December 2018
Monthly Overview - December 2018
Warm Temperatures
Despite getting off to a cold start, the monthly averaged temperatures across the state were above normal. Around the 12th of December, temperatures warmed to well above normal and then remained warm throughout the month. The warmest temperatures, compared to normal, where in the northwestern quarter of the region with values 4°F to 7°F above normal across much of Minnesota, Wisconsin, Iowa, and northern Illinois
(Figure 1). Nearly 300 daily record high temperatures (Figure 2) were set in December with most being record high minimum temperatures. Many of the record highs came in the middle of the month and were spread across all nine Midwest states. Fewer than 10 daily record lows
(Figure 3) were set in December across the Midwest.
Mixed Precipitation
Precipitation in the Midwest for December ranged from less than 75% of normal downwind of the Great Lakes to more than 200% of normal in western Iowa (Figure 4). Away from the Great Lakes, most areas had above normal totals especially in the south and west edges of the region. With warm temperatures, snowfall was below normal for nearly all of the Midwest
(Figure 5). Only Minnesota had large areas with above normal snowfall in December. Snowfall deficits of more than a foot, and more than 2 feet in some locations, downwind of the Great Lakes were due to the lack of lake-effect snows that typically fall in these areas. The snow that did fall in the Midwest was primarily from storms that book ended the month. On the 1st and 2nd, a storm tracked from Iowa to Upper Michigan and then during the last week of December, heavy snows fell across Minnesota.
Tornado Outbreak in Illinois on December 1st
An outbreak of tornadoes on December 1st struck Illinois (Figure 6). There were 28 confirmed tornadoes in the state. Although there were no fatalities, the EF-3 tornado that struck Taylorville, Illinois
(Christian County) caused 22 of the reported 23 injuries in the state as well as damaging more than 500 homes. Also on the 1st, a couple dozen large hail reports came from Illinois and Ohio and a handful of damaging wind reports from Illinois. Tornadoes were also reported on the 31st in Indiana and Kentucky
(Figure 7). Kentucky had more than a dozen reports of damaging thunderstorm winds on the 31st while a handful of such reports also came in from Illinois and Indiana. The only other severe weather reports in December came from Ohio on the 2nd (Figure 8) and Missouri on the 4th
(Figure 9).
Drought Sparse
The month both began and ended with no drought in the region. Some drought emerged in Missouri during the month but was removed by the US Drought Monitor valid on January 1st (Figure 10). As of January 1st, the percentage of the Midwest classified as abnormally dry had fallen to less than 1% of the region, the lowest percentage since May of 2017.
Annual Precipitation Records
The Midwest as a whole ranked 2018 among the wettest years in its history (1895 to 2018). The preliminary numbers put the region close to 1993, which holds the record for wettest year across the region averaging 42.73 inches. The 2018 total through November was 40.24 inches but the December values were on hold due to the shutdown of the federal government. Using estimated data, it was likely that 2018 will rank 1st or 2nd when the final numbers come in. Several states look to rank in the top 5 for their statewide annual totals as well. Iowa, Kentucky, and Wisconsin will likely rank 2nd wettest, Ohio 3rd wettest, and Indiana 5th wettest. More than 120 stations in the region
(Figure 11) set new annual precipitation records (minimum 30 years of record) with many coming from northern Iowa, southern Wisconsin, northern or southern Illinois, southern Indiana, southern Ohio, and northern Kentucky. Only Missouri had no station set an annual record.
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