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Directional Convergence Forced by the Terrain

Maps from nationalatlas.gov now called The National Map of the U.S. Geological Survey's (USGS) National Geospatial Program

Higher elevations on both sides of the narrowing tip of Lake Superior force broad low-level convergence as winds blow toward the head of the lake from an east-northeast direction. When winds are more from the east, the hill along the north shore of Lake Superior deflects some of the air so that the air flows parallel to the hill. The difference between the direction of the deflected air and the direction of air approaching from the east results in directional convergence of the two airflows.

Directional convergence can also occur with an offshore wind direction. In this case, wind from the north to north-northeast converges with winds from an east-northeast direction from over the lake. One way to help snow to fall in Duluth would be for winds to veer with height, meaning that they turn more from the east or southeast as you go upward. The snow would then be blown back inland.