The RAINcast map shows forecast precipitation for the next 48 hours at 3 hour intervals. Each color-coded map shows predicted accumulation measured in hundredths of inches. Where the precipitation falls as snow, the amount of liquid equivalent of the melted snow would be depicted on these maps.

Rain is a type of precipitation, a product of the condensation of atmospheric water vapor that is deposited on the Earth's surface. It forms when separate drops of water fall to the Earth from clouds. Not all rain reaches the surface; some evaporates while falling through dry air. When none of it reaches the ground, it is called virga, a phenomenon often seen in hot, dry desert regions.

Rain plays a role in the water cycle in which moisture from the oceans evaporates, condenses into drops, precipitates (falls) from the sky, and eventually returns to the ocean via rivers and streams to repeat the cycle again. The water vapor from plant respiration also contributes to the moisture in the atmosphere.

A major scientific explanation of how rain forms and falls is called the Bergeron process. More recent research points to the influence of Cloud condensation nuclei released as the result of biological processes.