chicago metro lake effect snow
9-10 november 2025
a remarkably primed thermodynamic environment, reminiscent of environments seen over lake erie, set the stage over lake michigan for an impressive early-season lake effect snow event. lake surface temperatures were anomalously warm for november, and an intrusion of unusually cold arctic air associated with a southern extension of the polar vortex swept across the great lakes basin.
as this cold air mass interacted with the warm lake surface, a mesolow formed over central lake michigan on 9 november. the deepening low enhanced lift and focused convergence, producing the first significant band of lake effect snow that reached the chicago area late that evening. this arcing band as a result of the deepening mesolow brought bursts of heavy snow, reducing visibility, and accumulating rapidly near the lakeshore.
through the night and into the early hours of 10 november, the mesolow drifted southward and synoptic forcing weakened. in its wake, sustained convergence along lake michigan’s major axis established a second, more organized snow band. this narrow but intense band acted like a “fire hose,” training repeatedly as it oscillated along the southwestern shoreline. by 13z on 10 november, the heaviest totals were reported across:
lake county, in (cedar lake): 12.3”
kankakee county, il (momence): 12.0”
lake county, il (winthrop harbor): 10.0”
these localized amounts sharply contrasted with official area reports - only 1.7” at both chicago o’hare international airport and nws chicago, a trace at rockford, and 2.5” from a co-op station southwest of midway.
outside of the convective bands, near-surface air remained dry (~20° T/Td spread), resulting in instances of virga, fall streaks, and a minimal snow accumulation across much of cook county, il despite radar returns indicating precipitation aloft. the convective intensity of the dominant band was evident early on 10 november, when lightning was detected near the lakeshore - a clear signal of thundersnow within the mature lake effect plumes.
