A 30-year climatology of lake-effect snow events in Indiana, including an analysis of upstream sounding variables as Predictors

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Monday, 18 January 2010: 1:30 PM
B211 (GWCC)
Craig A. Clark, Valparaiso University, Valparaiso, IN

Using available data, an extensive climatology has been developed for the lake-effect snowfall belt in northern Indiana. Snowfall reports, as well surface and upper air analysis, were used to isolate lake-effect snowfall from synoptic events. With a minimum snowfall threshold of five cm, there are ~250 cases in the data set. While at lake-effect snowfalls exceeding 25 cm occur during most seasons, the majority of events have snowfall less than 13 cm.

Although it is difficult to distinguish between heavy and moderate events, there is a demonstrable dependence of snowfall on upstream parameters from the sounding at Green Bay, Wisconsin. The best sounding predictors are 850 hPa wind direction and low-level instability (or ΔT), with the heaviest snowfall cases typically characterized by a long fetch across Lake Michigan and moderate to strong instability. Upstream inversion strength behaves as a limiting factor, with strong inversions inhibiting snowfall. The inversion height, however, has a very weak relationship with snowfall; this is likely due to the substantial boundary layer modification resulting from flow over the lake. Other sounding parameters, including relative humidity and wind shear, have only minor relationships to snowfall.