Probability_of_precipitation
Probability of precipitation
Estimated likelihood of precipitation occurring within a specified forecast region
Probability of precipitation (PoP) is a commonly used term referring to the likelihood of precipitation falling in a particular area over a defined period of time, which is commonly a day, half day, or hour.
The PoP measure is meaningless unless it is associated with an interval of time. Forecasts commonly use PoP defined over 12-hour periods (PoP12), though 6-hour periods (PoP6) and other measures are also published. A "daytime" PoP12 means from 6 am to 6 pm.[1]
PoPs are generally not statistically independent. A good example of an event that has a strongly dependent hour-to-hour PoP is a hurricane. In that case, there may be a 1 in 5 chance of the hurricane hitting a given stretch of coast, but if it does arrive there will be rain for several hours, with the effect that a one-hour PoP for the same region and period would be similar: about 1 in 5. Localized thunderstorms may be less dependent, with the effect that the one-hour PoPs may be somewhat less than the one-day PoP.[2]