The Duluth-Superior vicinity is reminded almost daily of the presence of Lake Superior and its role dictating the local climate. Modification of the planetary boundary layer by the lake is manifested in a number of different ways ranging from the formation of dense fog and lake breeze fronts in the summer, to lake effect snows and land breeze fronts in the winter.
The present study concerns wintertime case which features a lake enhanced snow event that occurred mid-morning on the eighteenth of December 1996. The case consisted of a back bent frontal zone intensified by the localized planetary boundary layer circulations induced by Lake Superior. This front propagated southward through northeastern Minnesota into northwestern Wisconsin, intensifying after superpositioning with the coastal front that developed along the south shore. The positive resonant response resulted in an unexpected narrow band of snow showers with two inches recorded as far as Hickley, MN 110 km southwest of the Lake.
Numerical sensitivity studies were conducted to establish an understanding of how the sensible and latent heat flux modulated the intensity of the frontal circulation and precipitation rate. Freezing all of Lake Superior revealed that the large scale frontal zone would still be there with or without the Lake. The intensity of the frontal
circulation and snowfall, however, was significantly less with Lake Superior simulated to be frozen. Other sensitivity tests effected the solution minimally. These tests included smoothing the topography and equilibrating the land/lake frictional differential to land friction. The tests will be discussed in greater detail at the oral presentation