Calculate how far away a lightning strike is using the flash-to-thunder delay. Includes a live timer, safety guidance, and risk assessment.
Press START when you see the flash, STOP when you hear thunder.
If thunder follows flash in under 30 seconds — seek shelter. Wait 30 minutes after the last thunder before going back outside.
Substantial building with plumbing and wiring. Stay away from windows and doors. Avoid contact with corded phones, water, and metal.
A metal-roofed vehicle is safe (not a convertible). Close windows. Don't touch metal surfaces inside. Lightning current flows around the shell.
Never shelter under a tree. Spread group out (not clustered). Crouch low with feet together on insulating mat. Stay off ridge lines.
Crouch low, feet together, hands over ears. Do NOT lie flat. Never stand under isolated trees. Move away from hills and high points.
Exit water immediately at any sign of a storm. Lightning can travel long distances through water. Wait until 30 minutes after last thunder.