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

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Sunday, 4 January 2015
Shay A. Callahan, Hobart and William Smith Colleges, Geneva, NY; and E. P. Morrill and N. D. Metz

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. 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 the short-wave trough appeared to influence the relative changes in these characteristics. The purpose of this presentation is to give an overview of the changes in the lake-effect snow character as each short-wave trough passed and explore how well the first, most intense short-wave trough and associated lake-effect snow were forecast by numerical models.

Given that the first trough was the most pronounced, a detailed investigation of the 4-km NAM model forecasts of trough passage on 7 January was undertaken. This analysis revealed subtle differences in the positioning of the short-wave trough throughout the 36-h forecast period. However, the most pronounced error between the NAM forecasts and the actual pattern was actually in the amplitude of the downstream ridge. This lake-effect event began following the passage of a surface cold front. Diabatic heating associated with the front and surface low amplified this ridge in a manner that wasn't even captured by the 6-h forecast. This resulting amplification coupled with the sharp short-wave trough to the west resulted in a more 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 lake-effect snow band that had a different shape, orientation, and location than in the model forecasts.