"It may snow tomorrow."
Is 明天可能下雪 acceptable? I just wonder why do we need 会 here, since the sentence itself already indicates future at "明天" already, doesn't it?
It's not entirely necessary, but it's more grammatically correct. In real conversation it's common to leave out the 会 just for the sake of getting the point across faster, but including 会 is more specific and makes more sense and flows better. Duo probably wants you to inclhde the latter to teach you proper grammar. It's the difference between saying "It might snow tomorrow" and just "Might snow tomorrow". Both are understandable and neither are technically incorrect, but one is more proper whereas the other is more casual and conversational.
Native speaker here in conversational Chinese I never usually use 会 and would instead just say 明天可能下雪
I can't tell you why, but as far as i've seen, you truly do need to add 会 when using 可能 to talk about a 'maybe' in the future, even if you specify when in the future youre talking about.
Given that the translation for "It may rain on the weekend" does not require or suggest the use of 会, it should not be required here either. The weekend there is also clearly a future date.
Would the meaning change with 会可能 instead of 可能会? Or would that make it ungrammatical?
Because it is the only word used in the sentence that makes it something that will happen in the future. 可能 says maybe, not can (there is some doubt), and 会 adds the notion that it is something that will happen in the future, the next day in this case.