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Here's the basic explanation for this image offered by NASA on November 30, 2004 (go to their webpage
for links to much more information about lake effect snow).
Also see this page
for some very nice animations and descriptions assembled by the National Center for Atmospheric Research at the University of Colorado-Boulder
(http://www.ucar.edu)
Those strange clouds stretching out from the Great Lakes are caused
by cold air moving over the relatively warm water (at least a
lot warmer than the air). This results in rising bands of moistened,
warmed air that drop "lake-effect snow" alternating
with clear bands of falling cold air. During winter, such bands
can create hundreds of centimeters of snow more than upwind areas
only a hundred kilometers away. Just ask the folks that live on
the Keweenaw Peninsula
on the southshore of Lake Superior or the folks in Buffalo, New
York. Here in Duluth, our "Mega Storm" from Halloween
night on 1991 that dumped more than 3 feet on us in a couple of
days was in part due to lake effect snow. This image from November
30, 2004 was caused by a cold northwesterly wind over Lakes Superior
and Michigan and was taken with NASA's SeaWiFS satellite.
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