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

Abstract

Snowfall is a cyrospheric variable that impacts nearly every sector of society. Because of its societal importance, snowfall is a logical variable to be used as an indicator of potential global environmental change. This study investigates the mechanisms responsible for large observed snowfall increases across the eastern Great Lakes region of the USA. Results indicate that mean snowfall amounts across sections of western 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 utilized to identify consistent synoptic-scale atmospheric patterns responsible for snowfall across the region. Nine synoptic types are identified as producing significan t snowfall in the study area; five with synoptic characteristics indicative of lake-effect snowfall and four evidencing characteristics of snowfall associated with cyclonic influence. An examination of the seasonal frequency of the nine synoptic types indicates a substantial increase in the frequency of the five lake-effect synoptic types and a long-term decrease in the numbers of cyclone synoptic types over the period 1950–1951 through to 1981–1982. Information concerning trends in the frequency and the intensity of each of the nine snowfall-producing synoptic types was combined to produce a modelled snowfall change due to frequency and intensity variations over the period. Trends in the frequency and intensity of the synoptic patterns associated with lake- effect snowfall explain the majority of the observed snowfall increase across the region. Variations in the synoptic types associated with cyclonically induced snowfall are shown to be unimportant to snowfall changes across the eastern Great Lakes area. Possible reasons for increases in the frequency and the intensity of the lake-effect synoptic types are discussed.