The PRECIPcast map shows the probability of precipitation for the current day and the next 24 hours at 6 hour intervals. The types of precipitation shown on the map include rain and snow. The maps for each interval are available within the drop-down menu.

In meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena) is any product of the condensation of atmospheric water vapor that is deposited on the earth's surface. It occurs when the atmosphere (being a large gaseous solution) becomes saturated with water vapor and the water condenses and falls out of solution (i.e., precipitates). Air becomes saturated via two processes, cooling and adding moisture.

Precipitation that reaches the surface of the earth can occur in many different forms, including rain, freezing rain, drizzle, snow, ice pellets, and hail. Virga is precipitation that begins falling to the earth but evaporates before reaching the surface. Precipitation is a major component of the water cycle, and is responsible for depositing most of the fresh water on the planet. Approximately 505,000 km³ of water falls as precipitation each year, 398,000 km³ of it over the oceans. Given the Earth's surface area, that means the globally-averaged annual precipitation is about 1 m, and the average annual precipitation over oceans is about 1.1 m.