Originally Posted by Weevie
Why left in particular?
I can't remember all the specifics, but when I took my exams to obtain my Pilots Licence, we were taught that if the wind was coming from the North (360 deg on the compass) so Northerly @ 2000ft, As it got closer to the surface the friction, obstacles and I think also coriolis effect would slow the wind down and back it off a few degrees so at the surface, the same wind would be perhaps 335 deg. Perhaps instead of saying LEFT, I would have been more accurate if I'd said Anti-Clockwise.
This link seems to explain it: http://www.windwisdom.net/tutor2.htm
All the best