How are rain chances determined?

KNOXVILLE, Tenn. (WVLT) - Teri Stern Taylor Huskey asked, "How do you determine the percentage of area that will see rain?"

You hear us say there's chance for rain/snow, or you see a percentage on the graphics. This is what we call a Probability of Precipitation, or PoP.

The PoP describes the chance of precipitation occurring at any point in the area.

Mathematically, PoP is defined as follows:

PoP = C x A

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

For example, there may be a high confidence in precipitation but only a small percentage of the area.

This is why glancing at the weather from the app on your phone or online, may not give you a good idea of what we're expecting. On-air we'll say scattered showers, a percentage-coverage of our area, and break down which parts of the day have better chances than others. This will help you better plan out your day!