Some background: I am not a pilot, but a researcher studying air-flow across mountain terrain using Computational Fluid Dynamics (CFD).
During my studies, I have been particularly interested by high-altitude ridges (2 to 3000m a.s.l., say 10000 ft) that are exposed to regional winds that are generally across the ridge. I have been seeing very interesting turbulence patterns above, and in the lee of the ridges (rotors).
Here is the question: what instructions are given to pilots needing to cross such a ridge at low heights above the terrain, in either direction relative to the wind? What does common sense dictate?
I am naturally thinking mostly of helicopter pilots doing mountain work, but any other aircraft are very welcome (fire-fighters, ULMs ...).