Not adding anything to the debate, other then to prove there are more answers than question on the web .. this is a different set of numbers from wiki-answers.
17 in. Hg: 188.07 °F or 86.71 °C (at approx 15,000 ft or 4572 m above SL)
10 in. Hg: 175.11 °F or 79.51 °C (at approx 27,000 ft or 8230 m above SL)
5 in. Hg: 165.85 °F or 74.36 °C (at approx 42,000 ft 12,802 m above SL)
Perhaps when I get a minute tomorrow I'll find the formaula and make an excel sheet .. if only for me own eddification. Then look up what latent heat of vaporisation has to do with it - and why it increases at altitude, when I would expect it to decrease with falling vapour pressure.
DGG
