Which weather phenomenon produces snow on the downwind side of the Great Lakes?

Lake-effect snow produces heavy snowfall on the downwind side of the Great Lakes.

The process begins when very cold air moves over relatively warmer, unfrozen lake water. Heat and moisture rise from the lake into the lower atmosphere, where clouds form. Winds then carry those narrow snow bands toward shore, sometimes concentrating intense snowfall over a small area.

The most affected locations include parts of western and central New York, northeastern Ohio, northwestern Pennsylvania, and Ontario. Snow totals can differ dramatically between nearby towns because bands may remain narrow and shift with wind direction.

Lake-effect snow usually weakens after a lake freezes, because open water is needed to supply heat and moisture. It is different from ordinary snow caused by a large regional storm, although the two processes can occur together.