[Ref AC 00-6B Chapter 17, AC 00-57]
Mountain waves are a form of mechanical turbulence which develop above and downwind (Lee side) of mountains ridge.
Risk of Mountain waves?
- Range: This mechanical turbulence may extend 600 miles (1,000 km) or more downwind from the mountain range.
- Intensity: This mechanical turbulence are classified as severe to extreme turbulence.
- Vertical coverage: The effect of this mechanical turbulence can cover up to 200,000 feet (20 times of FL200)! – far higher than modern airliners’ cruising level.
Clouds related to Mountain waves
When sufficient moisture is present in the upstream flow, mountain waves produce interesting cloud formations:
- cap clouds
– cover the ridge of the mountain
- cirrocumulus standing lenticular (CCSL)
– lee side of the mountain, middle clouds in the stationary group
- Altocumulus Standing Lenticular (ACSL)
– lee side of the mountain, high clouds in the stationary group
- rotor clouds
– lee side of the mountain, lowest cloud in the stationary group