How long does lake effect snow last?

Answer 1

It lasts as long as the synoptic setup persists. Sometimes a band can only stay together for a few hours, while it is not that uncommon for a snow band to persist for a couple days, simply oscillating in location as the wind direction varies slightly. Usually these bands either get shut off because the wind direction shifts it off the lake, or because there is not enough moisture or lift in the atmosphere to generate the clouds and precipitation. It is difficult for the latter to remain favorable for more than a couple days, hence why you don't get lake effect snow for a week even though the wind might remain off the lake.

Currently I believe there is an extended period of lake effect and upslope snow over the Great Lakes. There is a deep upper level trough over this part of the country, and a ton of shortwaves (which provide energy and lift) rotating around it which are giving pulses of off and on snow showers depending on the location. While bands themselves don't last all that long, the threat of snow showers can persist for even a couple weeks when these patterns get "locked in" as it appears to be right now.