Thunder is the sound created when lightning passes through the air, causing it to rapidly heat and cool, resulting in a massive pressure wave that can be heard. A single lightning bolt can raise the temperature of the air around it as high as 50,000 degrees Fahrenheit.
Using the sound of thunder, an observer can make an educated estimation of the distance from the lightning strike they are. This is because sound travels at a constant rate, and the sound of thunder travels at approximately one mile every five seconds. With this formula, anyone caught outside during a lightning storm can tell just how close the lightning is, and how urgently they need to move indoors. Suitable shelter should be sought any time lightning is striking in the immediate area due to the substantial threat it presents. Direct strikes can be lethal and indirect strikes can damage structures or start fires. Greater risk is present in areas which have tall structures or trees, or to those in and near bodies of water. If shelter can't be found inside a building taking cover inside a vehicle is the next best option as the rubber tires provide greater protection from the electrical current being discharged.