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Dynamic/Synoptic Analysis - Background of LES
November 9-14, 1996 in the Great Lakes

1a. Background:

The Greater Cleveland area (Ohio) is the largest population center that is routinely impacted by heavy lake-effect snowfall (LES) within the Great Lakes region. The National Weather Service Forecast office (CLE NWSFO) is located at Cleveland Hopkins airport some 12 miles to the southwest of the downtown center. Hopkins receives about 50" of snow annually of which about 40% can be attributed to LES from Lake Erie. Some 35 miles due east of CLE NWSFO, Chardon - known as the snow capital of northeast Ohio receives over 100" annually - the majority as a result of LES.

Greater Cleveland has two snowbelts; a primary snowbelt running from eastern Cuyahoga (Ki'- ya - ho - ga) county through Geauga (Jee - aw' - ga), Lake, and Ashtabula counties in extreme northeast Ohio, and a secondary snowbelt which runs south of the city from southern Cuyahoga east and south to Medina, Summit, Portage, and northern Trumbull counties. The snowbelts are so named because of their proximity to the lake, their higher elevation relative to the lake surface, and their orientation to the lake with respect to common wind directions observed during cold air outbreaks.

[Image: Great Lakes Snowfall (23K)]

LES occurs most frequently in late fall and early winter when polar or arctic air flows over the relatively warm waters of the lake. There are great amounts of heat and moisture that "flux" into the lower air stream induced by the sharp gradient between the cold/dry air and the water surface; additionally, the cold air over warm water destabilizes the air column by creating steep temperature lapse rates in the lower atmosphere. This unstable and moisture laden lower level airmass starts to rise and form cumulus, stratocumulus, and even cumulonimbus clouds which produce the snowfall downwind of the lakes.

The snowfall increases on land due to higher elevations (i.e. the airmass is forced to rise up the sloping terrain) and the change in the frictional elements of water and land (i.e. land is rougher) which slows the flow and "bends" it slightly to the left of the overwater trajectories - the result is convergence of air along the lakeshore.

The convergence or piling up of air must be compensated in the atmospheric fluid, thus rising air is found above the convergence zone - this enhances the lift of the already unstable air parcels and produces greater snowfall.

Terms for using data resources. CD-ROM available.
Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.