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Arctic air plunging into the Pittsburgh region thanks to polar vortex

PITTSBURGH — January was a mild one for Pittsburgh, with the monthly temperature almost two degrees above average. Snowfall finished a half an inch above average.

Back in mid-January, we told you how the polar vortex was weakening and that a stratospheric warming event was taking place. Remember, the polar vortex is a region of low pressure and very cold air that’s swirling in the polar regions, and it’s always there. Sometimes the polar vortex can weaken or be disrupted, which can lead to very cold air spilling into the eastern U.S.

The polar vortex split, as forecast, and signs are that a lobe will be over Russia and Greenland, with the dominant lobe over Greenland starting the week of Feb. 8. You can see that in the image.

Sudden stratospheric warming, (or SSW), is when atmospheric waves that are associated with weather systems are able to reach into the stratosphere. This can disrupt the polar vortex.

Looking at the high-pressure and low-pressure anomalies at 500 millibars in the atmosphere, which is roughly 18,000 feet, there’s forecast to be high pressure over Greenland and the Gulf of Alaska. This blocking can lead to more disruptions in the polar vortex and more periods of cold for our part of the country.

A chunk of arctic air should be able to “break off” and invade our area starting around Feb. 7 or Feb. 8.

The first half of February looks to bring below-average temperatures. Average highs are in the upper 30s and average lows are in the low 20s this time of year. The Climate Prediction Center is on board with colder weather for our area, too.

Rain and snow are also forecast through the first half of the month. Once the arctic air invades around Feb. 7 or Feb. 8, it may stick around for many days. The air will be some of the coldest we have had since 2019. In fact, looking at Feb. 8 specifically, forecast lows are to be the coldest since Jan. 31, 2019 when the low temperature dipped to -5 degrees in Pittsburgh. In case you’re curious, that’s also the last time the city fell below zero.