The wind's path over the lakes is important. More moderate lake-effect snows occur every fall under less extreme thermal contrasts. This often happens in late fall, when lake water is still warm from summer and cold air starts sweeping down from Canada. A difference of 25 degrees Fahrenheit (14 Celsius) or more creates an environment that can fuel heavy snows. Rawlins, a climate scientist at UMass Amherst, writes lake-effect snow is strongly influenced by the differences between the amount of heat and moisture at the lake surface and in the air a few thousand feet above it.Ī big contrast creates conditions that help to suck water up from the lake, and thus more snowfall. As the bitter cold air sweeps across the relatively warmer Great Lakes, it sucks up more and more moisture that falls as snow. It starts with cold, dry air from Canada. The phenomenon is called 'lake-effect snow,' and the lakes play a crucial role.
