Lightning can strike around 10 miles away from a thunderstorm, and sometimes even farther, so if you hear thunder you are already close enough to be in danger.

A simple rule:

  • 5 seconds between flash and thunder = about 1 mile.
  • 30 seconds = about 6 miles, which is still risky.
  • If you hear thunder, go indoors right away.

Quick Scoop

Lightning is not limited to the rain core of a storm; it can hit from a clear- looking sky. Safety guidance says to treat thunder as an immediate warning sign and seek shelter without waiting.

Safe distance rule

The safest practical rule is:

  • Thunder heard = lightning is close enough to strike.
  • Some sources warn lightning may strike up to 25 miles from a storm in rare cases, which is why “far away” does not always mean safe.

What to do

  • Get inside a substantial building or hard-topped car.
  • Avoid open fields, water, trees, and metal objects.
  • Wait at least 30 minutes after the last thunder before going back outside.