On Sep 1, 8:43*pm, wrote:
Not unreasonable to think that hills/mtns, buildings, tree lines and obstacles present a similar phenomenon from surface winds.

I'm catching up on this thread; but in case no one has mentioned it
yet: Surface objects (such as buildings, trees, small hills, etc) can
create turbulence downwind to a distance of 10-20 times their height.
When I flew R/C models this was *very* noticeable!

For example, a small stand of trees 100 feet high can cause turbulence
1/4 to 1/2 mile downwind of the trees. That seems like quite a ways
off (horizontally) if you're down low and scratching, so you may not
think about such objects. But they can have a profound impact on the
air you run into when you're making a save. And as John Sullivan
noted, that air is already quite "confused"!

--Noel