Refer to figure.
Mountain waves are turbulent, undulating air waves that can develop above and downwind of mountain ranges. These waves can cause vertical air movements exceeding 2 000 feet per minute. The most intense turbulence is found in the rotor zone, located just beneath the wave crests. This zone is often marked by roll clouds if there is enough moisture, with the strongest rotor typically found beneath the first wave crest. Severe turbulence occurs where the wave breaks, and these areas must be avoided at all costs. Mountain waves can reach up to the tropopause.

Visual warning signs often accompany severe standing waves, particularly the distinctive lenticular (lens-shaped) clouds that form downwind of mountains. Lenticular clouds with ragged edges may indicate breaking waves and severe turbulence.

Cap clouds are another warning sign of standing wave activity. These clouds form on the windward side of the mountain, hugging the sides and top of the ridge.

1 - Roll clouds
2 - Lenticular clouds
3 - Cap clouds