The Impact of Ice Cover on Two Lake-Effect Snow Events in the Eastern Great Lakes Region

General meteorological intuition suggests that the development of lake-effect systems is inhibited when lakes are extensively ice covered. A recent investigation using visible satellite imagery found several events where lake-effect clouds developed over regions of the Great Lakes having ice concentrations exceeding 80%. Recent observations have shown that significant lake-effect snowstorms can occur with widespread ice coverage; however the impact of ice cover on these events has not been examined despite its noted importance to winter weather forecasting in the Great Lakes region.

The study to be presented examined two significant lake-effect snow events which occurred downwind of Lakes Erie and Ontario on 12-14 February 2003 and 28-31 January 2004. For each event, snowfall totals of more than 30 cm and 200 cm occurred along the shores of Lake Erie and Ontario, respectively, during time periods when Lake Erie had widespread ice cover and Lake Ontario was predominantly ice-free. The investigation utilized Great Lakes ice charts, MODIS satellite imagery, radar data, soundings, and surface observations. The mesoscale evolution in snow band duration, intensity, and structure was similar for both events in the vicinity of Lakes Erie and Ontario. While an intense shoreline snow band occurred over Lake Ontario for the full duration of each event, the structure and intensity of the lake-effect snow bands varied in the vicinity of Lake Erie. An assessment of the environmental conditions showed estimated surface total heat fluxes in the vicinity of Lake Ontario were approximately 300-400 Wm^-2 and only on the order of 50 Wm^-2 over Lake Erie when extensive ice cover was considered. The presented research will focus on (1) the role ice cover played in limiting the surface heat fluxes, (2) their subsequent impact on the development and strength of lake-effect mesoscale circulations near Lake Erie, and (3) a comparison of the evolution of lake-effect mesoscale systems and snowfall near Lakes Ontario and Erie.