Short-Wave Troughs and Lake-Effect Snow in the Great Lakes Region

Lake effect snow is a significant hazard to the public in the Great Lakes region and presents a forecasting problem for operational meteorologists as small changes in environmental conditions can have drastic effects on lake-effect snow bands. 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. These middle and upper tropospheric features can still impact relatively shallow lake-effect snowstorms, changing the depth of the unstable layer and resulting in increased ascent ahead of the short wave. The purpose of this presentation is to present a seven-year climatology of the interactions between short-wave troughs and lake-effect snow events to identify how often these interactions occur.

A total of 608 short-wave troughs crossed the Great Lakes region during the cold seasons (October–March) of 2007/08 through 2013/14. The winter of 2013/14 had the most short-wave trough events with 116, while the winter of 2008/09 had the fewest with only 74. This climatology further examined days when lake-effect clouds from a Great Lake were apparent on visible satellite imagery and a short-wave trough with vorticity values of at least 18 × 10⁻⁵ s⁻¹ intersected the same Great Lake. In total, 380 of the 608 short-wave troughs met these criteria on at least one Great Lake. On average, these 380 short-wave troughs crossed 3.66 lakes that also had lake-effect clouds present on the same day. These interactions occurred most frequently in January and least frequently in March. Lake Michigan had the greatest number of occurrence (282) of a short-wave trough crossing the lake concurrently with lake-effect clouds present. It was most common for a short-wave trough to intersect all five Great lakes with lake-effect clouds present, and least common for only one Great Lake with lake-effect clouds present to be intersected by a short-wave trough. Thus, a short-wave trough entering the Great Lakes region in the cold season presents an important forecasting issue given its likelihood of crossing multiple Great Lakes with ongoing lake-effect precipitation.