On the Frequency of Lake-Effect Snowfall in the Catskill Mountains

Meltwater from snow that falls in the Catskill/Delaware Watershed in the Catskill Mountains in south-central New York contributes to reservoirs that supply drinking water to approximately nine million people in and near New York City (NYC). Using the Interactive Multisensor Snow and Ice Mapping System (IMS) 4km snow maps from the National Oceanic and Atmospheric Administration's National Ice Center, we identified and tracked 28 lake-effect (LE) storms that deposited snow in the Catskill Mountains from 2004-2017. These storms, that generally originated from Lake Ontario, but sometimes from Lake Erie, represent an underestimate of the number of LE storms that contribute snowfall to the total Catskills snowpack because snowstorms are not visible on the IMS maps when they travel over already-snow-covered terrain. Using satellite, meteorological (including NEXRAD and National Weather Service Cooperative Observer Program), and reanalysis data we identify conditions that contributed to the LE snowstorms and map snow-cover extent (SCE) following the storms when possible. IMS 4km maps tend to overestimate SCE compared to MODerate-resolution Imaging Spectroradiometer (MODIS) and Landsat. Though the total amount of snow from each LE snow event that contributes snow to the Catskills is often small, there are a large number of events in some years that, together, add up to a great deal of snow. Changes that are predicted in LE snowfall events could impact the distribution of rain vs. snow in the Catskills which may affect future reservoir operations in the NYC Water Supply System and winter recreation in the Catskills.