JP 3-50 National Search and Rescue Manual Vol I - US Navy

strength of the wind and steepness of the slope. If the wind
is fairly strong (15 to 20 knots) and the slope is steep, wind
will tend to blow off the slope and not follow it down. In
this situation there will probably be severe turbulence
several hundred yards downwind of the ridge just below the
top. Under certain atmospheric conditions, a cloud may be
observed at this point. On more gentle slopes turbulence will
follow the slope, but will be more severe near the top.
b. Orographic turbulence will be affected by other
factors. The intensity will be less climbing a smooth surface
than climbing a rough surface. It will not follow sharp
contours as readily as gentle contours.
c. Convective turbulence, caused by rising air currents
created by surface heating, is most prevalent over bare areas.
It is normally found below 2,000 feet above the terrain, but
may reach as high as 8,000 feet. When practical, flight paths
should be over vegetated areas. Morning searches will often
avoid the convective turbulence.
2. When crossing mountain peaks and ridges at low altitude under
windy or turbulent conditions, the safest crossing is
downwind, where downdrafts will be met after the terrain is
crossed. If this is not practical, altitude should be
increased before crossing. The safest ridgeline crossing may
be at an angle, so a shallow descending turn away from the
terrain can be made if unexpected weather or turbulence are
encountered.
3. When wind blows across a narrow canyon or gorge, as shown in
Figure 8-1, it will often veer down into the canyon.
Turbulence will be near the middle and the downwind side of
the canyon or gorge.
8-3