LAUSR

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.