Temperature and altitude

[Kutscha]

http://www.auf.asn.au/metimages/lapseprofile.gif

Found this posted on another board in a thread (P51-D vs F4U-4 & P38-L) in response when someone said:

"The only problem with the "cold weather" theory about European operations is that at 25K feet, it is just as cold over the equator as it is over Europe. It's also just as cold over the south west Pacific ocean area at 25K feet as it is at 25K feet over Europe."

[Red Admiral]

Its nonsense. Above the tropopause the temperature is the same, but 25000ft is considerably below.

Moisture content would vary quite a bit and there's also seasonal variation to consider.