Velodrome atmospheric conditions During the Olympics the commentators made a big deal about the need to maintain very specific atmospheric conditions in the velodrome, including having airlocks to enter and exit the building.  

They stated that the atmosphere is very warm, and humid.  

Why are those precise conditions needed for velodrome events?  

My suspicion is the high temperature lowers the air density and thus lowers wind resistance but that's purely a guess.  I've no idea what the humidity levels would do to help, surely that would increase the air density again! 

Also, with such high temperatures, is there a danger of athletes overheating?
The equation for total aerodynamic drag force on a bicycle is well-understood and, you're right, air density has a role in it: the higher the density, the greater the drag. As you guessed, density decreases with increasing temperature so warm air is less dense than cold air. It's also probably no surprise that density decreases with pressure. However, evidently counter-intuitively, humid air is less dense than dry air. The simplest explanation is that water molecules contain two hydrogen atoms and one oxygen atom so they have a molecular mass of 18 g/mol, while dry air has a molecular mass of around 29 g/mol. You can check the wikipedia page on air density for more details.