Expert: Dave Dombek - 2/21/2005

Question
OK, but my other main concern is why is there a gap in Virginia?

The whole state of Virginia is always skipped. Almost, all the midatlantic states are effected by this instability hence, creating snow.
I guess you're going to say it is due to the drier air downward the Appalachian mountains.

If you're saying it's instability, than why is it almost always that typical pattern, and why is there instability being created there.

Thank You.

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Followup To
Question -
Please go to this website to see my question;

http://www.angelfire.com/clone/alastrian/accuweather.html

Thank You very much.

Answer -
Alastrian,
The snow pattern you saw on that radar map was mostly due to instability, i.e., very cold air aloft, and less cold or milder air near the surface. It is the same process that causes showers and thunderstorms to form on unstable days in the spring and summer. The snow was enhanced downwind of the Great Lakes and in the upslope areas of the Appalachian Mountains. However, the main driving mechanism for the snow showers that day was instability
I hope this answered your question.

Sincerely,

Dave Dombek
Expert Senior Meteorologist
AccuWeather.com

Answer
Alastrian,
I believe there are two main reasons Virginia did not get much snow that day. (1) The general surface wind flow pattern was northwesterly. That means the air downslopes coming up and over the Appalachian Mountains. When that happens, the air tends to dry out and snow (or other forms of precip) falls apart. The mountains in western Virginia and West Virginia are higher than they are in western Maryland, Pennsylvania, and northwestern New Jersey. As a result, the downsloping effect of the air coming up and over the mountains is greater in Virginia than it is farther north, and so more of the snow showers disspipate coming over the mountains. (2)  The air aloft was slightly colder the farther north you go that day. That means that the atmospheric instability was greater in those areas than it was in Viriginia.
I hope this answered your question.

Sincerely,

Dave Dombek
Expert Senior Meteorologist
AccuWeather.com