Synoptically Driven Lake Effect Snowfall Changes to the Lee of Lakes Erie and Ontario

Recent research has indicated that snowfall in portions of the Great Lakes region subject to lake effect snow has undergone a trend reversal, with snowfall declining in recent decades. This study confirms the trend reversal specifically for lake effect snow across the eastern Great Lakes region and investigates the mechanisms responsible for these observed snowfall changes. Using a synoptic climatological approach, snowfall events are classified by their synoptic conditions and those identified as lake effect synoptic conditions are isolated and analyzed. Seven synoptic types over the November – March snowfall season are identified as exhibiting lake effect conditions. Snowfall from the seven lake effect synoptic types represents between 45-53% of the seasonal snowfall total along the eastern shores of Lakes Erie and Ontario. Furthermore, this lake effect snow exhibits a similar trend reversal as noted in the literature. Directly east of Lake Ontario, lake effect snowfall increases by over 5.0 cm year^-1 from 1950-1979, then declines by over 1.0 cm year^-1 from 1980-2009. It is hypothesized and supported here that frequency and intensity of lake effect synoptic types predominately influence lake effect snowfall variability. The seasonal frequency of the lake effect synoptic types undergoes a similar change in trend as snowfall, where the frequency initially increases by 13 days from 1950-1979, then begins to decline after the 1980 winter season. Through producing a modeled snowfall change, it is shown that frequency and intensity changes of lake effect synoptic types accounts for the majority of observed lake effect snowfall changes.