SYNOPTIC MECHANISMS ASSOCIATED WITH SNOWFALL INCREASES TO THE LEE OF LAKE-ERIE AND LAKE-ONTARIO

Snowfall is a cyrospheric variable that impacts nearly every sector of society. Because of its societal importance, snowfall is a logical va riable to be used as an indicator of potential global environmental ch ange. This study investigates the mechanisms responsible for large obs erved snowfall increases across the eastern Great Lakes region of the USA. Results indicate that mean snowfall amounts across sections of we stern New York and north-western Pennsylvania have increased by up to 100 cm over the 60-year period encompassing the snowfall seasons 1930- 1931 through to 1989-1990. A synoptic climatological approach is utili zed to identify consistent synoptic-scale atmospheric patterns respons ible for snowfall across the region. Nine synoptic types are identifie d as producing significant snowfall in the study area; five with synop tic characteristics indicative of lake-effect snowfall and four eviden cing characteristics of snowfall associated with cyclonic influence. A n examination of the seasonal frequency of the nine synoptic types ind icates a substantial increase in the frequency of the five lake-effect synoptic types and a long-term decrease in the numbers of cyclone syn optic types over the period 1950-1951 through to 1981-1982. Informatio n concerning trends in the frequency and the intensity of each of the nine snowfall-producing synoptic types was combined to produce a model led snowfall change due to frequency and intensity variations over the period. Trends in the frequency and intensity of the synoptic pattern s associated with lake-effect snowfall explain the majority of the obs erved snowfall increase across the region. Variations in the synoptic types associated with cyclonically induced snowfall are shown to be un important to snowfall changes across the eastern Great Lakes area. Pos sible reasons for increases in the frequency and the intensity of the lake-effect synoptic types are discussed.