The "percent chance of rain," also known as Probability of Precipitation (PoP), represents the likelihood that measurable rain (at least 0.01 inches) will fall at any given point in the forecast area during a specified time period, such as a day or part of a day
. Key points to understand about this percentage:
- It does not mean that it will rain for that percentage of the time, nor that that percentage of the area will definitely get rain
- Instead, it means there is that percentage chance that rain will occur at any single point in the forecast area during the specified time
- The forecast is based on a combination of forecaster confidence and the expected areal coverage of precipitation. For example, a 40% chance could mean the forecaster is 80% confident it will rain, but expects it to cover only 50% of the area, or vice versa
- Meteorologists often derive this probability from ensemble forecasts-multiple model simulations-and the percentage reflects how many of those simulations predict rain
- For instance, a 30% chance of rain means that on days with similar weather conditions, rain occurred in about 30% of those cases
- An 80% chance means there is a high likelihood that at least some measurable rain will fall somewhere in the forecast area during the time period
In summary, the percent chance of rain is a statistical estimate of the probability that measurable precipitation will occur at a given location within the forecast area during the stated time frame, rather than a measure of how long or how much of the area will be wet
