Precipitation refers to water that falls from the sky, such as rain, drizzle, snow, sleet, hail, or something rarer. Precipitation is an important aspect of weather forecasting, and it can tell us about other things going on in the atmosphere, as well as what we might need to do, like taking an umbrella or getting ready to build a snowman. There are two ways to express the probability of precipitation in weather forecasts: as a percentage or as a probability of precipitation (PoP) .

When expressed as a percentage, the probability of precipitation tells us the likelihood of rain occurring in a given area and time period. For example, a 30% chance of rain means that there is a 30% chance that it will rain in the forecast area during the specified time period.

When expressed as a PoP, it describes the probability that the forecast point in question will receive at least 0.01 inches of rain. For example, a 40% chance of rain means that there is a 40% probability of at least 0.01 inches of rain at the specific forecast point of interest.

It is important to note that the probability of precipitation does not indicate the amount of rain that will fall, the duration of the rain, or the coverage area of the rain. It is simply a statistical probability of precipitation occurring in a given area and time period.