1. Yes, they mean the same thing, practically speaking.
2. When we say "the forecast is/was for clear skies/rain/etc.," it means: "the forecast is predicting ..." [whatever type of weather it happens to be].
The meaning of "for" in this sentence is not isolated from the rest of the phrase. There is, however, one meaning of "for" which is similar to its import in this phrase, i.e., "in favor of." But I think most native English speakers would not mentally separate its meaning from the phrase as a whole.
Thanks. I have looked through many dictionaries (www.onelook.com) for the meaning of "for" but can't find a suitable definition except one or two mentioning "as a result." It is crazy to separate its meaning from the main body, but take it as a mental exercise. Thanks again. bmo