Tuesday, January 17, 2012

Freezing Rain Possible Saturday Morning

It appears as though the least welcomed type of winter weather could make an appearance in the state this weekend. A fairly strong (1028 mb) area of high pressure will build into New England Friday into Saturday, with the wind flow around this high moving in a clockwise direction. This air mass will be cold and dry, with the coldest air hugging close to the surface because of its relatively high density. The air will move freely southeast, south, and southwest, but will not be able to move west over the Appalachians. Instead of flowing up and over the mountains, the cold air will funnel down the east side of the mountain chain. This process is called "cold air damming", or "the wedge effect", and allows the shallow cold air associated with strong high pressure to spill as far south as Georgia along the east side of the Appalachians. Because the sub-freezing air will be so shallow, rain will fall in liquid form, but will freeze on contact to all objects at the surface. While the rain should be light during the time of sub-freezing surface temperatures, even a minor accretion of ice will cause problems. The graphic I created indicates where I think icing will be possible, and highlights where I think the greatest risk will exist. I'll continue to monitor the latest model data, and will have another update here tomorrow. -Zach