by Kristina Pydynowski
Senior Meteorologist for AccuWeather.com
AccuWeather Global Weather Center
AccuWeather.com reports last week's thaw was a mere tease for the Midwest and Northeast with the polar vortex set to make an encore performance this week.
The stretch of mild weather across the Northeast came to an end with the weekend after temperatures rose into the 60s in Washington, D.C., and into the 50s in Philadelphia, New York City and Boston.
Highs on Monday were 10 to 20 degrees colder throughout the Northeast and mid-Atlantic following the passage of a band of rain and nuisance snow on Sunday night.
Colder air has already erased the mild spell across the Midwest, and Sunday should prove to be one of the "warmest" days of this week.
Waves of even colder air will pour down from the depths of the Arctic to the northern Rockies, Midwest and Northeast as this week progresses and the polar vortex plunges southward.
Each cold blast will dip into the southern Plains and south, leading to some cooling. However, the core of the polar vortex will have a firm grip on the northern tier of the U.S.
"The polar vortex is essentially a mass of very cold air that usually hangs out above the Arctic Circle and is contained by strong winds," said AccuWeather.com Senior Meteorologist Alex Sosnowski.
Under the grip of the polar vortex, the Upper Midwest, Great Lakes and St. Lawrence Valley will endure several days in the teens and single digits. This includes Minneapolis, Chicago, Detroit, Montreal and Buffalo.
Overnight lows well below zero, even approaching 30 below zero near the Canadian border, will dominate the upper Midwest.
Temperatures will even be held below zero during the daylight hours on one or more days in Winnipeg, Canada, Fargo, N.D., and St. Cloud, Minn.
Subfreezing highs in the 20s and lower 30s will be common throughout the Northeast. In late February, such highs are 10 to 20 degrees below normal.
Bouts of gusty winds ushering in the frigid air will create even lower AccuWeather.com "RealFeel" temperatures.
"One reason for the cold blast carrying more weight than you might expect is the fact that the Great Lakes are largely frozen over," Sosnowski said. "The air will not moderate to the extent as if most of the lakes were not frozen. In addition, while the amount and extent of the snow on the ground has diminished, many areas north of I-70 have retained some sort of snow cover."
With fresh snow also re-entering the picture, some communities will have snow cover once again increase.
Initially, nuisance snow events with amounts generally on the order of a coating to an inch or two will streak across the Midwest and Northeast through Tuesday.
The greatest chance of snow in the Northeast - including the I-95 corridor from Washington, D.C. to Boston - will come on Wednesday as a low tracks off the East Coast.
Although accumulations are expected to be on the lighter side, they may still lead to some minor travel delays, including flight delays and cancelations.
Later in the week and through the start of March, with the cold air still in place and storms finally returning rain and mountain snow to California, the path could be laid for one or more disruptive snowstorms to travel from the Rockies to the Plains to the East Coast.
AccuWeather.com meteorologists will continue to monitor the potential for such snowstorms and will give more information as it becomes available.