Chris OCallaghan wrote:

Granted, our attention spans are short, but spending a half hour on
your back watching the development of a cumulus cloud can be very
instructive.

We've been talking about dust devils, which rotate as fast as 20 times
minute, but you seem to be talking about rotations slower than 10 times
per hour. No wonder I don't notice rotations like that while flying.

But you needn't even do this if you are observant during
your climbs. You will note that around the edges of the cloud you'll
occasionally see vortices forming when the light hits them right.

I do see these generally small clumps of rotations in the vertical
plane, near cloud edges. This isn't what I would call "clouds rotating"
in this context (which direction to circle), by which I mean a
substantial amount of the cloud going around horizontally like a dust
devil does. I have seen roll clouds rotating rapidly, but that isn't
relevant to dust devils.

Or
if there is clag below cloud base, it will often have a discernable
rotation. When observed, they often herald localized cores that can be
exploited.

I have never observed this, though I always head for "tendrils" or
clumps of cloud forming below the nominal cloud base, as the lift is
usually much better. The movement, if present, has been invariably
upwards. What speed are the cores rotating at? I'm sure I'd notice if it
was anything like dust devil speed.

More than once I've noted vorticity on the edege of a large
cloud, shifted my circle to it, and been rewarded with much improved
lift.

Me too, but it's not been in the horizontal plane.

Spending some time on your back, you will observe that not only are
there localized vortices, but that the entire system slowly rotates.
Sometimes it's easier to see this than at others. However, patience is
required since the rotation is very slow, but nontheless discernable.

I haven't looked for rotation this slow, and while it's interesting, it
doesn't seem relevant to the choice of circling direction.

Best to start with a wisp and watch its full development. Choose one
as close to directly overhead as possible. The closer your view to
directly beneath, the more obvious the cloud rotation becomes.

I'll try this next time I'm stuck on the ground under cumulus clouds.