What does 30 percent chance of rain mean?
CHICOPEE, Mass. Well, the technical term Meteorologists use for rain chances is Probability of Precipitation, or POP for short. It takes into account two different factors. The first is percent confidence. The second is percent coverage. The POP is equal to the percent confidence multiplied by the percent coverage. POP = Percent Confidence x Percent Coverage  Yes, it is an actual mathematical equation! For example, a 30 percent chance of rain may mean 100 percent confidence that only 30 percent of the forecast area is going to get rain. Days like that, we say isolated showers. You can also get a roughly 30 percent POP with 80 percent confidence that 40 percent of the forecast area will get rain, and so on and so forth. Anything at or above a 30 percent chance of rain, its always a good idea to make sure you have my umbrella with you.