Philadelphia (WPVI) -- Nearly every winter in the mid-Atlantic we encounter a weather situation called Cold Weather Damming. It is a challenge for meteorologists and it can result in an extended period of snow and frozen precipitation.
The set-up for cold air damming starts with high pressure establishing itself over New England.
Clockwise circulation around that high pulls in cold air at the surface. Often, at the same time, a storm moving moisture up from the south pushes in warm air higher in the atmosphere.
The warm air can't overtake the colder air because the mountains act like a dam. That cold air is wedged east of the mountains. Because the air is cold and dense, it hugs the ground, maintains its position.
As the storm's moisture moves in we get a prolonged period of front end snow and a wintry mix.
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