Definition
An atmospheric wave disturbance formed when stable air flows across a mountain ridge at sufficient speed, producing a series of standing waves on the downwind side. These waves can extend for many miles downwind and reach altitudes well above the ridge, often producing strong updrafts and downdrafts, severe turbulence, and rotor circulations near the surface.
Plain English
When wind blows over a mountain range, the air keeps bouncing up and down on the far side, like ripples flowing downstream from a rock in a river. These invisible waves in the air can be smooth in places and very rough in others, with powerful rising and sinking air.
Context Anchor
Pilots encounter Mountain Wave in weather briefings, mountain flying, route planning near high terrain, and reports of turbulence or strong altitude changes downwind of mountains.
Derivation
‘Wave’ describes the shape of the airflow — it rises and falls in a regular pattern, just like waves on water. The mountain is what sets the wave in motion.
Why Pilots Care
Mountain waves can produce severe turbulence, strong downdrafts, and rotor clouds that create serious hazards, especially for smaller aircraft or those operating near the terrain.
Analogy
Think of water flowing over a rock in a stream. Downstream of the rock you see a series of standing ripples that stay in place even though the water keeps moving through them. Mountain waves work the same way, but in air.
Grounding Statement
If strong wind is blowing across a mountain range, the air on the far side may keep rising and sinking for many miles after it passes the terrain.
Intuition Check
Do not think of Mountain Wave as a visible wave on the mountain itself. The important part is the invisible rising and sinking air, often on the downwind side of the mountains.
Example Sentence 1
The pilot reviewed the SIGMET for mountain wave activity before deciding to delay the flight across the Rockies.
Example Sentence 2
The weather briefing warned of possible mountain wave activity east of the Rockies with winds at 30 knots.