In most cases, clear blue sunny sky. Convective (Thunderstorm) clouds can build up as high at 50,000ft but this is unusual. Temperatures above 18,000ft are almost always below freezing so the chance...
No. Cirrus clouds are very high clouds, and as a result, are composed almost entirely of ice. The suspended ice particles, though of course subject to the effects of gravity, remain aloft due to the...