There’s an old saying that “thunder in the winter brings snow in seven days,” and as you scan the sky for storms and pray for a snow day, you may be wondering, “Is thunder as a long-term weather predictor crazy, or nah?” You have reason to be skeptical: A lot of old wives tales, from “You should totally pee on that jellyfish sting” to “That gum you just swallowed will take seven years to digest,” are completely, 100 percent false. However, you’ll be thrilled to know that the people who made up old adages back in the day weren’t always wrong: It turns out that the whole “thunder in winter predicts snow in a week” is actually true.
Well, sort of.
Thunder in winter may not mean that snow is definitely coming in exactly one week, but it does do a pretty good job of predicting cold weather and snow. Kate Kershner at How Stuff Works explains that this adage has less to do with thunder itself than with the weather conditions that make thunderstorms possible. Kershner writes that winter thunderstorms happen when “cold air and low-pressure systems from the north [displace] warm air and high pressure in the south,” creating an “unstable atmosphere.” This atmosphere is great for storms, but it also means that the cold air from the north is replacing the warmer air from the south, creating a cold front. The Old Farmers Almanac explains that when a new weather system moves in a few days later (it could be seven days, but it could also be less or more), it will meet the cold front, which may have temperatures low enough to produce snow.
“Thundersnow,” a thunderstorm featuring snow instead of rain, is a fairly rare phenomenon, but a 2006 study found that when thundersnow does occur, it tends to be followed by heavy snow in the next 24 hours. So the next time you see snow accompanied by thunder and lightning, put on your warmest pajamas, make yourself a hot, boozy drink, and settle in for some quality binge watching. You may be in for a snow day.