Geoff wrote :

Looking at a map makes it reasonably clear. He was downwind from and
not
much higher than a mountain range.

Which is exactly where you'd expect to find a rotor from the wave
spilling over the mountain. Flying into a rotor is more than just your
average downdraft. If it's strong, you can expect serious pitch and
bank excursions. Simply put, the plane can easily be out of control.
Combine that with IMC and loss of control would probably not be far
behind.

John Galban=====N4BQ (PA28-180)


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JGalban
Posted at www.flight.org