Lightning, decoded. If you hear thunder, you are already in range.

Thunder is not the warning before the danger. Thunder IS the warning that lightning is already close enough to reach you. Every bolt is a giant spark looking for the fastest path to the ground, and it can travel miles from the storm you are watching. This page is the short version of what it is, how far it reaches, and what to do when you hear it.

WHAT IT ACTUALLY IS.

A spark, scaled up to the sky.

Inside a tall storm cloud, ice crystals and soft hailstones collide thousands of times, and the collisions separate electric charge — negative charge pooling low in the cloud, positive charge high up and on the ground below. When the difference gets big enough, the air itself breaks down and a bolt jumps the gap, heating the air around it to several times hotter than the surface of the sun in a fraction of a second. That sudden heating makes the air explode outward, and the sound of that explosion is thunder — which is why you never get lightning without thunder, even if the thunder arrives seconds later.

HOW FAR IT REACHES.

The storm you see is not the edge of the danger.

Lightning does not stay inside the rainy part of the storm. Bolts can strike the ground 10 miles or more from the rain core, which is how people get caught on a sunny beach or a golf course while the storm still looks far away — the so-called bolt from the blue. A useful rule of thumb: count the seconds between the flash and the thunder and divide by five, and that is roughly how many miles away the strike was; if the gap is 30 seconds or less, about six miles, the storm is close enough to reach you. That is also why the official advice is so blunt: when thunder roars, go indoors, and stay inside for 30 minutes after the last thunder you hear, because the storm can still throw a bolt while it looks like it is leaving.

WHAT TO DO ABOUT IT.

No place outside is safe. A car is not a lightning rod myth, either.

The only safe places are a substantial building with wiring and plumbing, or a hard-topped metal car with the windows up — and the car works because the metal shell carries the current around you, not because of the rubber tires, so a convertible, a golf cart, or a tent offers no protection at all. If you are caught outside with no shelter, get low, stay away from tall isolated objects and water, and do not lie flat — crouching low makes you a smaller target than standing tall. Brzzy’s forecast, live radar, and severe weather alerts turn the same kind of ground truth into a plain-language answer before the sky turns: go outside, or wait it out.

What is lightning?

Lightning is a giant electrical spark between a storm cloud and the ground, or between clouds. Collisions between ice crystals and hailstones inside a tall storm cloud separate electric charge, and when the difference gets big enough, a bolt jumps the gap, heating the surrounding air far hotter than the surface of the sun in a fraction of a second.

How far can lightning strike from a storm?

Lightning can strike the ground 10 miles or more from the rainy core of the storm, which is why a storm that looks far away can still reach you. Count the seconds between the flash and the thunder and divide by five for a rough distance in miles; a gap of 30 seconds or less means the strike was about six miles away or closer.

What should I do when I hear thunder?

Go indoors immediately — thunder means lightning is already close enough to reach you. Stay inside a substantial building or a hard-topped metal car, and wait 30 minutes after the last thunder you hear before going back outside, because a departing storm can still throw a bolt.

Is a car safe from lightning?

A hard-topped metal car with the windows up is reasonably safe, because the metal shell carries the current around the people inside — not because of the rubber tires. A convertible, golf cart, motorcycle, or tent offers no protection. The safest place is always a substantial building with wiring and plumbing.

Does Brzzy show lightning?

Brzzy shows your local forecast with hourly updates, live radar, severe weather alerts, GIF forecasts, and activity ratings that weigh the sky for your plans. Brzzy is free to download on iPhone.