Multiscale interactions in a lake-effect snowstorm

This study highlights the influence of a synoptic scale trough on the development and propagation of several mesoscale vortices during a major lake-effect snowstorm, which occurred from 16-18 January 2005. The storm, designated “Date” by the Buffalo, NY, National Weather Service Forecast Office, dropped 30 to 60 cm of snow along a 80-km swath west of Rochester, NY. The Buffalo Office described such large snowfall amounts in this climatologically unfavorable area for intense lake-effect as “almost unprecedented”.

The interaction between a mobile mid-level short-wave trough and a strong surface ridge of high pressure led to surface pressure troughing, a complex low-level wind field, and nearly 180 degrees of vertical directional shear over the Eastern Great Lakes. As the shear zone moved south and westward across the lake, it caused a pre-existing lake-effect snowband to stall and reverse orientation. Shortly thereafter, the band began to exhibit a wave-like structure, developing several meso-γ vortices. As the trough system intensified, these mesovortices grew in size, from less than 10 km in diameter to more than 20. The more developed vortices exhibited a preferential cyclonic tendency and rings of 15-30 dbZ reflectivity surrounding a nearly precipitation-free core. As winds backed to the north-northwest behind the surface trough, the vortices were driven inland and the lake-effect morphology transitioned to a series of wind-parallel rolls.

This case illustrates the complex behavior that can result from the interplay of synoptic scale features over the Great Lakes, as well as an example of a climatologically significant lake-effect snow storm occurring in a high-shear environment.