Where does the iPhone Weather app get its data from?

Who makes the forecasts for Apple's Weather app?

The iOS Weather app used to be powered by Yahoo Weather but changed to The Weather Channel with iOS 8. The Weather Channel bases its forecasts on its own meteorologists' interpretations of data from a variety of sources including the National Weather Service, NASA, satellites and weather balloons among others.

Where does the iPad / iPhone's Weather app get its forecasts from?