Mild, quiet January so far, but look for a shift to winter in about 10 days

Weather

COLUMBUS (WCMH) –The current winter has produced about as much snow in Columbus (10.4 inches) as Columbus experienced all of last winter (11.7 inches).

The present winter started off chillier than last year, averaging 1.1 degrees above normal in December 2020, but still three degrees colder than December 2019. However, January 2021 has been relatively mild and snowless, more than 5 degrees above normal in Columbus.

The current weather pattern in early 2021 features a split jet stream flow that has kept winter storms well south of Ohio for the past two weeks, and arctic air locked up in the north.

Yet consistent indications in the long-range models point to true winter in the eastern U.S. in the second half of January, though not frigid. The signals are based on a recent “heat wave” in the stratosphere, referred to as a sudden stratospheric warming.

The dramatic high-altitude warmth usually nudges the polar vortex away from the North Pole, sometimes splitting the center of the whirlpool and leading to a southward plunge of bitterly cold air into central Canada or Siberia.

This allows at least brief incursions of cold air into the eastern U.S. beginning around Jan. 15, but a lack of frigid air in Canada will limit the degree of chill reaching the Ohio Valley. A stronger push of arctic air could occur after Jan. 25, depending on whether the snowpack builds over southern Canada and the northern U.S., which refrigerates cold air masses.

The polar vortex, the coldest air in the Northern Hemisphere, is centered about 18 miles above Earth’s surface. The gelid air is normally wound tightly around the North Pole. A slowing of the high-altitude winds creates a slower, wavier jet stream, unlocking pent-up bitterly cold air masses that begin to slide away from the Far North.

About every other winter, an upward surge of energy forms deeper waves in the atmosphere that work down to the polar jet stream, and a lobe of the frigid pool sags slowly south. The last event occurred at the end of January 2019, bringing a short-lived arctic blast to the Midwest and East, a few weeks after a sudden stratospheric warming.

Exactly where the polar vortex descends–Siberia or eastern Canada–usually determines where the coldest air moves, either eastern North America or Central Europe, often accompanied by snow on the margin.

NOAA/Climate Prediction Center

In addition, phasing of a cyclical pattern of tropical rainfall and atmospheric circulation potentially amplifies the polar jet stream, favoring more than one surge of arctic air. This is the result of a blocking formation in the North Atlantic that holds in the chill.

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