The Impact of a Short-Wave Trough on Boundary-Layer Evolution during a Lake-Effect Snow Event

During the 6–9 January 2014 period, a prolonged, intense lake-effect snow event occurred along the eastern shore of Lake Ontario. This event produced snowfall totals ranging from 6–60 inches within a 100-mile region. This event was associated with a wide range of band intensities as well as changes in band shape and location. One cause for these fluctuations was the three distinct short-wave troughs that passed through the Lake Ontario region during this four-day period. The first of these three short-wave troughs was the most intense and will serve as the focus of this presentation. The objective of this study is to demonstrate the evolution of the lake-effect snow band before, during, and after this trough passage and relate this evolution to changes in the boundary layer during the same period of time.

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. Furthermore, the short-wave trough had an influence on lake-effect snow maintenance in the presence of boundary-layer shear. Conventional wisdom suggests that boundary-layer directional shear in excess of 60° will destroy lake-effect snow. However, the lake-effect band reached its most intense stage as the short-wave trough approached and 60–80° of boundary layer shear was present. Likely, the approaching short-wave trough created a favorable dynamical environment, which allowed the lake effect to persist in spite of an unfavorable shear environment.