HOW CLOSE WAS THAT?

If If you’re you’re on on a a hilltop hilltop or or ridgeline, ridgeline, head head downhill downhill as as soon soon as as you you hear hear distant distant rumbles. rumbles.

Most of us learned as kids to estimate how far away a lightning strike occurred by counting the interval between the “flash” and the “bang”: Because light travels so much faster than sound, you’ll see a distant flash before you’ll hear the sound of the thunder. Sound travels roughly one mile every five seconds, so counting the seconds between the flash and the bang, then dividing by five, tells you roughly how far off the storm is.

There are serious limitations to this method, however. For one thing, in heavy storms it can be difficult to distinguish which “flashes” go with which “bangs.” And weather conditions can affect your ability to hear. In calm conditions, you can hear thunder about 10 miles away; during a hard, windy rain, you might be lucky to hear a strike one mile away.

A simpler method is the “30-30 rule.” A lightning bolt can strike as far as six to eight miles away from the previous strike. If at any time you count less than 30 seconds between the flash and the bang, you are within range of the next strike. (The other part of the 30-30 rule has to do with the time before and after the storm. Most deaths from lightning occur either 30 minutes before or 30 minutes after a storm passes, when people underestimate the risk of being struck and fail to take cover.)

Counting the time between flashes and bangs might be able to give you some information about whether a storm is moving toward or away from you, but it’s not worth risking your life on. If you can hear thunder or see lightning at all, it’s best to take cover.