American Meteorological Society Certification (AMS) Practice

Lake-effect snow occurs as a result of cold air moving over a relatively warmer lake. In this process, the cold air picks up moisture from the surface of the lake, which has been warmed by the sun during the warmer months. As the cold air moves over the warmer water, it gains heat and moisture, becoming unstable. Once the air is lifted over the land, it cools and condenses, leading to the formation of clouds and ultimately precipitation in the form of snow. This phenomenon is particularly notable in regions where the lakes are still relatively warm while the surrounding air is significantly colder, especially during the late fall and winter months.

Other options do not correctly describe the mechanisms behind lake-effect snow. For instance, warm air moving over a cold lake typically doesn’t create the same conditions necessary for heavy snowfall, and the influence of coastal heavy rains or mountain ranges does not directly account for the localized conditions that give rise to lake-effect snow.