Polar vortex shift poised to unleash more bitter cold across the US through mid-December
More Arctic air is building over northern Canada and will be directed into the United States, courtesy of the polar vortex. How long will the cold waves last? Will it stay cold through Christmas?
Frigid air delivered by a polar vortex caused Lake Michigan’s spray to freeze into dramatic icicles on the St. Joseph North Pier in Michigan on Dec. 4, as temperatures plunged toward near-record lows overnight.
Long after one blast of Arctic air pushed offshore last week, a new surge of cold air, driven by a breakdown of the polar vortex, expanded from central Canada and to the Midwest on Sunday and will finish up on the Atlantic coast on Tuesday. However, already a new blast of Arctic air is building and will sweep through much of the eastern United States later this week.
The Arctic blasts won't stop there, as more cold waves could follow before the cold waves diminish after the middle of the month, AccuWeather long-range meteorologists say.
The polar vortex is a large upper-level, low-pressure area or circulation that typically resides above the Arctic Circle.
When this circulation is strong, it tends to keep the coldest air in the Northern Hemisphere locked up over the pole. However, when it weakens or stretches, frigid air can move south.
"The polar vortex has been in a weakened and stretched state since late November," AccuWeather Lead Long-Range Meteorologist Paul Pastelok said. "We are seeing the result as Arctic air pushes southward across the central and eastern U.S. in recent days and may continue to do so for the next couple of weeks or so in waves."
When does the next round of Arctic air arrive?
The next big surge of Arctic air is expected to advance from the northern Plains on Thursday to the Midwest on Friday and then to the East on Saturday. This cold blast will follow a midweek clipper storm, which is expected to spread snow from the northern part of the Plains to the Midwest and the interior Northeast.
"We believe that two to three more rounds of intense cold are possible from the Midwest to much of the East, spanning Dec. 10 to 19," Pastelok said. "There is a chance for a frost or freeze late next week as far south as central Florida."
With long nights and only weak sunshine this time of year, temperatures can tumble quickly and remain low for an extended stretch. Each wave of cold air has the potential to be colder than the previous one in many areas of the Midwest and Northeast, especially where fresh snow is on the ground. For example, just Thursday morning, New York City hit its season low mark of 24 degrees in Central Park.
Even the Southeast may experience episodes of cold air.
Temperatures are projected to dip into the teens next week. When and where the wind is blowing, along with other factors, the AccuWeather RealFeel® Temperature can be 10 to 20 degrees lower than the actual temperature.
Snow, wintry mix forecast for millions
Accompanying many of the waves of Arctic air are likely to be patches of steady snow and episodes of flurries, snow showers and heavier snow squalls—all of which can make roads slippery and lead to travel disruptions. As the temperature drops behind each snow event, especially later in the day and at night, untreated wet areas can freeze into a thin sheet of ice.
"The fast movement of the waves of cold air will generally prevent giant snowstorms from developing," Pastelok said. "However, the best chance for a rapidly intensifying storm on the East Coast would be late this week to next week, as an Alberta clipper storm may slow down just enough as it reaches the Atlantic to grab extra moisture."
Such a storm could bring enough snow to require shoveling and plowing to heavily populated cities in the mid-Atlantic or New England.
Less cold possible for some during 4th week of month
Pastelok added that the cold may ease up by the week of Christmas.
"That will depend on the next weakening of the polar vortex around Dec. 14. La Niña conditions for the last 10 days of the month are anticipated with more wet and snowy weather for the Rockies and Northwest, perhaps even a couple of storms reaching Southern California," Pastelok added.
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