Lake effect snowfalling (cold air over warm water) is a common cause of turning a typical thunderstorm into a thundersnow storm.
In these cases — more commonly experienced by people living in northwestern Europe or near the North American Great Lakes region and similar environments — air rises quickly when contacting relatively warm water surface temperatures.
Cold air aloft (near the top of the cumulus cloud), as well as steep lapse rates as the air temperature cools rapidly in its climb, create favorable conditions for a storm with greater destructive potential.
