Thanksgiving 1996 Lake Effect Snow in the Lake Champlain Valley

Lake effect snow occurs during the cold season in the Lake Champlain Valley situated between the Adirondack Mountains of New York and Green Mountains of Vermont. Lake Champlain is located in a north-south oriented valley at an altitude of 30 meters above mean sea level. The lake lies between the Adirondack Mountains to the west, which rise up to an elevation of 1600 m, and the Green Mountains to the east, which rise to 1340 m. One of the key mechanisms for terrain forcing for vertical motion in addition to lake effect snow band formation is surface convergence as a northerly flow of cold air flows southward down the valley and across the lake as the valley narrows between the mountain ranges that surround it.

On 27 November 1996 a cold air mass moved over the relatively warm waters of the lake causing a persistent lake effect snow band from which 33 cm of snow fell in Cornwall, VT, which still ranks as one of the most extreme cases of lake effect snow downwind of Lake Champlain. We use the Weather Research and Forecast model to simulate this event and to determine if it is possible to reproduce this event, including terrain-induced forcing for lake-effect snow formation. We use varied grid resolutions, initial and boundary conditions, and model physic packages to produce guidance with sufficient detail to alert operational forecasters to the potential of a high impact lake effect snow event.

The ultimate goal of this research is to identify the key model resolution and physics requirements needed to operationally produce a realistic lake-effect snow forecast for the Champlain Valley. It is argued that the predictability of the magnitude of these events will increase as operational models grid spacing decreases.