A Seven-Year Climatology of the Impacts of Short-Wave Troughs on Lake-effect Snow Events off of Lake Ontario

In the Great Lakes region, lake-effect snow is a significant hazard to society for a substantial portion of the year. As lake-effect snow is usually thought of as a lower-tropospheric phenomenon, less focus is typically given to upper level features, such as short-wave troughs. The interaction of short-wave troughs with lake-effect snow can increase the depth of the near-surface unstable layer and result in ascent ahead of the short-wave trough potentially producing more intense lake-effect bands than previously anticipated.

To better understand the impacts of short waves, lake-effect snow events coinciding with these troughs were examined over Lake Ontario. During a seven-year (07/08–13/14) cold-season (October–March) climatology there were 177 short-wave troughs concurrent with lake-effect clouds. Of these cases, 132 produced radar returns off of Lake Ontario. The impacts of short-wave troughs on these lake-effect events were studied by utilizing a short-wave-relative reference frame.  Time t=0 was denoted as the time when a coherent vorticity maximum of at least 18 × 10⁻⁵s⁻¹ intersected the downwind shore of Lake Ontario. Using composite radar imagery from NOAA’s radar archive, inland extent, band orientation, band centroid latitude, and 20 DBZ reflectivity length, were recorded every three hours from t-6 to t+6. There was an increase in median inland extent of the 132 lake-effect bands from 0 km at t-6 to 108.72 km at t+6, while the median 20 dBZ reflectivity length increased from 0 km at t-6 to 22.4 km at t+6.  These results indicate that lake-effect snow bands often initiate as a short-wave trough passes the downwind shore of Lake Ontario.  Out of the 132 cases, 36 featured snowfall during all five time periods (t-6 through t+6). These 36 cases also saw increases in inland extent and 20 dBZ reflectivity length at the t=0 time period. Furthermore, the lake-effect bands tended to shift southward and rotate counter-clockwise as the short-wave trough moved overhead.