http://www.conjuga-me.net/verbo-chover. When you have the First Conditional in English, the verb in the "situation clause" is in future subjunctive in Portuguese. "Se você viajar..." / "se nós encontrarmos..."
Ah I see :). According to the conjugation table it is in fact the future subjunctive, correct? Would it also be (perhaps somewhat) possible to use the present conjunctive in this case? -> Se não chova, eu vou ao colégio.