What to do if you are caught outside in a thunderstorm

01

What is the first thing to do?[1]

Move toward a substantial building or a hard-topped metal vehicle and keep moving until you reach one. A substantial building means one with wiring and plumbing: a house, a shop, an office. Picnic shelters, dugouts, bus stops and tents do not count.

The distinction between a building and a shelter is the part people get wrong. A roof keeps rain off, which is what makes an open picnic shelter feel like safety. It does nothing about lightning, because there is no conductive path around you and no grounding system. Standing under one puts you beside tall posts in an open area.

Distance matters less than direction. If the nearest real building is 10 minutes away, start walking. The advice to stop and crouch was built on the idea that the walk itself was the danger, and the evidence did not support that.

02

Should you crouch down if you cannot find shelter?[2]

No. The National Weather Service dropped the lightning crouch from its guidance because it does not measurably reduce your risk. Crouching leaves you exposed to ground current, which causes the most lightning deaths and injuries. Keep moving toward a real building instead.

The crouch was taught for decades, so it still turns up in older first aid courses and scout handbooks. The reasoning was that minimising your height and your contact with the ground would help. In practice ground current spreads outward through the soil from the strike point, and a crouching person is still standing on that soil.

What replaced the crouch is less satisfying but more honest: there is no posture that makes open ground safe. The advice is now to treat every minute outside as risk you are trying to end, rather than to adopt a position and wait it out.

03

What should you avoid while you move?[1][3]

Avoid being the tallest thing around, avoid isolated tall objects, and avoid anything that conducts. Height, pointed shape and isolation are what draw a strike, so a lone tree in a field is one of the worst places to stand.

One counterintuitive point: a forest is safer than a lone tree, because no single trunk stands out and the strike has many equally attractive targets. If you are in continuous woodland, move away from the tallest trees and the edges rather than trying to leave the trees entirely.

Isolated trees

Sheltering under one is the second leading cause of lightning casualties

Ridgelines and summits

You become the high point over a wide area. Descend before the storm arrives, not during it

Open water

Get off lakes and out of pools. A person in a boat or swimming is the tallest object on a flat surface

Metal fences and rails

Long conductors carry current far from the strike point, sometimes hundreds of meters

Tall poles and towers

Being near one is worse than being away from it, because of side flash

04

Why should groups spread out?[3]

Spreading out prevents one strike from injuring everyone at once. Ground current and side flash both affect an area rather than a point, so a cluster of people standing together can all be hurt by a single strike. Separation also leaves someone able to give first aid.

The usual recommendation is at least 20 meters between people. That is far enough that ground current has weakened noticeably, and far enough that a side flash jumping to one person is unlikely to reach the next.

The second reason is the one that gets overlooked. Lightning casualties often need immediate CPR, and cardiac arrest from a strike is survivable when someone starts compressions quickly. A group that spreads out is a group where somebody is still standing.

05

When is it safe to go back out?[1]

Thirty minutes after the last clap of thunder. Strikes can travel more than 10 miles from the storm's rain, so blue sky overhead is not the signal. Thunder is, and the clock restarts every time you hear it.

Most people are struck before or after the peak of a storm rather than in the middle of it. That is the practical case for the 30-minute rule: the dangerous windows are exactly the ones that feel safe, when the rain has stopped and the sky is brightening.