Parson, you'll note from my post that even with good planning and almost zero reported local surface wind, severe turbulence can still get you if you fly downwind of mountains.
And it can be more subtle than that. I was once doing a biennial check out of Liverpool (usually done with an aeros instructor in our Chippy, but I'd left it too late and was doing it in a PA38 from the Liverpool club). Not being aerobatic, I'd opted to spend the hour in the Tommy on instrument revision and the instructor (not having screens) put charts up to block the outside view.
At one point I had cruise power set, and cruise attitude. Speed was correct on the ASI but we were going down. I pointed this out to the instructor and he couldn't explain it. I moved the chart for a look upwind..... we were downwind of a considerable Welsh hill!
Sorry to continue the slight thread drift but I think it's worth saying...