SA is a little different case. I think it starts at some time in autumn, or, even in July, which we're in. I think it could have taken months for Carl to go to SF and then LV, and have a fly to LC. When you start the game, everybody mentions that everything has changed, and Carl has forgot many things about the city of Los Santos. He's in LS, for at least 1 month, and then moves to SF. But there's a lot of business there and he doesn't go there just to rest for two nights.
It's logical that when he flies to LC, it's about October, and LS riots happen in December. I know it's not likely to snow in New York in October, but GTA also isn't a very realist game.
To complicate things further, SA's story was originally planned for 3 different characters like V (technological limits caused to not to stick with it) - so the stories could have easily happened simultaneously. One character per city, one story per character, but one timeline shared between them all - events happening in each story could have had a ripple effect on the next character, etc.
I don't see why the LC visit has to be so late in the year. It's based on NY and NY will snow any chance it gets. That could be anywhere from late Autumn to April, perhaps.
Also, we could easily consider that GTA's universe doesn't work by normal year lengths or weather patterns. That makes the most sense overall