forecast (v.)
late 14c., "to scheme," from fore- "before" + casten in the sense of "contrive, plan, prepare" (late 14c.; see cast (v.)). Meaning "predict events" first attested late 15c. (cast (v.) "to perceive, notice" is from late 14c.). Related: Forecasted; forecasting.
forecast (n.)
early 15c., probably from forecast (v.); earliest sense was "forethought, prudence;" meaning "conjectured estimate of a future course" is from 1670s. A Middle English word for weather forecasting was aeromancy.