SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/hike-thirty-thirty-rule

In the 30 30 lightning rule, what does the first 30 mean?

Thunder 30 seconds or less after a flash means seek shelter immediately.

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  1. Wait 30 minutes before hiking
  2. Stay 30 feet from trees
  3. Thunder within 30 seconds of a flash ✔

Why: Count from the lightning flash to the thunder. If it is 30 seconds or less, the storm is close: get to shelter now. The second 30 means danger lasts 30 minutes after the last lightning or thunder.

Huh, didn't know that: The National Weather Service now teaches a simpler rule: if you hear any thunder at all, go indoors.

The dad joke
I tried counting between lightning and thunder, but I kept losing count. It was a real flash in the pan.
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References

Answer: Thunder within 30 seconds of a flash. Count from the lightning flash to the thunder. If it is 30 seconds or less, the storm is close: get to shelter now. The second 30 means danger lasts 30 minutes after the last lightning or thunder.

  1. NPS Grand Canyon: Lightning Danger www.nps.gov/grca/planyourvisit/lightning-danger.htm
    If the sound of thunder follows a lightning flash in 30 seconds or less, seek shelter immediately.
    Checked 2026-10-12.
  2. NWS: Lightning Safety www.weather.gov/safety/lightning-safety
    When Thunder Roars, Go Indoors.
    Checked 2026-10-12.

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