What does a 30 percent chance of rain mean?

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Dear Tom,
What does a 30 percent chance of rain mean?

Ron Roth

Dear Ron,
It can have two different meanings depending on the weather situation, but it always means one specific thing: There is a three in ten chance that rain will fall exactly where you are. The forecast of a 30 percent chance of rain can mean all of the area will get rain if it rains, but the forecaster has only a 30 percent confidence that rain will indeed arrive. It can also mean that scattered rain is a certainty, but it will affect only 30 percent of the area.

However, it’s not necessary that you know the forecaster’s intent because the meaning to you is always the same: A 30 percent chance of rain indicates that the forecaster believes the chance that you will experience rain is 30 percent, or three chances in ten.