The info comes from the japanese Xbox site, as far as I'm aware weather and nighttime racing have been on top of the Forza wishlist for a long time:

As real as it gets

Breathtaking graphics at 1080px resolution and 50 frames per second. Wet weather, 3D puddles, and night racing test your driving skills. Cutting-edge ForzaTech™ engine powers the unrelenting action and stat-of-the-art-physics at simulation speed.

Ultimate car fantasy

The most cars of any racing game this generation. More than 450 cars all immaculately recreated and customizable, and complete with working cockpits and full damage. Tour 26 world-famous locales including Daytone, Rio, and more..

Never race alone

Home of the greatest racing, tuning and painting community in gaming. 2-player split-screen racing, 24-player races, and realistic Drivatar opponents deliver packed tracks and unrivaled action.

http://www.xbox.com/ja-JP/games/forza-6/6_15/9d32baa8-7b67-4f7e-be5b-79cc868573bc

The graphics look amazing. 50fps sounds wrong. Nighttime racing and weather are good additions but 5 years late but definitely welcome additions to the series.

1080px? Is that a typo?

Game is looking good. Not sure if I will purchase it though.

50 fps? I dont get it. Why not 60 fps?

It comes from the Japanese store so it got translation errors like the 1080xp and 50fps. I assume it is 60 FPS , well we see soon.

Probably, the 50fps thing might be a typo as well.

So they're finally making a racing sim.

50 fps might be a typo but I'm pretty sure it's not a translation error, how would you mistranslate 60 as 50? :D

50fps seems enough. Didn't a developer say in an interview that human eye cannot see past 30fps? XD

Simple I meant to say 60 in Japanese but say 50.