Thundersnow
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If you were at or near Harvard at about 2:00 PM today, you were
undoubtedly aware of heavy snowfall. You may also have seen a bright
flash followed by a loud bang. At 2:10 PM the National Weather Service
advised that thundersnow is possible this afternoon. Nothing quite like post-mortem prognostication.
Thunder and lightning during a snowstorm, while rare, obviously can
occur. The makings of any thunderstorm is cold air at altitude lying
over warm moist air at ground level. While it is easy to see how this
can occur over a lake on a hot summer’s day, extreme cold air at
altitude can provide adequate temperature contrast in winter.
Thundersnow is more likely to be associated with large snowstorms than
small. It is also more likely near water. Very rapid heavy snowfall
usually accompanies thundersnow.
The question of early closing of the libraries may well be moot. This
thing will probably dump a bunch of snow and be over before we can
clear out.
Update [2:49 PM] : In fact, the predicted mixing to rain appears to occurring.
Stay tuned if you’re interested in convection and charge separation.
