January 20, 2010 - Winter Weather Returns

By: Mallory Brooke
By: Mallory Brooke

There’s so much weather and so little time to explain it all. We have another winter storm coming our way. Click here for the details.

Here we go everyone – a blog just for you. There’s so much weather and so little time to explain it all. This blog is a more detailed look at our forecast and also a place to delve into some of those crazy weather terms we use on-air. Feel free to comment and ask questions of your own!

Our taste of spring has come to an end in the Valley, as our next storm system approaches from the west. A lot of uncertainty lies within the storm, from precipitation type to timing to the duration of the system.

Let’s break down the weather for the next 48 hours.

Our cloudy, dreary Wednesday sets us up for our next potential winter storm, which depends so highly on surface temperatures. With Wednesday’s high temperatures barely breaking 35 degrees, we should have no problem dropping below freezing Wednesday night.

More precipitation will develop in the Lexington and Roanoke area Wednesday evening due to overrunning. Overrunning usually occurs near and north of the warm front or stationary front, which is to our south at the moment.

Warm moist air rides up and over the cool air at the surface. Water vapor condenses as it rises, forming clouds and precipitation. Overrunning is the most common process for the production of ice, specifically freezing rain. However, the northward progression of the overrunning will be limited by strong high pressure in Canada.

The southernmost areas in the Valley may see a brief period of rain and/or freezing rain as this first batch of precipitation affects the Valley overnight Wednesday.

We anticipate the main event to begin Thursday afternoon. As I previously mentioned, lots of uncertainty lies within the storm. Models are disagreeing with each other, which is not too surprising, as there are a lot of elements that come into play. Not only do we have our low pressure system to the west, but we’re also anticipating a coastal low pressure to develop during the height of the storm, and high pressure to the north placing us in a Cold Air Damming (CAD) situation. Sometimes the models just can’t handle all the excitement!

The RPM model has indicated a prolonged ice event from lunchtime Thursday through Friday morning with temperatures in the upper 20s. This is the model that you see on our “Futurecasts” during the broadcast. Over 12 hours of icing would have serious impacts to our area, especially for those commuting home Thursday evening and to work Friday morning. Another model we look at, the WRF model, has more marginal temperatures (closer to the freezing mark) with precipitation beginning around 7 p.m. Thursday and overspreading the region from south to north.

However, it keeps precipitation in the area through 5 p.m. Friday: 22 hours of icing with a changeover to snow possible. The GFS model brings the precipitation into the Valley around 4 p.m. Thursday, lasting until 10 a.m. Friday. See what I mean?

What all models agree on is the possibility of significant icing in the Valley and that we will be in a cold air damming setup over the next 48 hours. What is cold air damming and why does it form here? Read all about it tomorrow’s blog.
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