In this article · 5 sections
For years the 30-30 rule was the lightning rule most coaches, officials and groundskeepers could recite. It has two halves, and they have aged very differently.
What the 30-30 rule said
The first 30 was a count. When you saw a flash, you counted the seconds until you heard its thunder. If the gap was 30 seconds or less, the storm was close enough to be dangerous and you went inside. The second 30 was a wait: stay in shelter for at least 30 minutes after the last thunder before going back out.
Older National Weather Service material presented it as the best lightning guidance for the general public, and an NWS public notice from 2006 called it one of the best rules to follow outdoors, with a caveat that is easy to miss: use it only when visibility is good and nothing blocks your view of the storm.
The arithmetic behind the count is simple. Sound covers about a mile every 5 seconds, so a 30-second gap puts the flash roughly 6 miles away. Our lightning distance calculator does the sum for any count.
- 5 sfor thunder to travel about a mile
- 30 sflash-to-thunder gap, about 6 miles
- ~10 mihow far thunder is normally heard
- 30 minwait after the last thunder
Why the first 30 moved on
The count has a timing problem. The NWS says lightning can strike outward about 10 miles from a thunderstorm, and that thunder is normally heard about 10 miles from a strike. A 30-second gap means the flash is around 6 miles away, so by the time the count says "go", the storm has usually been close enough to strike for a while.
It also depends on conditions a game rarely gives you. You need to see the flash and hear its thunder, match the two, and count accurately. The NCAA lightning guideline points out that thunder can be hard to hear during an event, especially in a stadium with a large crowd.
So current guidance acts on the evidence itself, not on a count. The NFHS guideline for high schools treats hearing thunder or seeing lightning as the sign that the storm can reach you: suspend play and move everyone to the safer location at once. The National Athletic Trainers’ Association (NATA) position statement says that if you can hear thunder, you are close enough to be in danger and should get to a safe place immediately. NOAA’s lightning safety guidance makes the same point: hearing thunder is your warning.
| Attribute | The 30-30 rule | NFHS guideline (Oct 2024) | NATA position statement (2013) |
|---|---|---|---|
| When to go inside | Flash-to-thunder gap of 30 seconds or less | As soon as thunder is heard or lightning is seen | As soon as thunder can be heard; everyone fully inside by the time the storm edge is about 5 nautical miles away |
| When to come back out | 30 minutes after the last thunder | At least 30 minutes after the last thunder or lightning | 30 minutes after the last lightning within 5 nautical miles and the last thunder |
| Does the clock reset? | Not spelled out | Yes, on any new thunder or lightning | Yes, on each nearby flash and each thunder |
The 30-30 rule
- When to go inside
- Flash-to-thunder gap of 30 seconds or less
- When to come back out
- 30 minutes after the last thunder
- Does the clock reset?
- Not spelled out
NFHS guideline (Oct 2024)
- When to go inside
- As soon as thunder is heard or lightning is seen
- When to come back out
- At least 30 minutes after the last thunder or lightning
- Does the clock reset?
- Yes, on any new thunder or lightning
NATA position statement (2013)
- When to go inside
- As soon as thunder can be heard; everyone fully inside by the time the storm edge is about 5 nautical miles away
- When to come back out
- 30 minutes after the last lightning within 5 nautical miles and the last thunder
- Does the clock reset?
- Yes, on each nearby flash and each thunder
Flash-to-bang counting has not disappeared. Some NWS pages still teach it as a way to estimate how far away a strike was, and the version of the NCAA guideline we reviewed still treats a 30-second gap as the latest point by which everyone should already be in shelter. What has changed is its role: it is a distance estimate, not the signal to start moving.
The half that still applies: 30 minutes
The second 30 is still how outdoor activity resumes. Every guideline we reviewed asks for at least 30 minutes after the last thunder or lightning, and each new rumble or flash starts the count again. The NWS guidance for sports says experts agree on the 30-minute wait, and NFHS spells out the reset: any thunder or lightning after the count begins means a new 30-minute count.
- Start the clock at the last thunder or lightning, not when the rain stops or the sky brightens.
- Restart it every time there is new thunder or lightning nearby.
- At night, flashes can be seen from storms too far away to be a threat. NFHS and NCAA both note that lightning seen with no thunder may be out of range; NFHS adds that independently verified detection data removes the uncertainty.
- Write the wait into your policy so the person making the call is applying a rule, not a judgement.
The second 30
A clearing sky does not stop the clock. The last strike starts it.
Where detection data and prediction fit
Both NFHS and NATA leave room for technology. The NFHS guideline says that where a nationally connected lightning detection network is available, it should be watched when storms are possible: suspend play when lightning is within 10 miles and resume only after 30 minutes with no lightning inside that radius. It also says what you see and hear always comes first: if the sky looks threatening or you hear thunder, a device or app does not overrule that. NATA recommends considering a commercial real-time lightning service that has been independently and objectively verified.
That is where Flash Lightning Prediction sits. It forecasts strikes up to 60 minutes ahead for each 1×1 km cell, refreshed every 2 minutes, and is scored against NLDN ground-truth strikes, with up to 99.6% accuracy on the one-hour window. The scoring method is on the accuracy method page. The point of the lead time is to start the move to shelter before thunder is in earshot, so everyone is already inside when the guideline says they must be.
Prediction does not shorten the second 30. Each Flash site carries its own radius and all-clear wait, and the return-to-play timer starts from the last strike and resets itself if another one lands. You still follow your governing body’s wait; Flash runs the clock and records when the all-clear went out.
Frequently asked
Half of it is. Current NFHS, NATA and NOAA guidance says to go inside as soon as you hear thunder or see lightning, not after a 30-second count. The 30-minute wait after the last thunder or lightning is still the standard for resuming play.
About 6 miles. Sound covers roughly a mile every 5 seconds, so divide the seconds by 5. Lightning can strike about 10 miles from a storm, so a 30-second gap means you are already within range.
Yes. NFHS and NATA both say any new thunder or nearby lightning after the count begins restarts the full 30 minutes.
No. NFHS says what you see and hear takes precedence over an app or device. Prediction moves the decision to clear the field earlier; it does not shorten the all-clear wait your policy sets.