Meteorological winter has arrived! Meteorological winter lasts the duration of December, January, and February, but as you all know real winter can hit before or after that period. November brought wintry conditions, with our first warning level event for the state mid-month and the coldest Thanksgiving day in recorded history. What does December have in store?
For those new to this SCW feature, I’ll be writing every two weeks (or just about) to provide you with a broader and longer term outlook on the weather in the region. This will be my fourth year doing it, and overall, I’ve done well with these. As an added incentive to do well, I grade my performance. Here’s to a lot of A’s this winter!
Unlike the usual forecasts which use operational models, the main tool used my outlooks are the ensembles. Ensembles are the operational runs of the major models which are tweaked with different conditions. This (ideally) helps resolve the inherent uncertainties that grow in time during a forecast period.
Although I’m not making the usual sensible daily weather forecast, it is my hope that I’ll be able to provide enough detail about potential to help you plan ahead.
Before we jump into the first outlook, it’s important to understand what normal, or “climo” is.
When I say climo I am simply referring to weather conditions averaged over a period of time, usually using the data between 1981-2010. Climo gives you a sense of what you could expect on average. It keeps us that don’t like hype tethered to reality. That said, things can and do fluctuate, sometimes significantly as patterns change.
Overall in December, CT usually sees its first significant snowfall (greater than 1”). It not always a guarantee and the second half of the month tends to be the best shot for wintry weather. Again, even in a great pattern in December, a lot of Connecticut (especially at the coast) can end up with events that are rain or mix.
BDL (Bradley Airport)
Dec 1 avg high—45
Dec 1 avg low—29
Dec 31 avg high—35
Dec 31 avg low—19
Dec avg snow—7.4”
Dec record snow—45.3” (1945)
Dec 1 avg high—47
Dec 1 avg low—33
Dec 31 avg high—38
Dec 31 avg low—24
Dec avg snow—5.1”
Dec record snow—16.0” (1948, when records are first available at this location)
With that refresher, it is time to talk about the first half of December.
* Note—high confidence (70% “sure”), moderate confidence (45-69%), low confidence (0-44%); nothing significant (less than 1” snowfall and .25” ice)
Week one—Saturday December 1 to Friday December 7
Temperatures—below average (high confidence)
Precipitation—average (moderate confidence)
Wintry Precipitation—below average (moderate confidence)
The first week of December will begin with a rainstorm that should bring us to average precipitation for the period. The first Sunday of the week will be above normal as well. However, the majority of the week will be decidedly below normal in temperatures. There are no strong indications of a significant winter weather event this week.
Week two—Saturday December 8 to Friday December 14
Temperatures—average (moderate confidence)
Precipitation—average (low confidence)
Wintry Precipitation—average (low confidence)
Week two is a bit more complicated, as a signal for a significant storm is already appearing for the beginning of the forecast period. It is too soon to say whether that system would be rain, snow, or even impact the region. Temperatures will start off colder than normal, but should begin to warm up as we see a pattern change that will end the multi-week pattern of colder than normal temperatures. There may also be a signal for a rain event at the end of the forecast period.
The first day of December has a Winter Weather Advisory in effect for northern Litchfield County, which has seen quite a bit of winter recently with daily snowfall in spots. For most of Connecticut however, the first weekend of December will be wet and warm as a low traverses the region. In the wake of this low however, we will see another push of colder than normal air, as the PAC and Atlantic pattern remain favorable for cold air delivery. The majority of the work week as a result will see high temperatures that are below normal.
Toward the end of the week, some of the guidance is hinting at the potential for some snow showers on Friday, but that’s a low probability deal currently and has a low ceiling for amounting to much. What once looked like a promising period for wintry precipitation in the middle of the week has evaporated entirely.
Below, you will see the GEFS 7 day precipitation anomaly. After the rain this weekend, I expect a quiet period until the next forecast period.
The second week and next forecast period is the one that snow lovers and warmth lovers alike will be watching. The period is likely to begin with us watching a significant storm developing in the south. All options are on the table when it comes to the track, including a total whiff. The signal for a developing storm is a strong one. In the wake of that system, we start to see a pattern shift with temperatures, but the relatively stormy pattern continues with another rainstorm possible by the end of week two. That system is far less likely to develop at this time, and as a result, we could easily see below normal precipitation possible.
As for temperatures, things shift significantly, as we begin to see that broader pattern shift that I mentioned earlier. The teleconnections shift, especially the Pacific pattern.
Overall, this has the potential to be a solid start to December both for winter lovers and winter haters. We will see our fair share of cold and a likely mild up at the end of the two week forecast period. For snow lovers there is a chance of a system impacting the state at the start of week two, and for rain lovers…well, I don’t know if there are rain lovers but we may have our chances. Remember, even a great pattern does not guarantee snow for anyone in Connecticut this early in December.
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