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Does Thunder Come After Lightning?

Lightning and thunder always seem to arrive in the same order, and there's a fun reason why

EARTH & WEATHER

9/19/20262 min read

A powerful white lightning bolt striking from dark storm clouds above a silhouetted suburban neighborhood at night.
A powerful white lightning bolt striking from dark storm clouds above a silhouetted suburban neighborhood at night.

Why Does Thunder Come After Lightning?

Have you ever watched a thunderstorm from your window? First, a bright flash lights up the sky. Then, a few seconds later, comes a big BOOM or a long, rumbling growl. Lightning and thunder always seem to arrive in the same order, and there's a fun reason why.

Thunder and Lightning Are Twins

Here's a surprise: lightning and thunder happen at exactly the same moment! They're like twins born at the same time. But you don't notice them at the same time, because one of them is much faster than the other.

What Makes the Flash?

Inside a storm cloud, tiny bits of ice bump and rub together, building up a huge amount of electricity. When there's too much to hold, it zooms out as a giant spark. That spark is lightning!

Lightning is incredibly hot, about five times hotter than the surface of the Sun. It heats the air around it in a split second.

What Makes the Boom?

When air gets that hot that quickly, it swells up super fast and shoves the cooler air out of the way. This creates a powerful wave of sound that travels through the air, like a giant invisible ripple. That sound is thunder! It rumbles because the lightning bolt is very long, so the sound reaches you from different parts of it at slightly different times.

The Great Race: Light vs. Sound

Now for the big race. Light is the fastest thing in the universe. It could zoom around the whole Earth about seven times in a single second! Sound is much slower. It travels about one kilometre every three seconds.

So when lightning strikes, the light reaches your eyes almost instantly. But the sound has to wobble its way through the air, and that takes longer. Light wins the race every single time, and that's why you see the flash first.

Try This: Count the Distance!

You can use this to figure out how far away a storm is:

  1. When you see a flash of lightning, start counting slowly: "One... two... three..."

  2. Stop counting when you hear the thunder.

  3. Divide your number by 3. That's about how many kilometres away the lightning was.

If you count to nine, the lightning was about three kilometres away. If the thunder comes almost right away, the storm is very close!

Stay Safe

If you can hear thunder, you're close enough to be in danger from lightning. Head indoors and stay away from windows, and wait about 30 minutes after the last rumble before going back outside.

The Big Idea

Thunder doesn't really come after lightning. They happen together. Sound just takes a little longer to travel to your ears. So next time there's a storm, be a weather detective and count the seconds!