Meteorological winter begins December 1 — here’s what to expect

December 1 marks the start of meteorological winter, so it’s a good time to take another look at the month ahead. Coincidentally, as if right on cue, the first winter weather advisory of the season for the possibility of freezing rain is posted for western Massachusetts.

The Return of Messy Storms
One of the elements of winter I think we will see much more of this year, as compared with last, is mixed precipitation, freezing rain, and the rain-snow line. I am basing this on fewer arctic outbreaks and more frequent intrusions of warm air during stormy periods.

Why It’s Winter for Meteorologists
The next 12 weeks are the coldest and typically snowiest of the year. Although March can bring plenty of cold and snow, December to February is considered the core of winter. March is more of a fickle month, usually starting wintry and ending more spring-like. This is why meteorologists mark winter beginning today.


There are a few predictable aspects of December: On average, our temperatures typically fall another 8 degrees. Afternoon highs run in the 40s at the start of the month and 30s by the end. Daylight shrinks to its shortest levels at the beginning of the third week, before gaining back a few minutes by New Year’s Eve.


sunrise boston.png


Because of the Earth’s shape, you may be surprised that, based on your location and the Earth’s orbit, the earliest sunset and latest sunrise aren’t actually on the winter solstice. Our earliest sunset is December 9, while the latest sunrise is January 4. (Technically, our latest sunrise was October 31, but that was due to Daylight Savings Time.)

A Snowy December?
Snowfall in December is highly variable. While the average snowfall runs from about 9 inches in Boston to over a foot in Worcester, each year brings very different results.

The chart below shows how much snow has fallen seasonally since the early 1990s. Notice December, which has an enormous range in terms of accumulation. This year, due to a strong El Nino, arctic air being locked up in Canada, and other non-favorable winter patterns, I expect December to see less snow than average — especially the first several weeks of this month.



december snow boston.png


December 2015 and Beyond
Most of the models agree: December is going to be a milder-than-average month overall, and the stormiest weather will be south of New England. The odds heavily favor significantly less snow than average, too.

Check out the three maps below. The first shows predicted temperatures for December. Notice the Northeast is forecast to have above-average readings.


warm december.png


The next map is for precipitation. What’s interesting is the wetter-than-average prediction across the Southeast, and the average-to-drier-than-average forecast in New England. This is a similar pattern to the fall. More to come about the snowfall forecast, but my quick prediction is average to below average snowfall this season, but not above.


wetter soput sdf 2.png


Finally, I’ll leave you with the latest prediction for the overall three-month period of December through February. Once again, we see the overall numbers, when averaged on March 1, should be warmer than average. This, of course, doesn’t mean there won’t be several cold periods within the next three months, but the odds continue to favor a very different winter than the one we had a year ago.


warmer than average.png


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