Arctic air flowing across relatively warmer river produced a "river-enhanced" snow band downwind (southeast) of the lake on Monday morning, impacting counties from Buffalo southeast through La Crosse and Vernon. The temperature profile favored clouds parallel to the wind direction (northwest to southeast) across the entire region (called "cloud streets"). Additionally, since the orientation of the Mississippi River from Pepin to La Crosse is also northwest to southeast, the small amount of heating from the river below (even when ice covered!) enhanced the vigor of the cloud street along and downstream of the river enough to produce snow. The 3 mile wide snow band did waver a bit and reports of around 1/2 inch of snow were reported from it. However, visibilities lowered to 1/4 mile in the band at times! This band was most intense Monday morning, but lingered into Tuesday as the winds remained from the northwest.
A special thanks to the DNR for providing ice cover information for Lake Pepin.
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