Lake Effect Snow events are snowstorms that form on the downwind side of a body of water with a concave coastline. These events are very localized, extending from just a couple of miles up to 30 miles and only a few miles wide. In the most extreme cases, the bands can extend 100 miles inland and about 30 miles wide. Related to lake effect snow (e.g. Great Lakes and Great Salt Lake) are bay effect snow (e.g. Chesapeake Bay and Cape Cod Bay) and ocean effect snow (Gulf Stream).
The following 5 steps are a high-level look at the process of how lake effect snow is formed.
Cold air moves across the warm lake water. The air warms becomes less dense and rises, and also becomes humid.
As the air rises, it begins to cool. This cooler and moister air starts to condense and forms fog, which eventually creates clouds over the lake.
Once the air moves over land, this moisture in the air will continue to condense and form precipitation, snow.
As the warmed air reaches the shoreline, the air moves slower due to the increase in the friction between the water and land. This causes the air to concentrate in certain areas.
Higher land and hills (changes in topography) on the leeward side of the lake force the air upward. This causes the air to cool further leading to further cloud formation and increased snowfall.