As we wrap up fall, these recent cool nights and crisp days start to raise the question: What kind of winter will New Englanders see this year?
Meteorological winter, which stretches from Dec. 1 through the end of February, can usher in the most variable weather of the year, from warm holidays and flooding rains to nor’easters and arctic polar freezes. With our changing climate driving temperatures generally higher, our weather systems and their duration, intensity, and impacts can certainly fluctuate.
And this year most signals suggest New England will experience yet another warmer-than-average winter with pretty much above-normal precipitation like last winter. But competing forces and a weak La Niña will likely make for some inconsistent weather, injecting bursts of cold, arctic air in between streaks of warm winter days. So if a weather system lines up with a pocket of cold air, this can certainly produce more snowstorms than winters past because La Niña is known for more erratic patterns.
Last year, the Boston area had one of the warmest winters on record (Vermont and New Hampshire had their warmest), and as a result, one of the least snowiest as well. Boston saw a steep drop from the average snowfall, picking up a measly 9.8 inches, the fourth-lowest snow total on record, dating back to 1890. The previous year, winter 2022-23, also a mild season, generated only 12.4 inches of snow.
For nearly a decade, the average winter temperature in the Northeast has been well above normal, with the last two seasons seeing the thermometer soar at least 2 degrees above average in many areas. The Boston metro area jumped about 4 degrees higher during the past two winters.
Below you can see the trend of warmer-than-average temperatures in recent years during Boston-area winters.
The La Niña conundrum
Any increased development of a La Niña will impact our winter here in New England. La Niña is the opposite of El Niño, where sea-surface temperatures off the western coast of South America in the Equatorial Pacific Ocean are cooler than average. This occurs when the westerly trade winds at the equator become stronger than normal and push surface water well to the west. That water needs to be replaced, and is done so by cooler water rising from the depths of the ocean.
“When the pattern is active, it can shove around atmospheric patterns in a somewhat predictable manner,” said Michelle L’Heureux, a meteorologist with the National Oceanic and Atmospheric Administration (NOAA). The stronger the La Niña, the easier it is to forecast storm frequency and track.
“If there is a weak or lack of La Niña, the forecast crystal ball becomes more blurry.”
With a La Niña, the jet stream is often displaced to the north and can result in cooler and wetter conditions across New England, especially away from the coast — meaning more snow for Vermont and New Hampshire.
But as of now, NOAA’s Climate Prediction Center is calling for a 60 percent chance for a weak La Niña to develop ahead of winter and persist through March 2025. The forecast trend for a winter La Niña has actually been decreasing over the last few weeks.
“We only consider it a La Niña event if the below average sea surface temperatures last at least five overlapping months, and this one should just barely make it,” L’Heureux said.
What does this tell us?
Meteorologists often compare years where similar conditions were present to support their forecasts, and the last time there was a weak, short-lived La Niña heading into winter after a more neutral summer was the winter of 2016-17.
Simply put, any La Niña influences were negated that season. Average temperatures across the Northeast ended up being the seventh warmest on record while all six New England states finished with a Top 10 warmest winter season.
Even precipitation didn’t see the typical La Niña boost, with New England staying slightly below the norm. The exception was Maine, which saw slightly above-average numbers.
This means interior sections of New England, like Vermont and New Hampshire, could see more La Niña cool and wet conditions, making for some nice snowy ski resorts this winter.
The Boston area sees 37.7 inches of snow on average from December through February, according to Matthew Belk, meteorologist at the National Weather Service in Norton. “Though a higher probability of above-normal temperatures does not mean that snow is not possible at all for Boston. It just will really depend on timing of individual events,” like snowstorms.
Other impacts
Looking outside of La Niña’s potential impacts, it’s very hard to ignore the alarming trends of climate change that will play a major role this season.
The atmosphere and oceans continue to trend warmer. Hotter oceans evaporate more water and a warmer atmosphere can hold more water vapor — all resulting in more available potential precipitation across the region. These trends strongly influence the forecast and suggest that with more moisture in the atmosphere, there will generally be above-average heat and precipitation this winter.
“Last winter’s average temperatures for the Northeast were the warmest since record-keeping began in the late 1800s,” said Jessica Spaccio, climatologist at the Northeast Regional Climate Center. “The average for the region was nearly 8 degrees warmer than the 20th century mean and nearly 5½ degrees above the 30-year normal.”
Last winter also marked the first time on record where the average temperature for winter in the northeast stayed above freezing, 32.1 degrees. Only four winters since 2000 were below the 20th-century mean, as seen below.
A similar pattern can be seen with the overall increase in precipitation across the Northeast since 2000.
Storm track and intensity
A warmer-than-average ocean can certainly influence individual storm track and intensity — especially with waters across the Northern Atlantic continuing to set daily record highs leading into winter.
Coastal storms can gather more strength over warmer waters. A La Niña winter usually reduces the number of coastal storms and nor’easters by shifting the jet stream away from the coast. But La Niña or not, a warm ocean and atmosphere can easily create a system that can blow moisture-rich air from the North Atlantic onshore, amplifying heavy rain, snow, and wind.
When was Boston’s last snowy winter?
Boston hasn’t seen an eyebrow-raising winter since the record-setting 2014-15 season, when nearly 100 inches of snow fell. The strange part? We were in the depths of a prolonged El Niño event — the exact opposite of what is likely to come this season.
Ken Mahan can be reached at ken.mahan@globe.com. Follow him on Instagram @kenmahantheweatherman.