Synoptic climatology of lake-effect snowfall conditions in the eastern Great Lakes region

The characteristics of overlying synoptic conditions play an important role in the production of lake-effect snowfall within the Great Lakes region of North America. With a synoptic climatological approach, the synoptic-scale patterns conducive to lake-effect snowfall are identified for the eastern Great Lakes region during the November-March seasons of 1950-2009. Seven synoptic types identified as lake effect are combined with daily snowfall observations to examine the role of individual synoptic types on seasonal snowfall. The types exhibit a wide range of surface and 850 hPa temperatures and winds, sea-level pressures, snowfall intensities, and inter-annual frequencies. These factors result in substantial differences in the location and magnitude of seasonal lake-effect snowfall. Recent research has revealed that snowfall within portions of the Great Lakes region subject to lake-effect snow has undergone a trend reversal, declining in recent decades. Examining the inter-annual frequency of the seven lake-effect synoptic types, a majority of types increased in frequency prior to 1980, before becoming less frequent thereafter. The variability in frequency of lake-effect synoptic types can partially be explained by relationships to large-scale atmospheric and oceanic modes of variability. The majority of lake-effect synoptic types occur in association with an upper-level trough over the eastern United States. This trough is consistent with the upper-level pattern associated with a negative phase Arctic Oscillation (AO) and North Atlantic Oscillation (NAO), or positive Pacific/North American pattern (PNA), such that when the AO, NAO, and/or PNA pattern are in those respective phases, there is a significant increase in the frequency of lake-effect synoptic types.