Objective
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Clarify which one to use 'Futuro' or 'Subjuntivo' (or it does not matter) to say "I do not believe/think it will rain tomorrow".

* No creo que lloverá mañana.
* No creo que llueva mañana.

In my understanding, 'Futuro' to talk about the future possibility and 'subjunctive' to talk about the belief/understanding/opinion in negation. When a sentence has both, which one to use and are there implications that the talker intends?