Nine of the past 10 years have brought remarkably warm Decembers to Minnesota.

December 2015 was the warmest in state history (back to 1895) with a statewide mean temperature of nearly 25 degrees F, about 12 degrees above normal. In addition, the Decembers of 2011, 2014, 2018 and 2020 rank among the 20 warmest months of December in state history.

Statics show this to be a highly unusual in that we have not had a series of Decembers anything like this in the past. The only December in the past 10 years that brought cooler-than-normal temperatures to Minnesota was in 2013. That one was strikingly cold, delivering some temperatures ranging from -25 to -40 degrees during the last week of the month.

Within the statewide climate station network, the number of record-warm daily maximum and minimum temperatures set during the months of December 2011, 2014, 2015, 2018 and 2020 is astonishing. There were 367 daily warm maximum temperature records set, including several days over 50 degrees. On Dec. 19, 2011, Madison (Lac Qui Parle County) reported an afternoon temperature of 60 degrees, an all-time statewide record for the date. Residents of western Minnesota enjoyed taking their lunch outside in the sunshine that day.

There were 866 daily warm minimum temperature records set during December of those years as well, with many overnight minimum temperatures remaining above freezing, and in several instances even above 40 degrees. Some area lakes did not form ice cover until after the new year.

With a La Niña episode (cooler-than-normal ocean surface temperatures in the Equatorial Pacific) currently in place for the winter of 2021-22, it will be interesting to see if the historical La Niña correlation with colder-than-normal Decembers in Minnesota holds up. Because it is not a particularly strong episode of La Niña, I suspect that the long-term warming trend evident in the December climate data of the most recent 10 years may override the historical correlation of cold weather with La Niña. The other possibility is that the colder-than-normal winter weather pattern in Minnesota associated with historical La Niña episodes may not emerge until the month of January. This may actually be the more likely scenario to look for. We will see what happens.

Seeley is an Extension professor emeritus of meteorology and climatology at the University of Minnesota.