Lightning is one of the most dangerous parts of a thunderstorm but often is not respected as that. Lightning forms as the result of particles of water and ice collisions in clouds. One charge develops in the clouds, the other builds up along the ground. These two charges build invisibly to each other, and when they meet, a lightning bolt occurs. This powerful surge of electricity is very dangerous.
The safest place to be in a thunderstorm is inside a building. When in a building avoid wires and plumbing. If you can’t get into a building, go inside a car or vehicle. It is a myth that the rubber tires protect you, but the current will flow on the outside frame of the car and will leave you safe on the inside.
The time to take action for lightning is when thunder is first heard. If you hear thunder that means you are within 10 to 12 miles of a lightning strike. Given that lightning can come from any rain of a thunderstorm. This means your threat is as great, and arguably can be greater, than if you saw a lightning strike close by.
The number of lightning deaths in Pennsylvania from the years 1990-2003 is 25. This ranks Pennsylvania at #6 with the most deaths in the United States. Florida is #1 at 126 deaths per year.
You should wait 30 minutes after hearing the last thunder to return to outdoor activities.