Dust from the parka.
After a mild December, the polar vortex is expected to deliver an arctic blast to the US later this week.
“The polar jet will be pushed further south, and guess what that does? It opens the freezer door,” said FOX Weather Meteorologist Kendall Smith. “So, all that cold arctic air that’s been bottled up over Canada, right over the Arctic, is going to blast right into the Lower 48.”
According to the FOX Forecast Center, this may be the coldest air the Lower 48 has experienced so far this winter.
The cold starts late in the week in the Intermountain West and then hits the central US early next week.
Cold air will stick for a while.
How cool will it be?
Weekend temperatures could fall into the 30-50 degree range below average for this time of year for some locations.
The wind chill can approach -50 degrees in some places.
A temperature survey from the Climate Prediction Center shows below-average temperatures through Minneapolis, Kansas City, Little Rock in Arkansas, Nashville in Tennessee and Chicago through Jan. 18.
People walk in the snow on the Brooklyn Bridge during a winter storm on January 6, 2023. Paul Martinka
Why are winters mild, and what changes them?
El Niño is partly to blame for the mild winter so far in the US.
During El Niño winters, temperatures in the northern US are typically warmer and drier than average, according to NOAA. The jet stream usually flows more west to east.
“So we were kind of lucky for a good part of December and even early January, but now it’s kind of a page turn, if you will, a complete flip of the script,” Smith said. “Because now we’re starting to see cold air that’s locked in place over Canada and over the Arctic. That will start to change.”
About two weeks ago, the Arctic experienced a small and sudden stratospheric warming.
Air in the stratosphere, the inner layer of Earth’s atmosphere about 19 miles above the surface, warmed by 55 degrees over six days, writes Amy Butler of NOAA’s Laboratory of Chemical Sciences. That slows down the polar vortex.
About every year, weather events in the lower atmosphere send strong atmospheric waves into the stratosphere, which interact with the polar vortex.
A polar vortex is a group of strong winds that surround the North Pole. A steady, steady rotation of winds keeps the arctic air locked in place.
When the wind slows down and becomes unstable, like a top, the eddies sway.
The polar vortex on the left is from January 1st and the right side is the forecast for January 14th showing cold air stretching south. NOAA Climate.gov
Stratospheric weather leads our weather by up to two weeks, according to Judah Cohen, Atmospheric Scientist from Verisk Atmospheric and Environmental.
“A polar vortex disruption called sudden stratospheric warming, where you have a very dramatic warming of the North Pole in the stratosphere, and the polar vortex then migrates south, out of where it’s normally placed in the North Pole, to the south,” said Cohen. “And cold air can then move south and then, at the surface, that will often manifest in a negative Arctic Oscillation.”
During the Great Texas Freeze in February 2021, the Arctic Oscillation was at its lowest, most negative, reading in eight years.
Nor’easters are also associated with negative Arctic oscillation phases, according to NOAA.
How long does a dangerous cold stick around?
How long the cold air remained in place, last week, remains unclear.
“However, there is still uncertainty in how the polar vortex will develop after mid-January,” Butler wrote. “Meanwhile, there are signs that even this small warming could help strengthen the possibility of cooler weather patterns in some areas over the coming weeks – stay tuned!”
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Source: thtrangdai.edu.vn/en/
