Polar Vortex: It’s B…A…A..A…C…K!!

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The polar vortex is back, so expect some cold temperatures. Image courtesy of weather.gov

The polar vortex is back, so expect some cold temperatures. Image courtesy of weather.gov

After a slight pause in its domination of weather over the United States to meander farther north and west, the polar vortex has re-established a position over eastern Canada, and will cause a serious chill in the eastern U.S. for the next week.

After that, there are indications in some of the computer models that a new weather pattern will be established.

Implications of the polar vortex’s position go beyond cold weather in New York and Chicago – all the way down to Florida in the eastern U.S.

The California Drought

The new polar vortex position is contributing to the historic drought in California. The jet stream, which surrounds the polar vortex in middle latitudes, typically establishes a pattern with four or five troughs (dips) around the globe.

At 40 degrees latitude, the Earth is approximately 18,000 miles around, so a typical wavelength (the distance from one trough to the next) is about 4,000 miles. Between each of the troughs is a ridge (crest).

So, if there is a trough in the eastern United States, there tends to be an accompanying ridge near the west coast. Under a ridge, conditions are normally warm and dry, and this is the case now in California.

Polar Vortex Returns

The combination of the polar vortex taking up a position abnormally far to the south, and the pronounced ridge in the west, creates a northwest flow in the jet stream over central Canada. This flow opens the floodgates for cold air to spill directly from the Arctic into the United States.

This means another round of near-record-cold temperatures is in store for the midwest and northeast, from Canada to the southern U.S. Cold weather will reach as far south as Florida, but overall, the cold will not be as severe as the previous outbreak.

Can the Polar Vortex Stay There Forever?

Theoretically, yes, the polar vortex could remain; weather patterns seem to have considerable persistence. But like a house guest who overstays his welcome, the polar vortex encounters pressures to leave. For one thing, summer will come, and the patterns will be different because of the reduced differential heating between equator and pole.

For another, the vortex averages a position much farther north, and this long-term average is not likely to change. In fact, there are indications that a major change in the overall jet stream flow will occur in the next few weeks.

Winter Weather: What’s Next?

Most computer models suggest that the polar vortex will loosen its grip on the eastern United States by migrating back north and changing its orientation. Currently it is elongated north-south, allowing the flow of cold air from Canada into the United States; the forecast calls for a more east-west orientation, bringing westerly winds over much of the northern United States. But don’t put away those winter clothes just yet; like that unwanted house guest, the polar vortex could return at any time.

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