Medium Transport
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 40; Flight Crew Total 7400; Flight Crew Type 40
Situational Awareness; Time Pressure; Workload
Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Flight Crew Returned To Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Regained Aircraft Control; Flight Crew Took Evasive Action
Weather
While cruising at FL350 ATC gave a vector heading to avoid an area of severe mountain wave activity. We complied with the request promptly and turned on passenger seatbelt sign on. A short time later [we] encountered moderate clear air turbulence and the autopilot disconnected. A few seconds later we encountered what I would describe as severe mountain wave and the aircraft was having difficulty maintaining altitude. Airspeed was +/-30 knots and we lost 600 feet of altitude while trying to fly out of this weather phenomena. The entire episode lasted no more than about 20 seconds. We immediately notified ATC of our altitude deviation and that we were attempting to climb back up to our assigned altitude. ATC acknowledged and offered reroute and altitude change. By that time things got a lot better and we were able to continue to our destination without any issues. There were no injuries to passengers.Moderate to severe mountain wave was reported in the vicinity but no reports of any turbulence. We may have just encountered a pocket of moderate clear air turbulence at the same time as we encountered severe mountain wave.
A corporate pilot reported severe mountain wave activity and a brief moderate clear air turbulence encounter which disconnected the autopilot along with a 600 foot altitude loss.