Thanks to the polar vortex, dramatic cold air could hit the United States in late January. What could happen?
What is a polar vortex? How it affects snow and ice in the United States
A polar vortex is a large region of cold air that circulates over the North Pole. If the wind is strong, the wind will be suppressed, but if the wind weakens, it may sway or stretch.
Our winter friend, the polar vortex, is scheduled to send bitterly cold air south from Canada twice more in January, once over the weekend of January 17th and again in about a week.
“The first round of cold air over the weekend and early next week will be an appetizer, with the real cold air coming in the following week,” AEM climatologist Judah Cohen said in an email to USA TODAY on Jan. 14. “I think the second wave of cold air could be more extreme.”
Another expert, Weather Trader meteorologist Ryan Maue, agreed, pointing out this week: “This is two weeks away, so the details and intensity will change, but we are poised to see a potentially historic arctic ‘polar vortex’ eruption across North America by the end of January.”
“Stretched” polar vortex
According to the National Weather Service, a polar vortex is not a storm but a large, sustained region of low pressure and frigid air high in the atmosphere above the Earth’s poles. This phenomenon exists all year round, but is stronger in the winter when polar temperatures drop, and weakens in the summer.
When the vortices are strong, cold air remains trapped above the poles.
But if the vortex weakens, stretches, or becomes disturbed, some of that unspeakably cold air can flow south into the United States, Europe, or Asia, creating the frigid air of the Arctic. That’s what’s happening in January.
Cohen said there will be one polar vortex in mid-January. Its range will return to below normal into the eastern United States.
Recently, much of North America’s cold air was cleared by a strong (but more importantly circular) polar vortex in early January, allowing calm Pacific air to flow into much of Canada and the United States. The polar vortex will briefly ease before the next stretch begins as we approach the final week of January.
At that point, Cohen said, “the expansion of the polar vortex will begin in western North America and quickly slide eastward. This will reintroduce the cold air over western Canada that we saw for most of December, then move southeast into the north-central United States and ultimately into the northeastern United States during the fourth week of January.”
What does this mean for snow and cold?
The $64,000 problem is snow, Cohen told USA TODAY. “Snow is likely to continue in the usual places, such as around the Great Lakes and in northern New England’s lake effect regions. It’s a tough call whether we’ll get a lot of snow in the big cities. I think this pattern will eventually start to snow more broadly, but that’s not clear. In the meantime, it looks like we’ll get another nuisance type of snow from the Alberta Clippers.”
According to AccuWeather, the large, rounded shape of the drop in the jet stream makes it difficult for the southern storm to quickly intensify along the Atlantic coast and become a major snowstorm.
“Most of the storms will remain weak and move quickly, moving out to sea through much of next week,” AccuWeather meteorologist Alex Sosnowski said in an online forecast. “However, even a short change could be enough to cause the southern storm to take a course further north and closer to the Atlantic coast.”
Meanwhile, temperatures in Chicago are expected to fall from near normal to 10 to 20 degrees below normal over the next one to two weeks, according to AccuWeather. The average high temperature in Chicago is near 32 degrees Fahrenheit.
In New York City, during the polar vortex, temperatures range from 5 to 10 degrees below historical averages in the low 30s.
