It has been a cold start to winter in Pennsylvania with most of the state running a few degrees below average in December. Although a few mild and wet days to end the month may return anomalies to near normal. But what is in store in January is a different animal.
It has been a decade since we had utterly frigid air sustain itself for a long period in the heart of winter, but that streak looks to come to an end. There are a variety of indicators around the globe in the form of mostly sea surface temperature anomalies and height anomalies that determine our winter pattern.
You have likely heard of La Nina, but there are other indicators that change on a weekly basis, which explains our roller coaster pattern every winter. But all at once these indicators, or teleconnections as we call them, will heavily favor colder than normal conditions in the eastern half of the United States in January.
And we’re not just talking a few days of frigid temperatures followed by a warm up. All model guidance points to a minimum two week period of solidly below average temperatures, with a decent possibility of continued negative temperature anomalies through the end of January.
After New Year’s Day, we will be on a constant descent into Arctic air. Here is a look at the European model’s ensemble mean (50 individual models combined into one) for the 10 day period from January 2nd – 12th. Actual temperature departures will be even colder than this mean.
For a more practical example, we can look at the European model for around January 10th, which has high temperatures in the single digits and teens and lows on either side of zero degrees across PA.
Below is a look at low temperatures on January 11th. The only thing that may change this is if there’s a snowstorm, and in that case we would be a little warmer before diving into dangerously cold air.
Showing temperatures on a model 14 days out is much different than showing a winter storm. This is because temperatures are determined by the vast number of indicators we talked about earlier, whereas winter storms have many moving parts that can’t be accurately modeled more than ~5 days out.
All teleconnections (indicators) can do with regard to snow is tell us whether the pattern will be favorable or unfavorable for snowfall in the Eastern US.
Almost always we have mixed signals with some favorable indicators and some not so much, but this period has the green light from all indicators. But teleconnections cannot narrow down how much snow different areas of the state will see.
We already have a few winter storm signals showing up during the second week of January, around the 6th and the 10th. Realistically, if they both hit, the first may be more of a wintry mix. Whereas if the first signal is mainly snow, the second may be too far off the coast and we will be stuck with Arctic cold and dry air.
At this range, forecasters use tools like the European ensemble runs to determine winter storm signals and general temperature and precipitation anomalies. The last thing anyone wants, besides perhaps ski resorts, is a cold and dry pattern.
The Euro ensemble package, along with other models like the American and Canadian, has been enthusiastic about the pattern being relatively active for such a cold period.
Below you will see the European ensemble model’s snowfall projection for the next 15 days. All of this falls after the New Year. This is a very impressive mean for a period with no snowstorm already locked in.
And that is also the key. We have winter storm signals, but nothing more. Time will tell what happens, so the map below is used only to tell us that snowfall anomalies are favored to run above average for the first half of January, as these numbers are about 33% above average for that period.
Details aren’t as clear for late January into February. We have a full-fledged La Nina now, which is a new development in the last few weeks. That may not bode well for snow lovers in February and March.
However, a pattern like this one upcoming is not easy to get rid of and we do not expect a transition to a torchy, snowless pattern come February. But those details will be worked out later, at a point in which many of us may be exhausted by the bone-chilling cold.
For now, we recommend making sure your snow blower still works, and preparing for temperatures that will require multiple layers of clothing if you plan on being outside for more than 10 minutes.
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