Determining how long after thunder it is safe to go outside is an important consideration when a thunderstorm is in the area. Thunder and lightning can be very dangerous, so it’s crucial to wait a sufficient amount of time before resuming normal outdoor activities.
The 30/30 Rule
Experts often recommend using the 30/30 rule to determine if it is safe to go outside after thunder. This rule states that you should wait 30 minutes after hearing the last thunder before going outside. In addition, after hearing the last thunder, you should wait until 30 minutes have passed without hearing more thunder before going outside.
Why 30 minutes? Thunder can travel up to 10 miles from its lightning strike, which takes about 5 seconds per mile. So waiting 30 minutes allows a safe buffer of time to ensure the thunderstorm is sufficiently far away.
Other Safety Recommendations
In addition to the 30/30 rule, other recommendations for staying safe after thunder include:
- Wait in a safe location like inside a building or a hard-topped metal vehicle. Avoid open fields, pavilions, or being near trees.
- Avoid using plumbing and electric equipment as lightning can travel through pipes and wiring.
- If you are caught outside during a storm, crouch down with your hands on your knees. Make yourself as small a target as possible and minimize contact with the ground.
- Get to safe shelter immediately if you hear thunder. Do not wait for the storm to get closer or directly overhead.
Special Cases
Certain situations may require taking extra precautions beyond the 30 minute recommendation:
- Outdoor events/gatherings: Event organizers should have a lightning safety plan and designated safe locations. Activities should stop at the first sign of lightning or thunder.
- Beaches and open water: Get out of the water immediately and seek shelter away from the beach. Water is an excellent conductor of electricity.
- Golf courses: Do not wait under trees or open shelters. Get inside a substantial building or hard-topped metal vehicle.
- Agriculture work: Get off riding machinery as quickly as possible. Crouch low if dismounting is not possible.
Know the Signs of a Coming Thunderstorm
Being aware of signs of an approaching thunderstorm can help you get to safety sooner:
- Darkening skies
- Distant rumbles of thunder
- Sudden wind shifts
- Rapid temperature drops
- Increasing humidity
Heading inside at the first sign of a thunderstorm ensures you won’t get caught outside when the lightning begins.
How to Estimate Distance from Lightning
If you can see lightning but can’t hear accompanying thunder yet, you can estimate the distance of the lightning strike. Light travels faster than sound, so there is a delay between seeing the lightning flash and hearing resulting thunder.
To estimate the distance in miles, count the number of seconds between the lightning flash and the thunder and then divide by 5. For example, a 30 second delay means the lightning is approximately 6 miles away (30/5=6).
Distance Estimation Table
| Seconds Between Lightning and Thunder | Approximate Distance (Miles) |
|---|---|
| 5 | 1 |
| 10 | 2 |
| 15 | 3 |
| 20 | 4 |
| 25 | 5 |
| 30 | 6 |
Conclusion
Lightning and thunder can be hazardous, so take proper safety precautions during a thunderstorm. Use the 30/30 rule as a minimum timeframe, staying indoors for 30 minutes after the last thunder. Additionally, don’t go back outdoors until 30 minutes of silence has elapsed after hearing the final thunder. Understanding lightning distance estimation can also help inform safety decisions if you get caught outside during a storm. Following these rules will help minimize the risks from one of nature’s most dangerous phenomena.