Guys, i'm not really sure if humidity is implemented in DCS, but this is all dependent on relative humidity, temperature and more.. There is a Wikipedia article that explains this very well, I will link it in a while.
In real life, when humidity is low (among other conditions) you can see that at high AoA & G-force there could be barely, if any, any vapor on LEX.. In other times you could have vapor at level flight (1G), mainly happens with jets that operate on carriers at sea. So it is very variable in real life too.