I’m Dreaming of an “Ice” Christmas

Brian Neudorff @ 11:39 am December 22nd, 2009 · No Comments

(Note: The title “ICE” Christmas was catchy but I don’t nor do the News 8 weather Team expect a major ice storm Christmas morning)

At this point, to follow up Bob’s and Scott’s posts from the past few days, it’s safe to say that Christmas will not be white. It will be wet with rain but our focus is on Christmas morning. Across the Mid-Atlantic we are setting up a cold air damming situation along the Appalachians and Mid-Atlantic. This can and may cause some slick and icy travel Christmas morning.

What is cold air damming? If you get an area of high pressure located over eastern Canada and northern New England the anticyclonic flow will bring cold air down out of Canada and along the eastern side of the Appalachian Mountains. Because cold air is more dense than warmer air it will sink and fill into the valleys and can extend from eastern and central New York down into North Carolina or even Georgia.

With the next approaching storm we will see warm air advect or advance into western New York and through the Appalachians and Mid-Atlantic. As I mentioned above, cold air is more dense and heavier than warm air so the warm moist layer of air will go up and over the cold sub freezing layer at the surface. Because the warm layer is well above the surface, it won’t snow, but with cold sub freezing air at the surface, we can get sleet or freezing rain.

The way things look right now, for a brief period during Christmas morning, surface temperatures will be at or just below freezing and shallow allowing some of the rain to come down as freezing rain. Looking at the cross section forecasts for Rochester from Coolwx.com of the NAM and GFS models, it doesn’t appear that much freezing rain will fall. We still have a couple of days left to fine tune things but if you plan on traveling before Christmas the next few days look great. If your plan was Christmas morning, you may want to think about leaving Christmas Eve or waiting until any freezing rain changes over to rain.