Lightning

The National Weather Service (NWS) is blunt: no place outdoors is safe during a thunderstorm. Lightning can strike more than 10 miles (16 km) from where it is raining. If you hear thunder, you are within range.

The 30-30 rule and what the NWS says today

The 30-30 rule had two parts: (1) if less than 30 seconds pass between the lightning and the thunder, seek shelter; (2) wait 30 minutes after the last thunder before going out. Today the NWS simplifies the first part: any thunder you hear means get to safety immediately, without counting seconds. The second part still stands: stay sheltered at least 30 minutes after the last thunder.

To estimate how far away the storm is: count the seconds between the lightning and the thunder and divide by 5 to get miles (by 3 for kilometers). Use it to see whether it is approaching, not to decide whether you are safe.

Shelters that work: a large building with electrical wiring or plumbing, or an enclosed vehicle with a metal roof and the windows up. Shelters that do not: tents, open pavilions, shallow caves, rock overhangs, convertibles.

If you are caught in the backcountry with no shelter

None of these measures makes you safe; they only reduce the risk a little. Plan to be off summits and ridges before noon during storm season.

1. Get down immediately from summits, ridges, hills, and high ground.
2. Get away from water: get out of lakes, ponds, and rivers, and off their banks.
3. Do not shelter under an isolated tree or under rock overhangs or at cave entrances.
4. In the forest, get as far as possible from any single tree; do not huddle against the trunk.
5. Stay away from wire fences, power lines, windmills and any long metal object.
6. Never lie down on the ground. The current travels along the surface.
7. In a group, spread out so a single strike does not injure everyone and survivors remain to give first aid.