Mountain Waves

Mountain Waves are oscillations to the lee side (downwind) of high ground resulting from the disturbance in the horizontal air flow caused by the high ground. Vertical currents within the oscillations can reach 2,000 ft/min. The combination of these strong vertical currents and surface friction may cause rotors to form beneath the mountain waves causing severe turbulence.

Mountain Waves are associated with severe turbulence, strong vertical currents, and icing.

For information on the formation of Mountain Waves, go to the separate dedicated article.
 

Controller actions when mountain wave activity is reported/forecast

• When notified of mountain wave activity, controllers should try to accommodate pilots’ requests for later descents over the mountain chain in question.
• Consider allowing aircraft to climb or descend quickly from regions with the most significant turbulence as far away from known mountain ridges as possible.
• A pilot report of a mountain wave is a special or non-routine aircraft observation. It needs to be disseminated to the local MET office in accordance with local procedures and to other pilots likely to be affected. The MET office, in turn, will issue a corresponding AIRMET (MOD MTW) or SIGMET (SEV MTW) message.