Why an unusual phenomenon will cause a frigid December in the U.S.Archive Today
A sudden stratospheric warming could soon disturb the polar vortex. Why that will cause frigid air to spill from the North Pole to North America.
December might be extra chilly this year across parts of the United States this year because of a weather phenomenon unfolding miles above the North Pole.
It’s called sudden stratospheric warming and happens once every other winter on average, but very rarely in November. Despite the name, its occurrence does not imply there will be any sudden warming where people live. In fact, it’s almost the opposite.
A rapid warming and weakening of winds in the stratosphere can disturb the polar vortex, a ring of frigid, stormy air that typically sits high above the North Pole.
Impacts can cascade downward through the atmosphere, sometimes causing very cold air to spill southward toward more populated areas, as the polar vortex becomes displaced or elongated.
This process can take weeks to unfold, but long-range forecasts favor below-average temperatures across parts of 35 states from late November into December, particularly after Thanksgiving.
How and why it happens
Sudden stratospheric warming events are natural phenomena, happening once every other winter on average.
But major events in November are very uncommon, with only one occurring since the 1950s — and the one predicted this November may become the earliest on record. They more typically occur in January and February and not in November or December. That’s because the polar vortex is still in its formative stages during late fall and early winter, making it less susceptible to warming events.
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