Tuesday, January 25, 2011

Winter Storm Watch in VA for Wednesday

A Winter Storm Watch is in effect for the approaching storm system from the south for southwest, west and north-central Virginia, including the cities of Charlottesville and Fredericksburg. As of this update, the rest of central Virginia is not included in the watch for Wednesday.

The low pressure system that will produce rain and snow in the Commonwealth is currently overspreading rain through the Southeast U.S. Here's a breakdown of the precipitation, including surface temperatures. Green is rain, pink is wet snow, and blue/white is snow. This shows rain moving into central Virginia around midnight, but I think it will arrive a little sooner, closer to 9 p.m. in southern Virginia.

The precipitation will all fall as rain initially in our area, but notice that the pinks (wet snow) appear closer to sunrise in the areas included in the Winter Storm Watch:

Rain will continue through the morning in most of central Virginia, with surface temperatures above freezing. At Noon, the Watch area is still receiving a wet snow that is probably only accumulating on grass and other elevated surfaces because surface temperatures may be just above freezing.

By sunset, colder air will wrap around the low pressure system (to the east of Virginia by this time, offshore) and allow rain to change over to snow from west to east. However, notice the temperature remains above freezing in most of the area, keeping accumulations to the grass and other elevated objects.

Snow will end from west to east before sunrise Thursday. Much of the snow that falls Wednesday night, even though it may be heavy at times, will be melting as it hits the ground because of surface temperatures remaining slightly above 32 degrees.

Those bursts of heavy snow may occur Wednesday night because of the upper vorticity max, shown in the image below, passing directly over Virginia. This could lead to bursts of heavy, wet snowfall.

Despite these bursts, the wet snow will still be falling into surface temperatures just above freezing, resulting in some of the snow melting as it lands. Still, here is an estimate of measurable snow accumulation by early Thursday morning:

By Thursday morning, temperatures should dip below freezing, which could lead to freezing of the wetness on the roads from the rain and snow. I expect there to be some icy spots developing around sunrise Thursday, which could impact your commute with slick and hazardous conditions. We'll be providing updates on any threats to travel. Stay with CBS 6, we'll keep you ahead of the storm.

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