Snowfall results from both passing cyclonic storms and lake-effect clouds, but the snow that falls in most of the eastern half of the Lower Peninsula and the southern third of the Upper Peninsula is primarily cyclonic and indicates what would generally prevail across the state if there were no lake-effect. In other words, the relatively low annual snowfall of 50 to 60 inches in the northeastern Lower Peninsula and southern Upper Peninsula would be typical of all the northern areas if Lakes Superior and Michigan did not contribute to local snowfall. Thus, the annual total of 180 inches on the Keweenaw Peninsula, the highest average statewide may be as much as two-thirds lake-effect snow, and the snowfall in Otsego and Antrim Counties in the Lower Peninsula may be at least 50 percent lake-effect.
    The greatest seasonal snowfall totals are found in northern lee-shore areas over higher terrain-the so-called snow-belt regions. The contribution of the lake-effect to total annual snowfall decreases southward through the western Lower Peninsula until it contributes less than half of the total in Berrien and Van Buren Counties. The annual snowfall decreases southward through all the Lower Peninsula because the percentage of winter precipitation that falls as rain is greater in the southern counties. Lake-effect snow also falls less often in the snow belt of the southwestern Lower Peninsula than in the north because there are fewer days when the atmosphere is sufficiently colder than the water of Lake Michigan to generate the lake-effect.

Climatic "lake effects" stem from the water surface that the lakes expose to the atmosphere and from the contrasting physical properties of land and water. The lake-vs-land contrasts can result in pronounced surface temperature gradients at shorelines. The most widely known climatic influence of the Great Lakes involves lake effect snowfall. However, the lakes influence many other aspects of climate, including air temperature, summer precipitation, cloud cover, and local winds.
    As cold arctic air masses sweep over the lakes, they warm from below and become saturated. The unstable, saturated air rises and may produce heavy showers of "lake effect snow". As this air moves over the lee shores of the lakes, additional lifting is provided by low hills and by convergence as the air slows down over the rougher terrain. Lake effect snowfall can account for 30% to 60% of the total snowfall at some locations immediately to the lee of the lakes.
    The map below shows average snowfall for the Great Lakes region, for the years 1951-1980. The major lake effect snowbelts are clearly shown by the darker shaded areas. The data illustrate that these lake effect belts are primarily located east or south of the Great Lakes.


Source: Norton, D.C. and S.J. Bolsenga. 1993. Spatiotemporal trends in lake effect and continental snowfall in the Laurentian Great Lakes, 1951-1980. J. Climate 6:1943-1956.

One of the major mechanisms whereby air is lifted, and lake effect precipitation is formed, is called "convergence uplift". This type of lifting occurs as air moving across the smooth water body (lake) encounters the rougher land mass. The air then "piles up" on the lee shore zone, and is forced to rise. This rising action sparks much of the lake effect snow near the lee shores of the Great Lakes. The diagram below shows how convergence uplift occurs, and also illustrates that the opposite situation on the windward shores (e.g., Wisconsin) inhibits lake effect snow there.

Source: Unknown


Parts of the text on this page have been modified from L.M. Sommers' book entitled, "Michigan: A Geography".

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