National Weather Service Weather Forecast Office

The "30/30" Lightning Safety Rule

The "30/30" lightning safety rule is defined as the following:

1) It is strongly recommended that you should seek safe shelter when you first hear thunder, observe lightning or see dark threatening clouds developing overhead. You should already be in a safe location when the time between the lightning flash and the rumble of thunder is 30 seconds or less.

2) You should not resume activities until after 30 minutes after the last audible thunder.

Click here to calculate how far lightning is away from you

An important thing to remember: Sometimes lightning storms can develop overhead. This means that the first lightning strike from the cloud might be in your immediate location. It is recommended that you should be alert for developing thunderclouds overhead when outdoors. If you see thunderclouds developing or darkening skies overhead, you should implement your lightning safety plan of action.

In addition, there are times when a lightning flash can travel horizontally many miles away from the thunderstorm cloud itself and then strike the ground. These types of lightning flashes are called "Bolts from the Blue" The reason why they are called "Bolts from the Blue" is because they appear to come out of a clear blue sky. Although these flashes are very, very infrequent, they have been known to cause fatalities. Click here form more information about "Bolts from the Blue".

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Go to NOAA/NWS Outdoor Lightning Safety - When a Safe Location is Nearby

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