We are now officially into meteorological winter (December 1-February 29). Average temperatures continue their tumble, but the rate of the tumble does begin to slow. November sees average highs drop 10-12° while December sees averages drop 7-9° from the 1st to the 31st. How will this month end up shaking out? Read below.
TEMPERATURES
The very start of December will see a continuation of what most of November saw. That is to say that we'll be starting the month off with a brief warm-up with above average temperatures for the first three days of the month. After this warm-up, we'll cool back off next week (December 5).
Much of next week (December 4-8) is currently looking to run below average temperature-wise as New England, and the east coast in general, remains in a trough. This trough does look to shift offshore by the end of next week (December 8-9). Also next week, a ridge is looking to set up across the center of the country with above average temperatures expected across the western two thirds of the United States.
500mb height anomaly showing the aforementioned ridge in the center of the country with a trough centered to New England's southwest on December 6:
With a progressive, zonal pattern in place, this more mild air will likely begin to spread east by later next week (December 8-10), leading to a return to at least average temperatures. This spreading of more mild air across the United States can be seen in the NOAA's 8-14 day temperature outlook (this outlook currently covers December 8-14), which sees basically the entire country more favored to see above average temperatures.
In the 8-14 day outlook, you can see most of New England is in the 33-40% chance range of seeing above average temperatures. This could be a sign of closer to average temperatures as ridging remains centered over the middle of the United States. This means that while temperatures are favored to warm from the below average start, a major warm-up is not expected.
Another item to look at is the NAO Index. The index will start the month in negative territory, a sign of the trough the east will be in next week. After this, the index looks to climb back closer to neutral to slightly positive territory. This would also aid in temperatures warming heading into the middle of the month.
Heading toward the second half of December, forecasts are heavily influenced by the now strong El-Nino. These conditions favor a generally warmer northern United States, with the west and midwest seeing the highest temperatures relative to average. This can be seen setting up throughout this month with warmer than average conditions most likely across the Midwest.
The 3-4 week temperature outlook is very indicative of an El-Nino winter. The main question for New England heading into the second half of the month will be how intrusive cold air shots will be. These shots of cold air were very intrusive into New England in November and if that continues, New England could end up skewing cooler. A positive NAO would help limit the amount of cold air intrusions into the region.
Overall, we're predicting a generally above-average December as a whole, albeit not by much. When all is said and done with December, swings between cooler and warmer than average temperatures (which we also expect) may zero-out and we end up with a near average December. We do believe that both warmer times and colder times will be seen in the month.
PRECIPITATION
After an unsettled start to the month this weekend into Monday (December 2-4), conditions do look to dry out toward the middle part of next week. A trough of low pressure is looking to swing well to the south of New England in the middle part of next week (December 6-7). This track will help keep New England on the generally dry side.
Overall, it's looking like December will feature average precipitation. The general precipitation outlook is once again idicative of an El-Nino winter with drier weather expected across the upper midwest and into the Great Lakes, wetter weather across the south and New England landing in between.
LOOKING BACK
November was a puzzle to figure out, as we stated in our monthly outlook last month. We predicted an average month with brief 2-4 day warm-ups. These brief warm-ups did occur, there was a four day warm-up at the beginning of the month and another one toward the middle of the month. The cool-downs after these warm-ups generally dropped below average rather than back to average, so the month was a bit cooler than we expected.
We also stated that there were some signals of a warmer second half of the month relative to average. We said this would be contingent on whether the NAO Index would be able to climb into a positive range, which it did, but only for a brief time before going negative again. This allowed for another quick warm-up toward the end of the month before more cold air was able to enter the region. Overall, November was a pretty average month with nothing remarkable weather-wise for New England.
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