Spring’s wacky weather sometimes leads to a confusing mish-mash of seasons all at once. Around this time of year, it’s not uncommon to hear thunder—or witness a full-on thunderstorm—when it’s kind of chilly outside. You’ve probably noticed that thunder always seems a bit louder when temperatures are on the cooler side, and there’s a good reason for it.
Thunderstorms form when air rapidly rises through the atmosphere. The resulting updraft allows clouds to grow high enough that ice crystals form. These ice crystals bumping and rubbing against one another build up a powerful static charge that releases as a bolt of lightning.
While we’re used to thunderstorms on a warm and humid afternoon, it doesn’t always have to be warm out for a thunderstorm to form. Springtime weather is dynamic. There are always powerful low-pressure systems swirling about, and dramatically different airmasses colliding with one another.
Powerful cold fronts can trigger thunderstorms even when the air isn’t all that unstable. We can even see “elevated thunderstorms,” which occur when warm air above the surface provides the instability necessary for storms to form and thrive. These elevated thunderstorms form during an inversion, which is the key to giving thunder its distinct roar when it’s chilly outside.
An inversion occurs when temperatures increase with height. We see inversions all the time when it’s cooler outside. Warm air is less dense than cold air, so it tends to ride over top a stubborn layer of cold air wedged at the surface. When a thunderstorm forms over or near an inversion, the sharp contrast in temperatures actually affects the sound of the thunder.
Inversions can actually trap the sound of thunder close to the surface, allowing the thunder to reverberate off the inversion and continue echoing for many miles away from the storm itself. It’s kind of like shouting in an empty room—just like our voices sound louder when they echo against the barren walls, thunder sounds louder when it echoes off an inversion and stays close to the ground.
This “trapped” thunder can sometimes continue on for dozens of miles away from a thunderstorm, being heard in areas where there’s no rain falling at the time. These seemingly mysterious booms often result in panicked reports on social media (or even calls to emergency services!) from folks concerned that there was an explosion nearby, because it’s not readily apparent that it was just thunder.
The next time thunderstorms are in the forecast when temperatures are on the cooler side, make sure to listen up for the roar of a nearby storm and enjoy the enhanced sound of nature’s wondrous ferocity.