If you can hear thunder, or can see a stroke to the ground, you are within 10 to 15 miles, and in a high danger zone. You must have a safe location in mind and be ready to move to it quickly. If you are with a group, alert them to this threat and make sure everyone knows how to get to safety without delay. You can estimate the distance to lighting by watching for the flash and counting the number of seconds until thunder is heard. For every five seconds you count, the lighting is one mile away.
Scientists estimate that lightning can travel at around one mile per minute.
You need to allow plenty of time to get to safety. If you are with a large group that reacts slowly, the safety time required may be 10 to 15 minutes. But this is only an estimate, and if the lightning is extremely intense, bright and frequent, you should begin to move earlier. Lightning primarily tends to strike tall objects as well as metal objects, and can travel through moist soils for dozens of feet. To select the best shelter, move into a sturdy building and stay away from windows and doors.