The Impacts of the Passage of Three Distinct Short-Wave Troughs on a Prolonged Lake-Effect Snow Event during OWLeS

From 6 to 9 January 2014 during the field phase of the OWLeS project, three distinct short-wave troughs passed over Lake Ontario during a single extended lake-effect snow event. This event produced snowfall totals ranging from 6–60 inches within a 100-mile region. Ahead of each of these short-wave troughs, the lake-effect snow bands tended to increase in intensity, inland extent, and even mimic the trough curvature. The sharpness of each short-wave trough appeared to influence the relative changes in these characteristics. This presentation will give an overview of the changes in the lake-effect snow character as each short-wave trough passed. The primary focus will be on how the first, most intense short-wave trough influenced the boundary layer and how well numerical models handled lake-effect snow forecasts in the presence of this first short-wave trough passage.

Sounding data taken during the passage of this first short-wave trough shows that the boundary-layer depth increased ahead of the trough passage both north and south of the lake-effect band. This boundary layer deepening resulted in a rapid increase in convective intensity. Following the short-wave trough passage, both the boundary-layer depth and the resulting convective intensity decreased. Additionally, the short-wave trough had an influence on lake-effect snow maintenance in the presence of boundary-layer shear. Despite the 60–80° of boundary layer shear present, the lake-effect band reached its most intense stage as the short-wave trough approached. A detailed investigation of model forecasts during trough passage shows there were subtle differences throughout the 36-h forecast period, but the most pronounced error between forecasts and observations was in the amplitude of a downstream ridge. Diabatic heating associated with a front and surface low that preceded the lake-effect snow event likely amplified this ridge in a manner that was not even captured by the 6-h forecast. This resulting amplification coupled with the sharp short-wave trough to the west resulted in a highly curved flow and a distinctly different orientation to the lake-effect band than was captured in any model run. Thus, the lake-effect snow event began with a snow band that had a different shape, orientation, and location than what was present in the model forecasts.