A Very Mild December Expected

Long range predictions are in excellent agreement that December will be milder than average across the Midwest. This will be due to an upper level jet stream pattern that will likely prevent very cold airmasses from moving into the region, and any seasonably chilly airmasses from lingering for more than a few days. The expected pattern is typical in strong El Nino episodes, such as the one that is currently ongoing. The Climate Prediction Center (CPC) has indicated a 70 to 80% chance for the average December temperature to finish above normal across the local area in its latest December temperature outlook (top image on graphic).

Climate models such as the Climate Forecast System (CFSv2) run by the Climate Prediction Center can give increased confidence in a monthly forecast. These models can exhibit significant day to day variability leading up to months characterized by more complex and less predictable weather patterns. However, every single daily run of the CFS model has forecast well above normal temperatures in our area for December. The bottom right image on the graphic is a snapshot of the last 9 daily runs of the CFSv2 for December surface temperature anomalies (11/22 - 11/30). The brown-gray colors consistently predicted for our area by the model are indicative of the potential for temperatures to average 3 to 4 degrees Celsius above normal, which would equate to 5 to 7 degrees Farenheit above normal if the model verifies well.

None of this means we won't see any bouts of typical winter cold and snow in December. However, the overwhelming evidence is in support of a mild month temperature wise, so the mild days are expected to far outnumber any chilly days.

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Castro