Dry Thunderstorms & the 30/30 Rule

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Most of us are familiar with dry thunderstorms – they are defined as thunderstorms that produce little, if any rainfall at all. Typically the rain produced from these storms will evaporate before reaching the ground, simply because the air around Southern Oregon is so dry.

With dry thunderstorms comes dry lightning – a term which refers to lightning strikes occurring without significant amounts of rainfall. Even if a thunderstorm is producing rain …even heavy rain, lightning can strike as far as 10 miles away from the center of the storm.

Using thunder & lightning, we can calculate our distance from thunderstorms. After seeing lightning, count the number of seconds until you hear the thunder. Take this number and divide by 5. The number you are left with is the number of miles away the storm is.

If you count 30 seconds or less between lightning & thunder, lightning is close enough to pose a threat & you should go indoors. Once the storm passes, wait 30 minutes before going back outside. This is known as the 30/30 rule; most don’t realize that if you can hear thunder, you are close enough to be struck by lightning.

And another tip, heat lightning (often seen at night) is mistakenly believed to be generated from heat. This is false — heat lightning is simply lightning from a thunderstorm that is too far away to hear the thunder.