Due to their mesoscale nature, forecasting lake-effect snowfall events is very difficult but extremely important to the inhabitants of those regions subject to this type of severe winter weather. Such is the case along the southern and eastern shores of Lakes Erie and Ontario in the northeastern region of the United States. Here a synoptic climatological approach is used to identify the synoptic-scale atmospheric patterns conductive to lake-induced snowfall to the lee of Lakes Erie and Ontario in the states of New York and Pennsylvania from November to March. The approach used in this study allows for a thorough investigation of the characteristics of each lake-effect synoptic type, including the intrannual and interannual variations in frequency and composite atmospheric fields of sea level pressures, 850-mb temperatures and heights, and 500-mb heights. By combining the lake-effect synoptic types with daily snowfall data for 159 stations across New York and Pennsylvania, direct associations are made between each synoptic type and the mean snowfall and snowfall frequency across that region. Five synoptic types are identified as producing significant lake-effect snowfall in western New York and northwestern Pennsylvania. The large-scale synoptic situation is similar for each lake-effect type; however, each can be clearly distinguished by its wind components, which are important factors in the spatial pattern and intensity of lake-effect snowfall. Variations in the sea level pressure patterns, 850-mb temperatures and heights, 500-mb heights, seasonality, and overlake fetch and strength of flow result in significant differences in the location, magnitude, and frequency of the snowfalls associated with these types. Three of the lake-effect types occur most often in midwinter, while two are most frequent near the beginning and/or end of the snowfall season. Additionally, the interannual frequencies of the midwinter types indicate an upward trend that coincides with evidence of a lake-effect snowfall increase during midseason over the past century. The authors believe that the differences in the lake-effect synoptic types outlined here can be used as additional guidance for more accurate extended forecasts of lake-effect snowfall in northwestern Pennsylvania and western New York.