Lightning can strike as far as 10 miles away from the rain area in a thunderstorm. That’s about the distance you can hear thunder. When a storm is 10 miles away, it may even be difficult to tell a storm is coming.
IF YOU CAN HEAR THUNDER, YOU ARE WITHIN STRIKING DISTANCE. SEEK SAFE SHELTER IMMEDIATELY!
Use the 30-30 rule where visibility is good and there is nothing obstructing your view of the thunderstorm. When you see lightning, count the time until you hear thunder. If that time is 30 seconds or less, the thunderstorm is within 6 miles of you and is dangerous. Seek shelter immediately. The threat of lightning continues for much longer period than most people realize. Wait at least 30 minutes after the last clap of thunder before leaving shelter. Don’t be fooled by sunshine or blue sky!
Lightning research has confirmed that consecutive lightning strikes can occur as much as six miles apart. People often do not perceive lightning to be close if it is two miles or more away, but the risk of the next strike being at your location may actually be very high. Many lightning casualties occur in the beginning as a thunderstorm approaches because people ignore these precursors. When thunderstorms are in the area but not overhead, the lightning threat can exist even if it is sunny at your location. can exist even if it is sunny at your location.
Practice the ‘30/30′ rule and be lightning safe !
(Birmingham National Weather Service)