If you've ever experienced the overwhelming "flash snowstorm" that is lake effect snow, you know that the sudden white-out conditions can disappear just as quickly as they came, a giant pile of freshly fallen snow the only evidence they were there at all. But how does it work? Here it is, explained in one picture.
NOAA put together this graphic that illustrates the entire process:
The picture does a nice job of showing just how the sequence works — and why it is that we get the "wall of snow" or the "rolling snowstorm" effect. In case you want words to go along with it, NOAA also has this explanation:
Lake-effect snow forms in the winter when cold air masses move over warmer lake waters. As the warm lake water heats the bottom layer of air, lake moisture evaporates into the cold air. Since warm air is lighter and less dense than cold air, it rises and begins to cool. The moisture that evaporates into the air condenses and forms clouds, and snow begins falling.
Video: Jason Holler & Joseph DeBenedictis.