February 6, 2023

This winter we expect a frigid air to affect the weather in New England. But to understand whether it’s going to be very cold here or bring a lot of snow, you need to understand some climate science.

And the thing is, climate change is making it harder and harder to do that. Here’s how we approached this year’s Season Prediction:

How the polar vortex works

In our Climate 2022 climate change special that cites this article, one of our segments featured an interview with Dr. David Coe, whose PhD at the University of Massachusetts, Lowell, focused on how climate change has altered the winter season in New England and across the Northern Hemisphere.

For generations, the polar vortex has been a consolidated pool of intense cold and atmospheric energy near the North Pole.

The first key term to explain the winter season change begins with the polar vortex.

Yes, in 2014 the polar vortex almost became a joke in the mainstream media — reporters stood outside and smashed slices of frozen pizza, eggs, steak, or frozen T-shirts at flagpoles, the ground, or themselves. But the scientific reality of what What happened back then and what regularly happens to the polar vortex in modern winter is anything but funny.

The polar vortex isn’t new — it’s a recurring feature in the atmosphere, present to some extent year-round, but most commonly in winter as a counterclockwise swirling mass of cold air and atmospheric energy at high altitudes that is usually located somewhere near the North Pole. Every winter for generations, as the vortex tumbles south, or sends some of its cold energy south, it is followed by a gust of considerable cold air—this is well known among meteorologists.

Still, most of the cold air would remain near the polar vortex, with temperatures of 10 and 20 degrees below zero and colder in the Arctic and northern Alaska.

But in recent years – 2014 certainly the first, most visible example – the polar vortex has been attacked by heat from all sides.

What happens when heat enters the Arctic isn’t just a melting of glacial ice caps. The polar vortex breaks through a deep layer of the atmosphere in response to warming temperatures, unable to hold together a pool of constant cold. As the vortex breaks into pieces, each of these smaller pools of cold air becomes unstable, wobbles, and plunges southward—further south than an intact and complete polar vortex would normally do.

These fractured pools of intense cold are delivering sub-zero temperatures to areas farther south than normal, leading some to wonder how much global warming is really taking place. What they may not realize is that heat is pouring into the Arctic to take the place of the disjointed and fractured polar vortex. Farther south, those unaffected by the migrating cold Arctic air basins are experiencing warmer than normal weather in response to the warming climate surrounding these extraordinary basins.

A warming globe has caused the fracturing of the polar vortex most winters.

This breaking up of the polar vortex affects not only the temperature but also the snow. The explanation here is one of the most basic elementary school concepts that clouds and precipitation are formed when cold and warm air collide with moisture.

Consider this: if the ground state, which is most of the air and water, warms, it means both warmer temperatures and more moisture in the air. Now we are introducing a southward-moving pool of intensely and unusually cold air – a slice of the polar vortex – into the generally warm air. The result is an exceptional clash of heat and cold, meaning the potential for an exceptional snow zone.

As storms develop on the periphery of displaced Arctic cold and atmospheric energy, these storms are fueled by the warm-to-cold temperature differential and tend to develop over and over again along the same storm path where cold and heat collide. That means snow keeps falling on the same area, similar to what we saw in the Boston area in February and March 2015 when we broke our seasonal snowfall record in a matter of weeks.

Again, some just below the snowy zone may question whether winter is truly fading, but those not below see the evidence in the form of above-average temperatures and rain, or mixed precipitation events with below-average snowfall.

Fragmented, migrating bubbles of intense cold result in repeated blizzards in the same areas.

climate change and prognosis

This modern winter pattern poses a challenge for forecasters, who are taking seasonal forecasts from an already questionable rate of accuracy to a near-futile rate. In essence, modern winter forecasting is this: Predict when the polar vortex will be fractured by heat entering the North Pole, and then accurately predict where those fractured cold pools will end up.

