Synoptically classified lake-effect snowfall trends to the lee of Lakes Erie and Ontario

Recent research has indicated that snowfall in portions of the North American Great Lakes region subject to lake-effect snow has undergone a trend reversal, with snowfall declining in recent decades. This study examines the seasonal variability and trends specifically in synoptically classified lake-effect snow across the eastern Great Lakes region, and investigates the mechanisms responsible for observed changes. Using a synoptic climatological approach, days are identified where the synoptic-scale conditions are conducive to lake-effect snowfall and the associated snowfall is analyzed. Seven synoptic types over the November to March snowfall season are identified with characteristics of lake-effect conditions. Snowfall from these 7 lake-effect synoptic types represents between 45 and 53% of the seasonal snowfall total along the eastern shores of Lakes Erie and Ontario, with snowfall totals being highest during January. Lake-effect snowfall exhibits a 60 yr increasing trend downwind of Lakes Erie and Ontario; however, through examination over shorter 30 yr periods, a change in the trend of snowfall is observed around 1980. While a true trend reversal is not detected, lake-effect snowfall significantly increases from 1950−1979 before exhibiting no significant trend from 1980−2009. The inter-annual variability of seasonal lake-effect snowfall is highly related to the frequency of lake-effect synoptic types where an increase (decrease) in synoptic type occurrence leads to enhanced (diminished) lake-effect snowfall totals. Depending on the period examined, long-term changes in the frequency of lake-effect synoptic types and snowfall rates represent between 89 and 95% of the observed changes in lake-effect snow.