The first one is correct, because "is like" is describing the similarity between things. Also you could say, "These days the weather feels more like fall." Hopefully that makes sense.

These days the weather is like fall. So the first one is correct. In South Africa we call Fall, Autumn :) Hope this helps.

You're much more likely to hear "This is fall weather" or "Today feels like fall" than "These days the weather is like fall", which to me does not sound like natural English.

#2 is more correct than #1. But you might try one of these alternatives: * These days the weather is fall-like. * We're having fall weather these days.