Lou, quick summary:
higher elevation, higher air temperature, lower barometric pressure, higher humidity = air that is less dense
lower elevation, lower air temperature, lower barometric pressure, lower humidity = air that is more dense
The golf ball travels further in air that is less dense. You'll notice it a lot if you play in Denver versus sea level, you'll notice it in the difference between 90* and 50*, if you pay close attention you can tell the difference between playing under a low pressure and a high pressure weather system, but you won't tell the difference humidity makes because its just a couple yards off the driver between the driest and wettest air you'll find at a given location.
If you want to play with various elevations, temperatures, etc. to see how they compare here's a link below. This doesn't translate directly into changes in distance but you can at least see the magnitude of the change. For instance I plugged in the numbers for the round I played on Saturday. I'm at about 700 ft here and the temp was 61, the dewpoint 34 and the pressure 29.95. No, I didn't memorize this, I know a site that shows the hourly conditions here for the last few days
It shows a relative density of 96.97%. That's relative to standard sea level, which is defined as 59*, 29.92", and 0% humidity....though 57* temp and dewpoint with 30" barometric pressure comes out to -20 ft and probably more closely approximates an cool day at Pebble Beach or TOC.
Now if I took a warm summer day here with a bit of a low pressure system moving through, I might plug in 90*, 29.50", and a dewpoint of 72* and I get 89.75%, so the air is about 11% less dense on those days. I don't actually fly it 11% further on such a day than I do at TOC so like I said you can't calculate your distance but you can at least compare the magnitude of changes in conditions.
http://wahiduddin.net/calc/calc_da.htm