February 12th, 2012 at 12:40 am by under Uncategorized, Weather

The quick hit of snow over Hampton Roads late Saturday afternoon caused quite a stir!  A cold front charging into the region brought a squall line that started as rain and sleet, and quickly changed to snow.  Then all of a sudden, rumbles of thunder were heard and lightning seen.  So what happened?

Thundersnow is literally a thunderstorm that produces snow instead of rain.  While it is rare, it occasionally happens in Virginia, particularly with the passage of an unusually strong cold front or during a very intense snowstorm.  The most famous example of thundersnow that comes to mind is the February 2011 blizzard in Chicago.  Jim Cantore was live on The Weather Channel when the thunder occurred. 

You need just the right ingredients to get thundersnow.  Very cold air aloft and the approaching cold front caused strong vertical motion in the atmosphere.  This set-up is very similar to what occurs during a spring or summer thunderstorm.  The storm becomes convective in nature, with thunder and lightning the result.

So why don’t we see thundersnow more often?  It’s rare because the temperature profile in the atmosphere usually doesn’t support convection and snow at the same time.  Typically the lower layers of the atmosphere are quite cold with lower dew points.  This results in relatively drier air and greater stability.  Today, however, you probably noticed that the air temperature when the change to snow occurred was around 40 degrees.  The air aloft was much colder, creating the needed instability for a quick burst of heavy snow.  Some of the cold air then rushed to the surface as the front moved through.

So the wild weather in Hampton Roads continues!  While the wind will kick up a bit and it will be cold to finish the weekend, a lot of sunshine is expected.

See you on the air,
Mike Goldberg

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