It's easy to tell how far away a thunderstorm is. All you need is to be able to hear the thunder.
When you see the lightning start counting seconds (one mississippi, two mississippi...). If you happen to have a stopwatch with you, all the better! Stop counting when you hear the thunder. Now, take the number of seconds you counted and divide by 5. The result is the number of miles to the storm. Thunder travels at about 5 seconds per mile.
If you hear a lound snap followed immediately by either nothing or thunder, hide under your bed. The storm is exactly where you are standing. (Note interesting ozone smell.)
This method is based on a number of assumptions:
- The speed of light is estimated as infinite here.
- The speed of sound is estimated at 0.2 miles per second. (Yes, I know that sound is affected by heat and humidity, but why complicate things?)
Thunder can be heard up to 7 to 22 miles away, depending on the lay of the land.