There are many more foces at work in the mountains than just wave. The most
common is up and downslope winds. The upslope wind starts when the ground
begins to heat up and reaches a maximium around 5pm. Downslope winds start
as the air cools and flows down hill. First thing in the morning the
termperatures have pretty much equalized and the air tends to be calm.
These diurnal effects can be dramatic. Consider Hood River OR, possibly the
wind surfing capital of the world. Every morning it is calm and every
afternoon it is blowing around 25kts. This wind is predictable at Hood
River with one major drainage going from the low, moist coast to the high,
dry interior, but when you have numerous drainages interacting with each
other and complex differential heating the velocity and direction of the
wind becomes unpredicable and often varies 180deg from one end of a 1000'
runway to the other as well as having large up and down components.

It is not just a matter of comfort, it doesn't take much wind to produce
significant up and downdrafts in very rugged terrain as well as horizontal
shear. The problem is that the direction of these small-scale winds cannot
be predicted. When taking off or landing it is easy to be forced into the
ground by a tailwind or downdraft. Another problem is that many mountain
airports are one way and you can't take off or land unless the wind is
either calm or favorable.

Once you get above ridgetop level the wind starts to flow in a predicable
manner, thus the difference flying "over the mountains" and "mountain
flying" that Newps was making.

The best rule is to fly in the morning when none of this stuff is going on.

Mike
MU-2


"Morgans" wrote in message
...

"Mike Rapoport" wrote

While it is possible for an
airplane to crash into a ridge while flying upwind because of a wave, I
don't think that I have ever heard of it happening.

I never saw anyone say anything about upwind or downwind in this thread,
did
you?

While downdrafts due to thermals are a possibility, I can't imagine anyone
flying close enough to a ridge to not be able to get away from it's
"clutches", and flying into a ridge because of them. Flying early is
important for comfort, but beyond that, I don't see the relevance. All
that
is left is wave activity, it seemed to me.

Or I could be wrong, then "nevermind."
--
Jim in NC