Soccer Dad

"Thundersnow"

A little before 10 last night we heard some very loud thunder, not exactly standard for Janary. A little later 2 of our sons came upstairs to tell us that there was thunder, lightning and ... snow!

That prompted an e-mail to the Maryland Weather Blog:

"Last night about 10 PM two of our sons came upstairs excitedly telling us that there was a "thunder snow" going on. We were of course aware of the thunder as it had been quite loud. And it was unusual to hear at this time of the year. But the idea of there being a thunder storm in which it was snowing is not something I ever remember.

"How (in)frequent are such occurrences? Since I suspect that the Weather service doesn't actually track "thundersnows" let me ask what unique conditions (if any) must occur for there to be a "thundersnow."

Well my assumption that they didn't keep track of such events was wrong. The Maryland Weather Blog answered both my questions:

Obviously, thundersnow is very rare. Meteorologist David Schultz has studied the phenomenon and estimates that only seven in 10,000 recorded thunderstorms produce snow. But there are a lot of thunderstorms, and a lot of snowstorms. So there are plenty of opportunities for thunderstorms to produce snow, or snowstorms to produce thunder. I can recall several severe winter storms in Baltimore since I moved here 25 years ago that have been spiked by claps of snow-muffled thunder.
...
I called the NWS forecast office in Sterling, Va. and asked meteorologist Brian Guyer what happened last night.

He said lightning (and therefore thunder) requires strong vertical motion in the clouds. That motion strips electrons from water and ice particles and creates an electrical difference between the ground (positive) and the base of the clouds (negative). When that difference is strong enough, a spark - a lightning bolt - jumps the gap.

In a severe winter storm, that electrical gap is created by the strong vertical motion of falling snow and ice. That's true "thundersnow."

Well thanks Mr. Weatherblogger! Now I know.

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