Adiabatic effects?
Does the different adiabatic behaviour of the water vapour also affect lift?
A wing flies because it generates increased pressure underneath as well as decreased pressure above.
If the wing lower surface meets the air, the air is compressed. Adiabatic compression would mean that the air underneath the wing must be warmer than the free air ahead.
Now water vapour has greater heat capacity than nitrogen and oxygen - it has an extra degree of freedom for rotation. Plus more vibrations allowed.
So, moist air does not warm as much as dry air when compressed - and therefore does not create as much extra pressure.
Analogically, moist air cooling above the wing should have higher temperature and higher pressure than dry air.
Is this a significant issue?