Michael A. Fowle, National Weather Service; Xiaoqing Wu, Department of Geological and Atmospheric Sciences, Iowa State University


In this study, the 23-24 March 2016 snow event across west central Wisconsin, south central Minnesota, tapering off into northwest Iowa and extreme southeast South Dakota was analyzed to better understand sharp gradient snow events. The focus of this study was to understand why this snow event occurred and what contributed to the sharp contrast in snow accumulations in such a densely populated area of the Minneapolis/St. Paul region. Analyses confirm that the warm, moist air from the south and east at low levels combined with the cold, dry air from the north and west at the upper levels enhanced lift, moisture and instability, constituting to the impressive snowfall gradient across the Upper Midwest. Additionally, the study looked to analyze both the model outputs from the North American Mesoscale and Global Forecasting System and compare atmospheric variables to what was actually observed as the snow event began on the 23 March at 12 UTC at certain locations affected by the snow band. Locations that saw the most snowfall also saw the highest values of omega, moisture, and instability, which agreed with what was hypothesized. Both models handled the event similarly, forecasting snowfall in locations within the dry slot best, but showed uncertainty within locations in the snow gradient. The greatest model disagreement in wind direction came from forecasts at 700 hPa.

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Samuel L. Gabrielli


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