Storm-Track Variability in Synoptic Forcing During Heavy Lake-Effect Snow Events over Lake Michigan

Abstract

Lake-effect snow (LES) has traditionally been studied from a mesoscale perspective, with comparatively less attention devoted to the role of synoptic-scale forcing. This study quantifies the prevalence and magnitude of synoptic forcing during 116 heavy LES events affecting the eastern shore of Lake Michigan between 1997 and 2024. Events were identified from the NOAA Storm Events Database and classified into five storm-track categories: Alberta Clippers (ACs), Colorado Lows (COs), East Coast Lows (ECs), Great Lakes Lows (GLLs), and anticyclones (HIs). ERA5 reanalysis data extracted at each event onset were composited by storm track to evaluate 500 mb vorticity advection, 850 mb temperature advection, 700 mb Q-vector divergence, 700 mb omega, sea-level pressure, lake index, and specific humidity. Cohen’s d and a resampling bootstrapping procedure were used to quantify and evaluate differences among storm tracks. AC, CO, and GLL events consistently exhibited the strongest synoptic-scale forcing, characterized by enhanced cyclonic vorticity advection, Q-vector convergence, and upward vertical motion, whereas HI events displayed minimal dynamical forcing despite producing heavy LES. Conversely, GLL and HI events exhibited the greatest thermodynamic instability, while CO and EC events contained the highest ambient moisture. These results demonstrate that heavy LES develops through multiple pathways, with some storm tracks featuring prevalent synoptic forcing and others exceptionally favorable thermodynamic conditions.