If you look at those three items they all affect corrected altitude which is how a blown injected motor is tuned for correct mixture. Bottom line on the humidity is you cant burn water so horsepower decreses when you are in a humid enviornment (race tracks in So. Carolina and Texas come to mind) so you are able to put more air in via the blower pulley change. You can also step on the timing and static compression as detenation is reduced from the water being in the air.
Barometric pressure tells you how much air is in that cubic foot of space that you are trying to put in the motor. The motor is just an air pump and loves more air.
Static temperature has an affect on the amount of air in that cubic foot also. The colder that air is the more you actually have in that cubic foot of space. NHRA loves Reading Penn as that place sometimes is called a mineshaft due to the fact of below sea level conditions(lots of air). Then on the other side there is Denver (less air). Its all about corrected altitude.