Tuesday, January 5, 2010

Unseasonably Cold Temperatures

Unseasonably cold weather will linger through the weekend into next week as a result of the deep low pressure trough stationed over the eastern half of the U.S. The image below is a view of the upper trough looking down onto the Northern Hemisphere, showing the source region of the trough in Canada all the way into the Southeast U.S.:
This means cold air continues to plunge into the northern Plains and upper Midwest from north-central Canada. While modification of the Canadian airmass does occur as it moves southeast, it is moving over a lot of snowcover, which helps keep the air cold.
Streamlines show us how the air is moving, and you can see a stout flow from the upper Midwest over the Appalachian chain into Virginia. That means cold Canadian air is plunging into the Midwest over snowpack, over the mountains and into the Commonwealth.
Storm tracks will follow a similar path as they dive into the Plains from Canada and head eastward. Our next upper disturbance will plunge south Wednesday into the Plains, then head toward the East coast late Thursday and Friday, producing a quick light snowfall across the region. In Central Virginia, only minor snowfall accumulations are expected, generally from a dusting up to an inch as a result of limited moisture availability.