Count the seconds between the lightning flash and the thunder
Divide the number of seconds by 5 to estimate the distance in miles
Divide the number of seconds by 3 to estimate the distance in kilometers
Example: 10 seconds means about 2 miles away
Example: 10 seconds means about 3 kilometers away
If the time is less than 30 seconds, the storm is close
If thunder is immediate, the lightning is very close
Move to shelter if the storm is getting closer