Why don't we use 会 here, like the other examples?
From what I understand you can use it, but since "明天" already clarifies that the event is occurring in the future, it isn't necessary.
Also wondering why 会 isn't needed here... Seems wrong.
I would suggest "Tomorrow will be a cloudy day"
I put 明天会是阴天 and was marked correct. 2/21/20
Ok saw it... Sorry.