It’s deep in winter, and a nor’easter is dumping snow outside. In between the howling winds, you hear a boom. Maybe a heap of snow fell from the roof, you think, or a giant icicle crashed from the eaves. A few minutes later, another boom pounds through the blizzard’s gales. It’s closer this time, and it seems to resound from the sky. This booming may be a rare wintertime phenomenon: thundersnow.

While most of us equate thunderstorms with hot, humid, summer weather, they can also happen during the winter. Thundersnow is, simply, a type of thunderstorm where precipitation falls as snow rather than rain. The thunder and lightning of a thundersnow storm result from the same factors that cause rainy thunderstorms. Regardless of the season, lightning in any storm requires electrical charge separation, explains Peter Banacos, science and operations officer at the National Weather Service in Burlington.