Thunder and lightning are very dangerous. According to the National Weather Service “if you can hear thunder, you are within striking distance and you should seek shelter immediately.”
Lightning can strike up to 10 miles away from the rain area in a thunderstorm. The first stroke of lightning is just as deadly as the last. If they sky looks threatening, you should take shelter even if you don’t hear thunder.
Another tip from the National Weather Service is to use a “30-30 rule” where visibility is good and there is nothing obstructing your view of thunderstorms. When you see the 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. It is also recommended that you wait at least 30 minutes after a thunderstorm before returning to the outdoors, as the threat of lightning can continue long after a storm subsides.