Arctic air mass means likely below-normal temperatures across eastern U.S.

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Arctic air mass means likely below-normal temperatures across eastern U.S.

In the winter season, meteorologists keep an eye on the arctic oscillation - called AO. 

The AO is a large scale mode of climate variability, also referred to as the Northern Hemisphere annular mode. The AO is a climate pattern characterized by winds circulating counterclockwise around the Arctic at about 55 degrees North latitude typically known as the polar vortex.


Currently, the AO is in a negative phase and is forecast to remain negative through at least the middle of December. 

This will likely mean temperatures across the eastern United States will average below normal.

When the AO goes into a negative phase, the polar low pressure system (also known as the polar vortex) over the Arctic is weaker, which results in weaker upper level winds (the westerlies). 

The result of the weaker westerlies is that cold, Arctic air is able to push farther south into the U.S., while the storm track also remains farther south.

The opposite is true when the AO is positive: the polar circulation is stronger, which forces cold air and storms to remain farther north. 

The Arctic Oscillation often shares phase with the North Atlantic Oscillation and its phases directly correlate with the phases of the NAO concerning implications on weather across the U.S. 

Currently, the AO is in a negative phase and is forecast to remain negative through at least the middle of December. 

This will likely mean temperatures across the eastern United States will average below normal.

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