But the dewpoint will change with height also...
Rule of thumb for cumulus clouds is that the base will be at 400x(difference between surface temp and surface dewpoint) in feet.
For 21C and 7C the difference is 14C. 400x14=5600. So you estimate the height of the cloud base will be 5600 feet. Answer D.
Edit: crossed with Prazum - and note we are saying the same thing.
Last edited by Heston; 14th May 2013 at 20:12.