Temperature

Average temperatures for the week hovered near normal for much of the region (Figure 1). Sothern extremities were just above normal by 3-5°F, while parts of the Upper Midwest were below normal by a similar 3-5°F range. Southern Missouri and Kentucky benefited from high pressure over the southeast which kept temperatures mild, while multiple cold fronts moved in from the upper Midwest starting December 9.

Anomaly patterns were similar for minimum temperatures, which averaged just below normal to the north and just above normal to the south (Figure 2). Temperatures were especially below normal for much of the region after a strong cold front came through on December 11. By December 12, many locations struggled to see temperatures above the single-digits and teens. In Maple City, Michigan, a station observed a minimum temperature of 5°F on December 14, which was the earliest temperature less than or equal to 5°F in December since 2013. Lake Geneva, Wisconsin observed three consecutive days of minimum temperatures at or below 0°F from December 12-14, the earliest occurrence in December since 1995. In Duluth, Minnesota, wind chills reached -40°F on December 12, the earliest occurrence in meteorological winter since December 1995.

Maximum temperatures were slightly above normal south of I-80, near normal for most of Michigan, Wisconsin, Iowa, and northern Illinois, and below normal in northern Wisconsin and Minnesota (Figure 3). The week started off with record-breaking warmth, as temperatures reached the mid-60s in parts of Iowa. In Sioux City, Iowa, the temperature was greater than or equal to 65°F for two consecutive days, December 7-8, for the first time in December since records began in 1889. In Couderay, Wisconsin, a station with records dating back to 1948 observed a maximum temperature of -1°F, the coldest maximum temperature in the first two weeks of December since 2013.

Precipitation/Snow/Drought

Most of the region saw below-normal precipitation, especially much of Minnesota and Wisconsin which observed less than 20 percent of normal precipitation (Figure 4). In northern Minnesota, precipitation was well above normal compared to the rest of the region, coming in at over 200 percent of normal. Much of what did fall fell as snow, with nearly a foot in much of the far northern reaches of the region. Roads in Michigan’s UP were closed due to blowing snow and whiteout conditions on December 11. The same frontal system brought snow showers and squalls to Illinois and Indiana December 11-12, with squalls on the 12th creating hazardous driving conditions stretching from Lafayette to Muncie.

By December 10, drought was creeping back into the picture. Parts of Indiana and Illinois saw expansions in D1 (moderate drought) and D2 (severe drought) (Figure 5). Drought was unchanged for most of the rest of the region.