I have this game call TestDrive2 (TDU2) or Burnout Paradise City (BOPC) and it really cool how you can play in the day time and any minute it goes to night time in BOPC you can change settings to simulate 24hr days and in TDU2 it rains occasion which affects driving enviroment.
This effect would be ultimate add-on which is a true scenario and maybe add snow or wind to give it and added feel.
P.S. I like Hidden and Dangerous and always thought military games should be like that but now i have found Arma... really cool keep up the good work.