According to Dictionary.com
forecast[fawr-kast, -kahst, fohr-]
verb (used with object), forecast or forecasted, forecasting.
to predict (a future condition or occurrence); calculate in advance
to forecast a heavy snowfall; to forecast lower interest rates.
to serve as a prediction of; foreshadow.
to contrive or plan beforehand; prearrange.
verb (used without object), forecast or forecasted, forecasting.
4.to conjecture beforehand; make a prediction.
5.to plan or arrange beforehand. noun
6.a prediction, especially as to the weather.
7.a conjecture as to something in the future.
8.the act, practice, or faculty of forecasting.
9.Archaic. foresight in planning.
According to Online Etymology dictionary, fore- has an etymology of Middle-English but Cast doesn't have a known origin. Forecast doesn't have a known origin either.
So what is the origin of the word forecast?