Is a polar vortex plunge in store for northeastern US this winter?
By Alex Sosnowski, AccuWeather senior meteorologist
January 08, 2019, 12:52:17 PM EST
The cold targeting the northeastern United States later this week is a "warning shot" for winter's return late in the month and early February.
Arctic air is likely to only periodically brush areas from the Upper Midwest to the Northeast over the next couple of weeks. The northern parts of these areas will continue to receive rounds of snow. The combination of snow and periodic cold will create good skiing conditions.
Farther south, it's a different story with mild conditions and little to no snow.
"However, a major stratospheric warming event has begun," according to AccuWeather Senior Meteorologist Brett Anderson.
The stratosphere begins at around 4 miles above the ground near the poles to about 12 miles above the ground near the equator.
When the stratosphere warms suddenly over the North Pole, it weakens the polar vortex and causes the normally pent-up frigid air to be displaced southward over one or more continents of the Northern Hemisphere.
Following a sudden stratospheric warming event, lobes of the polar vortex may also shift southward with the jet stream which can enhance the impact of the frigid air by adding strong winds.
"The discharge of frigid air is not always immediate," according to AccuWeather Lead Long-Range Meteorologist Paul Pastelok.
What is a polar vortex?
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"In order for a frigid pattern to be set in motion for the Northeast, we need the jet stream to bulge northward over northwestern North America, which would then shut off the flow of mild, Pacific air across much of the nation like we have going on now."
Cold air is anticipated to plunge into the Northeast later this week and hold into next weekend. Typical January cold is anticipated for most areas these days.
"The late-week cold shot should fade next week, but this is a warning shot for winter's return late in the month and early February," according to AccuWeather Long-Range Meteorologist Joe Lundberg.
For now, AccuWeather's long-range team is expecting a significant downturn in temperatures in the Northeast sometime during the third or fourth week of the month but stopping short of a close encounter with the polar vortex.
This will follow another dose of cold air during the third week of the month over the North Central states. The cold weather there may be similar or more substantial to that which occurred during the week of Christmas.
During the latter part of January, temperatures may shift from generally at or above average to slightly or significantly below average in the Northeast as that cold air from the North Central states tries to work eastward.
Average highs during late January in the Northeast range from near 20 F across northern Maine to the upper 30s around New York City and the upper 40s in southeastern Virginia.
Download the free AccuWeather app to see what the long-term temperature trend is for your area.
Substantial cold weather is still anticipated during February. How severe and long-lasting the colder weather is may depend somewhat on the southward position of the polar vortex and the extent of snow on the ground.
A thick snowcover tends to reduce the warming effect of the sun. Some of the most brutal and long-lasting cold outbreaks have taken place when there is an extensive snowcover.
"There is currently very little to no snow on the ground from the Ohio Valley to the mid-Atlantic and southern New England," Pastelok said.
"We expect some double-digit temperature departures from average for a couple of days here and there during February, based on a storm or two that may put some patches of snow down."
If a large storm with extensive snow were to come about during late January to early February, the cold air that follows could be more severe and longer-lasting.
AccuWeather's winter forecast, which was released during the late summer of 2018, did not call for a significant and long-lasting downturn in temperatures until late January and more so during February for the eastern U.S.
At this point, people from the Great Lakes to the Northeast should still expect late January to February to feel like the middle of winter.
Listen to Everything Under the Sun’s host Regina Miller as she discussed the Blizzard of 1996 with two AccuWeather Expert Meteorologists, Dave Dombek and Paul Pastelok who were on hand during that paralyzing storm. Learn how forecasts were prepared back then and how technology has changed over the years, allowing for more accurate forecasts and dissemination of our weather forecasts and warnings.
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