Here are some stats of Vietnam climate if you plan to include weather as it is in Vietnam. This month is the worst...

http://www.vietnamembassy.org.uk/climate.html

http://www.weatherbase.com/weather/weather.php3?s=2884&cityname=Hanoi-Ha-Noi-Vietnam&units=us

Hope this help

Now that is actually a pretty good idea. Thank you!

Rain rain and more rain LOL, having been in this part of the world at this time of the year its rain the heaviest rain I have ever seen followed by a little sunshine then rain again, lets line up and bring a good umbrella.
Make sure you pack your snorkel to just incase you take fire and end up with holes in the plexi glass don't want to drown in that expensive gold fish bowl now.

Adding to much weather though may impact on the smoothness of the game.

At least fog and overcast? Fog and overcast doesn't reduce impact?  Temperature will have impact only on helicopter limitations.

I like the idea of adding weather to our missions. I was on a mission the other night with the designer and he had added weather and it added another dimension to the mission. He had rain and winds, which made landings into LZ's tricky...very real world.

FYI, I tried fog 6000m visibility and 1000m height. Give a really nice and real looking. I don't know if in DCS fog only mask some land and trees, but I know in certain game (ex x-Plane) is used free up GPU calculation, so increase FPS.

thanks ! very useful