![[GFH OLD wave anatomy.png]] Flow within the wave is smooth and laminar, with Altocumulus Standing Lenticular (ACSL) clouds marking the crest of the wave. Cirrocumulus Standing Lenticular (CCSL) clouds may also form at higher levels. These lenticular clouds (or "**lennies**") may exist as isolated single clouds, or relatively straight bands of clouds, downwind and parallel to the mountain range. **Foehn gaps**, or cloudless "alleyways" mark the trough of the wave. Moderate to extreme turbulence typically exists below the wave flow. Under the wave crests, horizontal roll vortices, or "rotors" form the areas with the most hazardous turbulence, often marked by rotor or roll clouds. Visually, these clouds have cumuliform qualities, but appear very ragged, with a rotating, churning motion. As long as the [[Conditions Associated with Wave]] remain consistent, the mountain wave system will remain stationary with respect to the ground. While the clouds described above appear to float motionless in the sky, in reality, they are continuously forming on the upwind/rising side, and dissipating on the downwind/sinking side. When conditions do change, so will the wave system; wavelength or amplitude may shift, new clouds may form, and the wave may get stronger, or weaken and fall apart. Moisture at varying levels will determine which, if any, clouds form. Wave can exist in clear air with dry conditions; locating the areas of rising, sinking, and turbulent air will be considerably more challenging. ![[wave clouds.png]] [<iframe width="560" height="315" src="https://www.youtube.com/embed/zxfDnr3FN7g?si=J7s1vd_U_NDXDP0q" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>]