“It is one of the most, if not the most surprising events or behaviors I have ever witnessed from the polar vortex,” said Judah Cohen, an MIT research scientist.
Early disruption of the vortex could influence the type of winter weather New England sees, although we might not have to worry about dusting off the snowblower quite yet.
First, what is the polar vortex?
The polar vortex is a massive circulation of strong winds spinning around the Arctic, high above in the stratosphere, 10 to 30 miles above Earth, much higher than the weather systems we experience near the surface.
When these winds are strong and stable, they tend to keep the coldest Arctic air bottled up closer to the pole, by sort of acting like an atmospheric fence. When this band of circulation weakens, stretches, or splits into separate blobs, it can reorganize the jet stream, sending pockets of frigid air south and towards the surface.
It doesn’t mean cold air everywhere, as the jet stream still determines which regions will turn cold and which will remain mild.
Why is this latest vortex disruption so unusual?
Many scientists, including myself, are perplexed by what we’ve been seeing lately.
The latest forecasts show the winds surrounding the polar vortex slowing dramatically, potentially even reversing direction completely by the first week of November. If the winds do indeed reverse, around Nov. 4 or 5, it would beat the earlier seasonal record of around Nov. 28 by roughly three weeks.
“For weather and climate records, that is really unheard of,” said Cohen. “When a temperature record in Boston is broken, let’s say the hottest temperature ever, 106 degrees, and then all of a sudden one day this summer Boston hit 120 degrees, it would be that astonishing.”
This forecast breakdown is very rare because during November, we typically see the polar vortex as stable and strengthening. But the upper atmosphere is experiencing sudden stratospheric warming, in which temperatures surge as much as 50 to 70 degrees in a couple of days high in the sky. This is a direct response to what’s happening at the surface, where large-scale pools of warm air have drifted north and propagated vertically through the atmosphere. In other words, this record-warm El Niño is responsible for producing pockets of intense surface heating that have found their way north and vertically into the upper atmosphere, which is causing the disruption.
Scientists refer to these pools of warm air as Rossby Waves. These waves can crash into the polar vortex, causing it to weaken and sag and the cold air to dislodge and unlock, sinking to the south and towards the surface.
Statistically, the overwhelming majority of Rossby Waves usually occur during January and February. Early November is almost unheard of. Don’t you love atmospheric dominoes?
Forecasts suggest the vortex could split into two main centers, with unusually strong high pressure developing over the polar region.
So is New England going to freeze over?
I don’t think so. Don’t worry about scrambling to dust off the snowblower; there’s an important distinction to be made here.
Even if a polar vortex disruption occurs, its influence may take a couple of weeks, or longer, to work its way down through the atmosphere and affect our day-to-day weather, and New England may be in the clear, at least for the time-being.
That puts the second half of November into early December on the radar. A more disrupted circulation pattern means we’ll see a wavier jet stream, potentially allowing for cold snaps to spill into the Northeast at times. Should a cold snap align with a storm system, then maybe we wind up seeing a bit of early-season snow across the interior.
But we also have to consider the other side of the coin: the jet stream may align where New England ends up in the warm sector more often than not.
I say all that to say this: I just don’t see New England dealing with a deep freeze from this particular event. It’s just too early in the season, and there are too many other warm factors that keep New England away from the significant cold.
And based on what the models are showing, it looks like most of the cold air will be held north of New England and spread over other parts of the Northern Hemisphere, like across portions of Europe and Asia.
I could be wrong, but the puzzle pieces point to us missing out on any epic temperature plunges with this event.
As far as what this early season disruption means for the winter months? Think of El Niño controlling the southern jet stream and the polar vortex controlling the northern jet stream. Based on this super early polar vortex, we may be facing a winter with both warm and cold extremes.
Cohen notes: “If enough and/or long-duration polar vortex disruptions steer the polar jet in New England’s direction, it will be much colder than with just El Niño fully in charge.”
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Ken Mahan can be reached at ken.mahan@globe.com. Follow him on Instagram @kenmahantheweatherman.