Does Thunder in the Winter Mean Thunder Snow is Coming?

But that doesn't mean there isn't actually a little grain of truth in the phrase. Wintertime thunder does tell us a bit more about how the weather might behave than, say, a groundhog that sniffs its way out of a burrow once a year. Thunder, on the other hand, does in fact signal a certain type of weather front, which might give us a glimpse of the cold stuff.

The general idea is that thunder develops in atmospheres conducive to — surprise! — thunderstorms. You're not going to get a ton of the rumbly stuff on, say, a clear day with no chance of rain. However, cold air and low-pressure systems from the north, displacing warm air and high pressure in the south, form an unstable atmosphere that can create terrific conditions for thunderstorms. Now, that means if you're hearing thunder in the wintertime, it could signal that a cold front is moving in. A moist weather system making its way through next could conceivably bring snow showers. A safe prediction you could make when you hear thunder in wintertime? Some cold weather is on its way.

Naturally, the "seven days" thing is a bit of a stretch. While a cold front could signal some snow, there's certainly no predicting when (or if) another wet weather system could arrive. What we do know (according to one study) is that if you do get "thundersnow," you're likely to get dumped on quite heavily. However, the Royal Meteorological Society noted that thundersnows only account for 0.07 percent of snowstorms in the U.S.