The RH is pretty low up there anyway.
What's an RH?
Edit: I hate it when people post on forums with abbreviations that aren't in common use (in my opinion) that readers are expected to know.
As ian says, Relative Humidity.
The amount of moisture in the air as a percentage of the maximum it can hold at that temperature.
Simple explanation:
Air can hold a certain amount of moisture.
The amount it can contain depends on the temperature.
Warm air can hold more moisture than cool air.
If the RH is low, then the air is not saturated, and can easily hold more moisture, and things can dry out.
If the RH is very high then the air is saturated, and can't hold any more moisture and things won't dry.
For any given RH, then increasing the temperature will lower it, since for the same moisture content, the air can now hold more.
Dropping the temperature will increase the RH, since for the same moisture content, the air can now hold less.
If you drop the temperature enough, RH gets to 100% then the air can no longer hold the moisture that it already has has in it.
You have hit the Dew Point, and the water drops out and condenses on the cool surfaces.
This is what you see on the cisterns of unheated toilets, where there is condensation up to the cool water level.
And when you see mist down in a river valley, but it's clear higher up: Cool air has tumbled down into the valley, and the mist level is where the temperature profile has hit the dew point, and the cooler air lower down can't hold the same moisture so it drops out as vapour making clouds / mist / fog.