Is it ok to say " I heard on the weatherforecast that it will rain today". or do I say " I heard in...."?
British native not a teacher.
The preposition you need is 'on'. 'In' would be wrong in English. We always say 'on the radio, on the television'. Other languages such as German say 'in'. Prepositions are not always logical!
Weather forecast is two words.
Hope that helps