This study has investigated the spatiotemporal structure and changes in Lake Michigan snowfall for the period 1950–2013. With data quality caveats acknowledged, a larger envelope of stations was included than in previous studies to explore the data using time series analysis, principal component analysis, and geographic information systems. Results indicate warming in recent decades, a near-dearth of serial correlation, midwinter dependence on teleconnection patterns, strong sensitivity of snowfall to temperature, peak snowfall variability and dependence on temperature within the lake-effect belt, an increasing fraction of seasonal snowfall occurring from December to February, and temporal behavior consistent with the previously reported trend reversal in snowfall.

This study has investigated the spatio‐temporal variability of November and March Lake Michigan snowfall for the period 1950–2013. Snowfall characteristics were assessed using time series analysis, geographic information systems, and visualization. Results indicate significant temporal decreases of November and March snowfall, peak inter‐annual variability within the lake‐effect belt, modest concurrent and lagged sensitivity to teleconnection indices, and strong dependence of snowfall on temperature. The decreased snowfall is in contrast to December–February snowfall and associated with a decreasing fraction of November and March precipitation days occurring as snow days, rather than changes in precipitation frequency. The decreasing fraction of precipitation days occurs as snowfall is consistent with synoptic‐scale disturbances producing rain rather than snow and lake‐effect rain falling in lieu of snow.

The substantial impact of Lake‐effect snow in the Laurentian Great Lakes has led to interest in the impact of climate change on snowfall in the region. A recent assessment of Lake Michigan snowfall revealed a marked decrease in November snowfall since the 1950s, associated with a warming‐induced reduction in the fraction of precipitation days occurring as snowfall. Herein, in order to identify the trend contribution from Lake‐effect snowfall, snow days from the November 1950–2012 study period are classified as primarily System or Lake‐effect, with additional options of Insignificant, Both, Remnant, and Unclear. The classification is based on the snowfall distribution and visual map inspection for synoptic‐scale forcing, and results are compared with an objective classification based on clustering of daily snowfall. The regional snowfall patterns of Lake‐effect and System snow days are markedly different, with Lake‐effect snow days exhibiting a clear Lake‐effect signature downwind of Lake Michigan. The larger‐scale environments also differ, with much colder conditions in the Great Lakes and higher sea‐level pressure in the Great Plains on Lake‐effect days. With snowfall projected onto the classifications, the decrease of snowfall east of the lake is attributable to both reductions in Lake‐effect and System snowfall, while System snowfall changes are dominant west of the lake. The trends are consistent with the sensitivity to regional temperature, as well as an increasing prevalence of rain reports (within other sub‐regions) during snow days. Results based on the objective classification are largely congruent.

The Laurentian Great Lakes have substantial influences on regional climatology, particularly with impactful lake-effect snow events. This study examines the snowfall, cloud-inferred snow band morphology, and environment of lake-effect snow days along the southern shore of Lake Michigan for the 1997–2017 period. Suitable days for study were identified based on the presence of lake-effect clouds assessed in a previous study and extended through 2017, combined with an independent classification of likely lake-effect snow days based on independent snowfall data and weather map assessments. The primary goals are to identify lake-effect snow days and evaluate the snowfall distribution and modes of variability, the sensitivity to thermodynamic and flow characteristics within the upstream sounding at Green Bay, WI, and the influences of snowband morphology. Over 300 lake-effect days are identified during the study period, with peak mean snowfall within the lake belt extending from southwest Michigan to northern Indiana. Although multiple lake-effect morphological types are often observed on the same day, the most common snow band morphology is wind parallel bands. Relative to days with wind parallel bands, the shoreline band morphology is more common with a reduced lower-tropospheric zonal wind component within the upstream sounding at Green Bay, WI, as well as higher sea-level pressure and 500-hPa geopotential height anomalies to the north of the Great Lakes. Snowfall is sensitive to band morphology, with higher snowfall for shoreline band structures than for wind parallel bands, especially due south of Lake Michigan. Snowfall is also sensitive to thermodynamic and flow properties, with a greater sensitivity to temperature in southwest Michigan and to flow properties in northwest Indiana.