## What is the Meaning of Probability of Precipitation?

Posted by Kyle Brookings on Sunday, August 20, 2017

Posted by Kyle Brookings on Sunday, August 20, 2017

First off, what is precipitation? Well precipitation is any form of water - liquid or solid - falling from the sky.

The "Probability of Precipitation" (PoP) describes the chance of precipitation occurring at any point in the forecast area.

So if there is a "40 percent" chance of rain, it means it will produce measurable precipitation over an area.

**Mathematically, PoP is defined as follows:**

- PoP = C x A where "C" = the confidence that precipitation will occur somewhere in the forecast area, and where "A" = the percent of the area that will receive measurable precipitation, if it occurs at all.

- So... in the case of the forecast above, if the forecaster knows precipitation is sure to occur ( confidence is 100% ), he/she is expressing how much of the area will receive measurable rain. ( PoP = "C" x "A" or "1" times ".4" which equals .4 or 40%.)

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