Some of the most intense local snowstorms in the Great Lakes region occur through complex interactions between lake-effect boundary layers and nearby synoptic-scale cyclones. One such lake-enhanced snowstorm developed over Lake Michigan on 5 December 1997 during the Lake-Induced Convection Experiment (Lake-ICE). Field operations allowed the first detailed observations of the effects of a synoptic cyclone on the lake-effect convective boundary layer (CBL). In situ aircraft data, project soundings, airborne dual-Doppler radar (ELDORA) and operational radar and satellite data were utilized to document interactions between higher-level precipitation generated by the cyclone and the CBL. In spite of relatively modest total surface heat fluxes of 100-200 W m^-2, cross-lake CBL growth was greatly accelerated as the lake-effect CBL merged with an overlying reduced-stability layer, producing a mean CBL growth rate of 1.15% across the lake. This rate was faster than most previously reported, even in cases with much stronger surface heat fluxes.

Radar and aircraft observations indicate that portions of the lake-effect CBL were seeded by snow from higher-level cloud decks over the upwind (western) regions of Lake Michigan. Portions of nearly constant-altitude aircraft flight legs, taken within seeded and non-seeded regions, were compared to reveal the influence of seeding on the CBL thermal and microphysical structure. Two major influences of seeding were noted. The CBL was estimated to be approximately 15% deeper in seeded regions relative to nearby unseeded areas. In addition, water-equivalent precipitation rates were ~5 to 35 times greater in seeded regions than non-seeded regions, based on aircraft in situ precipitation probe observations. A maximum snowfall rate of 40.8 mm d^-1 was observed, comparable to rates previously reported for intense midlake/shoreline band lake-effect events.