wisconsin (Figure 15). This was the first known derecho in December anywhere in the United States, according to the National Weather Service (NWS). This unseasonable storm system resulted in the Storm Prediction Center issuing their first-ever Moderate Risk area in the Iowa/Minnesota/Wisconsin region during the month of December (dating back to 1990) and their first-ever December tornado watch in Minnesota. As of December 23rd, the confirmed tornado count in Iowa reached 63, which set a new daily record for tornadoes for Iowa. Seventeen tornadoes were rated EF2. Prior to the December 15th outbreak, there had only been five tornadoes reported since 1950 in Iowa during December. As of December 29th, the NWS confirmed 20 tornadoes in Minnesota, marking the first December tornadoes on record for the state. As of December 27th, eight tornadoes had been confirmed by the NWS in Wisconsin. One fatality was reported in Minnesota after a falling tree struck a man in Rochester. One fatality was reported in eastern Iowa after high winds caused a semi-truck to roll.