Lake effect snowfalls are one of the main extreme events across the Great Lakes Basin. This type of extreme event creates sizable economic and social damage, including human fatalities and injuries, destroying vegetation, knocking out power, transportation difficulties, and property loss. Observational data suggests that lake effect regions experienced an increase in total snowfall during the 20th century. It is likely that future climate change, related to rising concentrations of greenhouse gases, will result in changes in the frequency and intensity of heavy lake effect snowstorms. Temperatures would reduce the lake ice cover and increase lake evaporation and this in return would intensify the snowstorms. However, fewer cold-air outbreaks in a warmer climate would tend to mitigate lake-effect storms. There is an important role for regional climate models to predict the future trend of heavy lake-effect snowfall. In this research, we applied a regional climate model (RegCM4) coupled with an interactive lake model to capture heavy lake effect snowfall in the Great Lakes region. We ran the model at 20-km grid spacing for 26 years (1977-2002) and compared the results with observations. In general, the model produced reasonable snowfall amounts and snowfall patterns, although usually underestimated the largest events. Based on our results, Lakes Superior and Ontario show the most frequent heavy lake-effect snowfall days. Also, the most frequent heavy snowfall events in all the Great Lakes occur on January. The model realistically simulates the observed interannual variability of lake ice, which is critical considering the response of the lake effect snowfall to the amount of exposed lake surface. We conducted several case experiments to investigate the response of the snowfall to the totally iced-over lakes. The results show that the amount of ice cover strongly affected the snowfall amounts on downstream of the lakes, as well as many atmospheric variables including temperature, wind speed, precipitable water, clouds, and vertical motion. In our experiment with 100% ice concentration imposed on one or all of the Great Lakes, the lake-effect snow mechanism weakens in general and there is no chance for the lake-effect snowstorms to be occurred. The result shows that while the sea level pressure is increasing over the lakes, the lower tropospheric winds are weakening over the lakes and on downstream of them. The result demonstrates that Lakes Superior and Huron have the widespread influence on heavy snowfall in the basin compare to the other lakes. Also, the response of some variables to the ice covered lakes is strongly related to the size and location of the lakes. For example, the positive sea level pressure anomaly on downstream of lakes Superior, Huron, and Michigan is roughly twice of that on downstream of the lakes Ontario and Erie. 011-->