Multi777gamer

My 2008 Mac Pro running X-Plane 9.70 is giving me issues. At any airport when I't taking off or on approach the visibility reduces to the lowest setting possible. (I have real weather on). On Vatsim and just single player it happens. Its getting annoying. On Vatsim the other day I'm on a straight in approach for runway 28 on Vatsim at KORD. I'm on the visual its a sunny day with a few scattered clouds. Suddenly visibility reduces to nothing and I do a missed approach or quickly do the ILS. I live right next to KORD and it was still sunny. I know its good practice but its unrealistic. Any help? I will post specs if needed.

How about just FSX alone?

There are specs or my 2008 Mac Pro running OS X Yosemite 2 x 2.8 GHz Quad Core Intel Xeon 16GB 667MHz DDR2 FB-DIMM Nvida GeForce 8800 GT 512mb So I was wondering if my Mac Pro would run FSX with the PMDG 777 at 20+fps at descent settings using windows 7 home bootcamp. Thanks!