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Midwest Weekly Highlights - December 25-31, 2017

Arctic Chill

Record cold temperatures were widespread across the Midwest during the final week of December (Figure 1).  The entire region was 10°F or more below normal, with areas in northern Minnesota and northern Wisconsin more than 25°F below normal.  Minimum temperatures averaged below-zero across Iowa, Minnesota, Wisconsin, northern Illinois, and most of Michigan (Figure 2).  Wind chill advisories and warnings were in effect across most of the region during the period as wind chill values in the -20°F to -40°F range were widespread.  Two of the coldest mornings were December 27 (Figure 3) and December 28 (Figure 4), where minimum temperatures of -10°F to -20°F were common across Iowa, Wisconsin, Minnesota and the U.P. of Michigan.  The coldest observations during the period were in St. Louis County, MN, with -40°F in Kabetogama and -42°F in Cotton through the morning of December 28, and -45°F in Embarrass through the morning of December 31. New Year’s Eve was also very cold across the region, where temperatures on the morning of January 1 were only above zero in Kentucky, southern Missouri and western Lower Michigan (Figure 5).

More than 1,100 daily low maximum and minimum temperature records were broken during the bitterly cold period (Figure 6).  While several hundred records were for minimum temperature, more than 800 were for low maximum temperatures.  More than 500 daily low maximum temperatures were broken through the mornings of January 27 (Figure 7) and January 28 (Figure 8) combined.   Nearly 200 more daily records were broken through the morning of January 1, as well.

Snowy for the Central Midwest, Western Michigan

Moderate snowfall fell across the central Midwest, with 4-6 inches in some locations (Figure 9).  More than 10 inches of lake-effect snow fell along the western shores of Lower Michigan.  Most of these areas received more than twice the normal amount (Figure 10).  Lesser amounts of snowfall—up to two inches—also fell in northern Minnesota, Wisconsin, northern Missouri, southern Illinois, southern Indiana and eastern Kentucky.  However, the snowfall did not translate to a large amount of liquid precipitation (Figure 11).  Only a few areas in northwestern Iowa and western Lower Michigan had above-normal precipitation for the period (Figure 12).