Friday, November 21, 2008

Wrapping Up Fronts

There is another type of cold front sometimes mentioned during the weather report -- and that is the "back door" cold front.

It's no different than a typical cold front except it moves in from the east or northeast, where as most cold fronts approach from the north or northwest.

It can happen anywhere, but is most common on a large scale in the New England states.

On a smaller scale, we get a lot of back door cold fronts along the eastern side of the mountains here in Colorado.

Cold air from Nebraska will pool and spill down the South Platte River Valley and into the Denver/Front Range area.

We had that happen this week in fact!

When a back door cold front moves into the New England states, often the cold air hits the Appalachian Mountains and can't go any further.

This is because cold air is heavy and dense, and it can't rise up and over high barriers like a mountain range.

We call this cold air damming.

So the cold front stalls along the mountains (cold air damming) and will actually become a stationary front since it stops moving.

Back door cold fronts combined with the terrain barrier make for tricky forecasts -- because you just don't know how much "umph" the front will have to make it up and over the mountain barrier.

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