I was wondering if there is some sort of standard that you can figure out the DA your flying in given the altitude your at if you know what the DA is on the ground. I guess I could get my books out and cook something up with adiabatic lapse rates and DA formulas or something. but is there a rule of thumb? I wanted to go direct out of KCTB to 32S but the DA on the ground was over 6K and I didn't figure I'd be going much over 9,500' and I was hearing PIREPS of strong mountain waves and that was cutting it a little close for me.. Next thing I know I'm at 12,500 (Couple of up drafts didn't hurt, but we stayed there and I was able to get it back after some down drafts) after filling up with 2 on board and 50lbs of gear so I hit the D-> and away we went. there was about a 2600' difference in DA vs Elevation at the airport so if it was linear that would have put me at 15,100' DA but It can't be linear. I suppose its possible to be flying at a lower DA than take off in some situations.