"The weather is better in the south."
Translation:Il tempo è migliore al sud.
"Meglio" is an adverb while "migliore" is an adjective. In this case we use "migliore" because we want to define how "il tempo" is, not how "è/essere" is, even if actually we can also say "il tempo è meglio al sud" modifying the meaning of the verb. Eg "Let's find a better way" vs "You are better than me" :)
It seems to me that the correct verb is neither "è" nor "fa" but "sta". Why? Because we are talking neither about existence nor about production, instead we are reporting a state of being. We are saying that the weather is now in this state relative to location, not that it exists or that it is doing something. DL's translation looks weak to me.