A 30% chance of rain means there is a 30% probability that measurable precipitation (at least 0.01 inch or 0.25 mm) will occur at a given location during the specified time period. In other words, there is about a one in three chance it will rain where you are
. This percentage does not mean:
- It will rain for 30% of the day.
- It will rain over 30% of the area.
- Any particular spot has exactly a 30% chance of rain.
Instead, the probability of precipitation (POP) is calculated as the forecaster’s confidence that rain will occur multiplied by the fraction of the area expected to receive rain. For example, if a forecaster is 50% confident that 60% of the area will get rain, the POP would be 30% (0.5 × 0.6 = 0.3)
. So, a 30% chance of rain means there is a moderate likelihood of rain somewhere in the forecast area during the time period, but it might not rain everywhere or for very long
