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Winter 2011

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

February 8, 2011

Thundersnow

Only rarely will a snowstorm rumble

The heavy, icy snow that hit the Washington area on Jan. 26 was accompanied by muffled thunder claps
-- an unusual soundtrack for a winter storm.

Thunder and lightning are normally associated with warm-weather storms:

The January 26, 2011, thundersnow storm.

The thundersnow storm of Jan. 26.

Hot, moist air rises quickly and cools at high altitudes, forming rain, ice pellets and ice crystals. The heavier rain and larger ice pellets fall, but the tiny ice crystals rise on the strong updrafts. When crystals and pellets collide, electrons are stripped away from the crystals and rapidly form positively
and negatively charged layers in the clouds. Lightning flashes neutralize the charges, causing the surrounding air to violently expand and create thunder.

In winter, moist air starts off colder, so
in a storm it doesn't rise as quickly or generate much of a charge.

But an extra-strong low-pressure area
at a high altitude can suck up enough
air to keep ice crystals (in the form of snow) aloft, allowing clouds to build up enough static to pop.

The boom of the thunder, however, is damped by the snow-filled sky.

SOURCES: Walter A. Petersen, NASA; American Meteorological Society

Anatomy of a thundersnow storm.

A cross-section through a thundersnow storm.