The air is defently heavier in humid conditions. Ive purposely gone out to the desert valleys in adverse conditions (high humidity) and started sending rounds out to 1K and found my poi falling short by about 1-1.5 moa @ 1K. 10 inches doesnt sound like much buts its the difference between a hit or a miss.
Ive shot the same rig out to the same distance in dry conditions and my rounds went where there supposed to go.
Frankly, Id much rather deal with wet air as opposed to dry "windy" air. Seems like the more i think I have my windage adjustments figured out, the more the Gods of wind send me back to school.