Very good, Pace.
And if there's no cloud or medium to high level cloud? If you don't know the dewpoint? (which you won't if you don't have a met observer's station at your airfield). And then you guess at the lapse rate? Go get the compass out of an aircraft to check the cloud movement direction? Eyeball the speed of cloud whose altitude you've only guessed at and end up with parallax errors? Or run after a cloud to time it over a known distance?
Gordon Bennet.
I think it might me just a
little easier to start from known wind on the ground, use a recognised rule of thumb (as already posted) and work out the 2000' wind from there.