If you can do that, you can pinpoint where the narrow, repeating, heavy snow bands will develop, and you can pinpoint the small areas that will confirm a colder-than-normal winter, knowing that almost everywhere outside of these zones is warmer will be-than-normal.

The problem is that some of this polar vortex breaking can be caused by one, two, or a few powerful storms that are successful in carrying heat to the Arctic, and it is nearly impossible to predict the presence, trace, and intensity of these storms over months to predict.

The additional challenge is that we have by and large lost the value of so-called analog forecasting. Finding a match in the forecast means going back several decades into previous years and finding comparable weather patterns: similar jet stream patterns or seasonal patterns leading into winter, and exploring what happened in those winters.

The problem is this: Back then, you were dealing mostly with a standard winter pattern that had an intact polar vortex that was fairly stable. Introducing a splintering, wiggling, fractured polar vortex and even flooding the arctic atmosphere with heat just isn’t something we have many analogies for. As a result, you can look at large-scale atmospheric and oceanic patterns and certainly develop a “ground state” of how the atmosphere should work, but forecasters must be prepared to be horribly misled by historical analogies that just don’t do it anymore fit.

For example, the winter of 2022-2023 occurs in a La Niña pattern that features colder than normal seawater temperatures in the Pacific Ocean near the equator. As you can imagine, a vast body of ocean water like the Pacific that is either warmer or cooler than normal over a large enough area can alter oceanic and atmospheric patterns on a larger scale.

In the words of First Alert meteorologist Pamela Gardner, “La Niña is expected to be developing for the third consecutive year. If we look back at the past La Niña years, we were pretty close to “normal” snowfall. The North Atlantic Oscillation has been negative and is expected to be neutral to slightly positive. So that means colder than normal temperatures here and a more coastal, stormy route.”

Pamela’s reference to the North Atlantic Oscillation is a nod to another large-scale pattern that helps provide a likely ground state for the atmosphere. The NAO refers to changes in the magnitude of atmospheric pressure over the North Atlantic – low pressure near Iceland and high pressure near the Azores. A negative NAO means both are fairly weak, often corresponding to cold New England conditions.

As for La Niña, New England often sees warmer than normal conditions and more mixed precipitation events than snow.

Winter forecast for New England

How do we bring all this together?

Our First Alert team believes that the combination of all of these factors increases the likelihood that one of the fractured parts of the polar vortex, with its intense cold, will settle somewhere near southern Hudson Bay and James Bay in Canada, and stretch as far as Ontario and Quebec extends. This would mean the incursion of extraordinary cold into these areas.

With New England not far away as the crow flies, cold fronts strong enough would unleash shots of that intense cold to open up into New England, with northern New England obviously being more vulnerable. The end result is likely that New England will be warmer than normal overall this winter season, as heat tends to flow north during a La Niña year, with southern Canada being colder than normal and northern New England having the highest potential to approach normal temperatures for the time of year – although the North Country is also likely to get warmer than normal given the consolidation of polar vortex fragments.

Our First Alert team believes this year’s weather pattern will favor intense cold weather for nearby residents of Ontario and Quebec.

If this temperature forecast is correct, it may be difficult to establish the recurring snow zone over southern New England, although somewhere between southern Canada and southern New England would make the most logical sense, with southern Ontario and Quebec perhaps in the far north country of New England being the most likely Area for setting up this repeating snow track.

This wouldn’t mean no snow for southern New England — in fact, an active storm track with occasional shots of deep chills can cause snow to accumulate on the front end of several storms — but a tendency for southern New England, toward mixed precipitation tends to trend over the course of each event, limiting the likelihood of a winter with above-average snow.

All that said, for the sake of the impact of changing climate on our northern hemisphere winter weather pattern, our First Alert team approaches the winter forecast with exceptional humility and an understanding that much of it is more educated guesswork than ever as we work on it working to pinpoint the location of a splintering polar vortex.

A changing climate certainly means that we trust monthly forecasts (see our December monthly forecast) more than seasonal ones.

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