Turn 10 have commented that it’s very unlikely night races and weather effects will be in Forza Motorsport 5.
Creative Director Dan Greenawalt explained to IGN that building the tracks on Forza Motorsport 5 was time consuming and that adding night and weather effects is not a “minor thing” to add. It won’t be easy to add such a thing in a patch he added.
Still, the Forza series itself has never has night racing or varying weather effects. These features may not be added in Forza Motorsport 5, but Turn 10 should consider them in the next game. Racing in the bright sun all of the time doesn’t always happen in real life…