Barometric pressure in Philly 28.29 ??

[dumbledork]

15. Yes, it is (oddly) true that water is lighter than air (in its gaseous state), but

it still doesn't have anything to do with pressure. Suppose you take a hermetic vessel containing some air (or even pure N2 if you wish)...you can change its pressure with heating or cooling (Charles' Law) or by mechanical adiabatic compression/expansion (Boyle's)...the absolute humidity doesn't change, in
that essentially isentropic system. It is, all that being said, true that high pressure in the atmosphere is usually associated with low water vapor levels but that is dependent on lots of other factors including inversions.