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Page 14

By Mark Bloomer

Forecaster

NWS Caribou, Maine


Showers of sleet were falling across much of northern Maine during the cold, grey Sunday afternoon of February 23rd.  Temperatures were within a few degrees of 20 and a chilly northeast wind was blowing.  Late in the afternoon thunder began rumbling along the southwestern horizon, and within a few moments heavy showers of sleet were being accompanied by strong bolts of lightning and crackling thunder.  Three teenagers were hit by a lightning strike on the Caribou golf course as they were carrying their sled up a hill.


Afternoon thunderstorms are commonly associated with warm spring or summer afternoons following some heating from the sun.  When thunderstorms appeared on a cold, gray February afternoon during a winter storm it seemed very unusual, and especially unlikely that anyone should get hit by a lightning strike.  How rare are winter thunderstorms?  How do they differ from summer thunderstorms?


The basic mechanism in the creation of a thunderstorm is warm moist air from the low levels of the atmosphere buoyantly rising into colder air aloft.  During spring and summer thunderstorms, sunshine will warm the ground which in turn warms the air near the earths surface.  If the air aloft is much cooler than the air near the ground, the surface air will rise and moisture in the air will condense into clouds. Towering Clouds high in the atmosphere can produce rain and hail, and processes involving hail descending through water droplets may cause electrical charges to separate resulting in lightning.


Producing a thunderstorm in winter is more difficult, and a bit more complex than producing one during the summer season.   On February 23rd a strong storm system lifting through northern New England pulled a layer

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Winter Thunderstorms

Rare thunderstorm in February...How did it happen?