Monthly Overview - December 2020

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Mostly Dry December

Precipitation was limited across the Midwest in December (Figure 1). Regionwide, 1.42 inches fell, which was 0.79 inches below normal. The lack of precipitation ranked as the 25th driest on record for the region (1895-2020). Large areas of central Missouri, central Illinois, central Wisconsin, northern Iowa and southern Minnesota had less than half the normal amount of precipitation (Figure 2). Areas in southern Iowa, central Lower Michigan and eastern Kentucky had slightly above normal precipitation. Only a few areas in northern Minnesota were moderately above normal. Most of the precipitation fell during the final ten days of the week (Figure 3), as two major winter storms traversed the region.
 

Fairly Warm

Temperatures were warmer than normal in December in the Midwest (Figure 4). Region-wide temperature was 30.2°F, which was 4.2°F above normal. This ranked among the 20 warmest Decembers on record for the region (1895-2020). This warmth was more prevalent in the Upper Midwest, with areas in Minnesota significantly above normal. Maximum temperatures also were warmer than average temperatures (Figure 5), with more than 375 daily high maximum temperature records broken across the Midwest during the month (Figure 6). Fewer than 35 daily high minimum records were broken by contrast. Most of these records came during warm days on December 10 (Figure 7) and December 11 (Figure 8). While daily records were broken, monthly temperature records were not broken across the Midwest at any locations.
 

Snow Storms

Snowstorms impacted the Midwest on several occasions through December (Figure 9). The first of these storms traversed the Upper Midwest on December 11-14 (Figure 10), bringing moderate to heavy snow to Iowa, southern Wisconsin and Michigan. Most of the snow fell through the morning of December 12 (Figure 11), with lingering snow and lake-effect snow until the morning of December 14. Amounts of 6-10 inches were reported, with isolated higher amounts. Two more major winter storms brought heavy snow to the northern half of the Midwest during the holiday season. The first of these storms brought heavy snow to Minnesota, northwestern Iowa, northwestern Wisconsin and the Great Lakes from December 23-25 (Figure 12). Moderate snow fell through the morning of December 28 before the second major storm impacted the entire northern half of the Midwest on December 29-30 (Figure 13). Heavier bands of snow were recorded in east-central Iowa through northern Illinois. Lesser amounts of lake-effect snow were reported through December 31 as the storm dissipated. These two storms brought a total of more than 12 inches of snow to central Minnesota, east-central Iowa, and northwestern Illinois. Lake-effect snow in Michigan was even higher, with a report of 31.9 inches in the U.P. of Michigan. In total, more than 200 daily snowfall records were broken across the Midwest in December (Figure 14).
 

Drought Holds Serve

Despite drier conditions across most of the Midwest in December, low water demand kept drought from expanding significantly (Figure 15). Drought coverage increased by three percent during the month, with areas in northern Missouri and central Illinois seeing increases. Abnormally dry conditions expanded across most of Minnesota during the month, however, with abnormally dry conditions also introduced to southern Kentucky. In total, slightly more than 12 percent of the region was in drought as of the December 29 U.S. Drought Monitor.
 

2020 Annaul Summary

After two consecutive records for annual precipitation were broken in 2018 and 2019, values were near normal in 2020 across the Midwest (Figure 16). Annual precipitation for the region was 37.73 inches, which was 0.78 inches above normal. This was only two percent above the normal (Figure 17). Heavy rain was limited in the region, with scattered thunderstorms leading to above-normal precipitation in July (Figure 18) and May (Figure 19). One outlier state in 2020 was Iowa, which had only 82 percent of normal (Figure 20).

Temperature in the region warmer than normal (Figure 21). Regionwide temperature averaged 49.9°F which was 1.2°F above normal. A very warm July and March across the Midwest buoyed temperatures for the year, while unseasonably cold temperatures in April, May and October averaged annual temperatures to 12th warmest on record (1895-2020), well below the 2012 record.

Significant severe weather events led to multiple billion-dollar disasters in the region in 2020 (Figure 22). The most prominent of these was the August 10 Derecho that tracked through Iowa and northern Illinois. Millions of acres of corn and soybeans were flatted by the storm, as wind gusts over 100 mph were recorded. Hundreds of thousands of people were without power, with many still without power a week later. Other billion-dollar disasters in the region included severe weather across the Ohio River Valley on March 27-28 and a severe hail outbreak on April 7-8. Other impacts in the region included a dam breach near Midland, MI due to heavy precipitation from May 17-19. An evacuation prevented loss of life as 11,000 residents were moved to safety. The remnants of Tropical Storm Cristobal tracked through the Midwest and through Iowa for only the second time on record on August 8-10. The storm was only the third to track through on-shore Wisconsin as well. After 29 consecutive weeks without drought in the Midwest through the May 26 U.S. Drought Monitor, drought was observed for the first time on June 2. Drought impacted western Iowa from summer through the end of December with a lack of precipitation a contributing factor. Flooding, meanwhile, was limited, with areas in eastern Kentucky strongly impacted in February along with minor flooding throughout the spring in the Ohio River Valley and along the Mississippi River.
 

-BJP-