A SYNOPTIC CLIMATOLOGICAL APPROACH TO THE ANALYSIS OF LAKE-EFFECT SNOWFALL - POTENTIAL FORECASTING APPLICATIONS

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 ca se along the southern and eastern shores of Lakes Erie and Ontario in the northeastern region of the United States. Here a synoptic climatol ogical approach is used to identify the synoptic-scale atmospheric pat terns conducive to lake-induced snowfall to the lee of Lakes Erie and Ontario in the states of New York and Pennsylvania from November to Ma rch. The approach used in this study allows for a thorough investigati on 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 hei ghts, and 500-mb heights. By combining the lake-effect synoptic types with daily snowfall data for 159 stations across New York and Pennsylv ania, 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 rake-effect snowfall in western New York and northwestern Pennsylvania. The large-scale synop tic situation is similar for each lake-effect type; however, each can be clearly distinguished by its wind components, which are important f actors in the spatial pattern and intensity of lake-effect snowfall. V ariations 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 t he lake-effect types occur most often in midwinter, while two are most frequent near the beginning and/or end of the snowfall season. Additi onally, the interannual frequencies of the midwinter types indicate an upward trend that coincides with evidence of a lake-effect snowfall i ncrease during midseason over the past century. The authors believe th at the differences in the lake-effect synoptic types outlined here can be used as additional guidance for more accurate extended forecasts o f lake-effect snowfall in northwestern Pennsylvania and western New Yo rk.