Thunderstorms can produce lightning, heavy rain, strong winds, hail, and flash flooding, so knowing what to do before one arrives can prevent injuries. Lightning is especially dangerous because it can strike several miles away from the center of a storm. A safe response plan helps students move quickly from risky outdoor areas to safer shelter.
Preparedness also reduces panic because everyone knows where to go and what to avoid.
Lightning forms when electric charges separate inside storm clouds and create a strong electric field between clouds, the ground, or different parts of the cloud. When the electric field becomes strong enough, a fast electrical discharge heats the air and creates the bright flash and thunder that follows. The safest place during a thunderstorm is a substantial building with wiring and plumbing, or a hard-topped vehicle with the windows closed.
After the storm seems to pass, wait at least 30 minutes after the last thunder before returning outdoors.
Key Facts
- If you hear thunder, lightning is close enough to be dangerous.
- Use the 30-30 rule: go indoors if thunder follows lightning within 30 seconds, and stay indoors for 30 minutes after the last thunder.
- Distance to lightning in miles is approximately time between flash and thunder in seconds divided by 5.
- Speed of sound in air is about 343 m/s, so thunder arrives after the lightning flash.
- A safe shelter is a substantial building or a fully enclosed hard-topped vehicle, not a tree, tent, dugout, or picnic shelter.
- Avoid corded phones, wired electronics, plumbing, windows, and metal objects during a thunderstorm.
Vocabulary
- Thunderstorm
- A thunderstorm is a storm with lightning and thunder, often including heavy rain, strong wind, or hail.
- Lightning
- Lightning is a sudden electrical discharge caused by separated electric charges in a storm cloud or between a cloud and the ground.
- Thunder
- Thunder is the sound produced when lightning rapidly heats the air and the air expands explosively.
- Flash Flood
- A flash flood is a rapid rise of water that can occur during or after heavy rain, especially in low areas, streets, and drainage channels.
- Safe Shelter
- A safe shelter is a substantial enclosed building or hard-topped vehicle that helps protect people from lightning, wind, and flying debris.
Common Mistakes to Avoid
- Standing under a tree for cover is unsafe because lightning can strike the tree and travel through the trunk, ground, or nearby air.
- Waiting until rain starts before going inside is dangerous because lightning can strike before rain reaches your location.
- Using wired electronics or plumbing indoors is risky because lightning energy can travel through electrical wiring, phone lines, and pipes.
- Returning outside right after the rain stops is unsafe because lightning can still strike from the remaining storm clouds.
Practice Questions
- 1 You see lightning and hear thunder 15 seconds later. About how many miles away is the lightning, and should you go indoors according to the 30-30 rule?
- 2 A soccer team hears the last thunder at 4:12 p.m. Using the safety rule, what is the earliest time they should return to the field?
- 3 A student is caught outside during a thunderstorm near a tall tree, a metal fence, a small open picnic shelter, and a school building 100 meters away. Explain which option is safest and why.