A Connecticut winter never fails to surprise. In the last decade alone we have seen wild swings in winter weather from some of the warmest on record, to some of the biggest snowstorms.
How we made the forecast:
When attempting a winter forecast, meteorologists look at global weather patterns. One of the biggest factors can be the "El Niño – Southern Oscillation (ENSO)."
We’re talking about the water temperature thousands of miles away, in the equatorial Pacific. But this phenomenon can affect the weather on a global scale, including right here in New England.
When the water is warmer than average it’s called El Niño and it can mean the kiss of death for winter lovers in New England (like 2015-2016 when we only got 27” of snow). But this year, NOAA is forecasting a weak (to borderline moderate) La Niña with cooler than average water temperatures in the equatorial Pacific.
Unlike El Niño, a weak La Niña does not have a clear-cut impact on our weather in New England. I looked at data from past weak La Niña years in Connecticut and found temperatures were generally within a degree or two from average. However, there was QUITE a range in snow totals from 10” in 1954-1955 to 70” in 2005-2006. Basically, it wasn’t too helpful in steering me one way or the other.
So, I also tried to look at past years that featured a warm September and October followed by a cold November. In addition I wanted to look at years that featured a blockbuster hurricane season. My goal was to find similarities from the past (we call these analog years). No past years perfectly matched but I was starting to see a pattern.
In those years, winter hinged on one big wildcard, the North Atlantic Oscillation (NAO). If the NAO is negative, a cold, snowy winter is favored with more east coast Nor’easters. Unfortunately it's hard to forecast the NAO with skill more than a couple of weeks out.
Another clue that we can draw from is the amount of snow cover in Siberia. This fall, it’s already piling up and research shows in past years that can favor a snowy and cold winter in the eastern US (from a negative arctic oscillation).
Compared to last year, it looks like there will be more opportunities for blocking and arctic outbreaks. But there are no clues pointing towards a brutally cold winter either.
The 2017-2018 Winter Outlook:
Overall, we are forecasting a volatile winter with changeable temperatures, cold shots followed by periods of milder weather. This winter will be colder than last year (by a lot in comparison, 2016-2017 was the 10th warmest on record) but temperatures will finish near seasonal averages.
The battle between cold and milder temperatures should set the stage for an active season with plenty of clippers and coastal storms. In terms of snowfall, we’re forecasting an above average season. This is similar to last year and the opportunity for decent snow continues into March.
The skill in long-range forecasting is fairly low. Forecasting 7 days out can be a challenge in itself! Plus a lot of the conditions that we need to forecast a big storm can only be seen in the short-term. That’s why I’m not going to give you exact snowfall amounts. I find this gives a false sense in confidence.
BUT it is interesting to look at the overall trends for clues.