Narrative:

Extreme turbulence event climbing through FL310 began to hear other aircraft encounter moderate to severe mountain wave activity approximately 20 NM north of our position and along the front range.we were approaching the front range and requested to descend back to FL310 or FL290 to avoid the mountain wave.climbing through FL350+ we finally received the clearance to descend and maintain FL310. We began the descent and began to encounter mountain wave at approximately FL317.the mountain wave began as I had previously experienced many times in the past with an increase in airspeed and an increase in our vertical speed.from the onset of the mountain wave; until we encountered what very rapidly becoming extreme turbulence; was just a few seconds.once the extreme turbulence began the aircraft was completely uncontrollable. Airspeed increased immediately to beyond vmo with the power at idle and speed brakes extended. I assumed control of the aircraft from first officer and disengaged the autopilot in order to get the aircraft pointed nose up and try to bleed off the excess airspeed. During the extreme turbulence encounter I do not believe pitch oscillations exceeded more than 20 degrees up or down. And I'm most certain roll oscillations did not exceed more than 60 degrees; though it was close. My primary focus was to get the aircraft slowed to less than 180 knots; the vturb speed; and maintain some semblance of control over the aircraft. I was able to get the nose of the aircraft pointed up enough to get the airspeed where it should be; however; the aircraft was at no time controllable until the turbulence subsided. The extreme turbulence surely did not last more than 30 seconds; but as the first officer said; 'it might as well have been an eternity.'once the aircraft was under control we diverted and ATC [gave us priority handling].prior to the extreme turbulence encounter; the ride was mostly smooth and the sky was clear. There was a small area of cloud formation; but at the time of encounter was not near our position. At no time were there lenticular clouds noted in the area.

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Original NASA ASRS Text

Title: The Captain of a Cessna business jet reported encountering mountain wave conditions followed by extreme turbulence. The result was a temporary loss of aircraft control; followed by a precautionary landing at a diversion airport.

Narrative: Extreme turbulence event climbing through FL310 began to hear other aircraft encounter moderate to severe mountain wave activity approximately 20 NM north of our position and along the front range.We were approaching the front range and requested to descend back to FL310 or FL290 to avoid the mountain wave.Climbing through FL350+ we finally received the clearance to descend and maintain FL310. We began the descent and began to encounter mountain wave at approximately FL317.The mountain wave began as I had previously experienced many times in the past with an increase in airspeed and an increase in our vertical speed.From the onset of the mountain wave; until we encountered what very rapidly becoming extreme turbulence; was just a few seconds.Once the extreme turbulence began the aircraft was completely uncontrollable. Airspeed increased immediately to beyond Vmo with the power at idle and speed brakes extended. I assumed control of the aircraft from First Officer and disengaged the autopilot in order to get the aircraft pointed nose up and try to bleed off the excess airspeed. During the extreme turbulence encounter I do not believe pitch oscillations exceeded more than 20 degrees up or down. And I'm most certain roll oscillations did not exceed more than 60 degrees; though it was close. My primary focus was to get the aircraft slowed to less than 180 knots; the Vturb speed; and maintain some semblance of control over the aircraft. I was able to get the nose of the aircraft pointed up enough to get the airspeed where it should be; however; the aircraft was at no time controllable until the turbulence subsided. The extreme turbulence surely did not last more than 30 seconds; but as the First Officer said; 'it might as well have been an eternity.'Once the aircraft was under control we diverted and ATC [gave us priority handling].Prior to the extreme turbulence encounter; the ride was mostly smooth and the sky was clear. There was a small area of cloud formation; but at the time of encounter was not near our position. At no time were there lenticular clouds noted in the area.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.