A severe thunderstorm is expected to roll through the New York City area later this evening.  As it approaches and lightning begins to illuminate the sky, you can estimate how far away the storm is with some simple math.

Since lightning travels at approximately the speed of light – 186,000 miles per second – you see it almost instantly.  Thunder, on the other hand, travels at the speed of sound – about one mile in five seconds – at the Earth’s surface. These different rates of travel allow you to estimate the distance between yourself and the lightning.   For example, if you count fifteen seconds between seeing lightning flash in the sky and hearing a clap of thunder, the lightning is about three miles away.

Remember, if you can hear thunder, lightning is close enough to possibly strike. So, as NOAA recommends, “When thunder roars, go indoors.”

Cloud to ground lightning strike.

Image Credit: NOAA