Sound is absolutely different depending on the day. Humidity affects how frequencies travel through air. Joe Barresi said on Pensado's Place that if you're in the studio and everything sounds like shit that day, maybe don't record your vocals.
We had an SUV when I lived in the high desert, and the stereo system sounded harsh no matter what I did. When we moved cross country to a very humid state, one of the first things I noticed as we entered the area was that the car stereo all of a sudden sounded great. It made me want to go make albums in the desert; I thought, "if it sounds good there, it'll sound even better everywhere else."
All sound is is the disruption of air. When air changes, sound does too!