Air carrier flight crew reported encountering unexpected severe mountain wave turbulence.

Attributes
ACN	1519529
Time
Date	201802
Local Time Of Day	0001-0600
Place
Locale Reference	DEN.Airport
State Reference	CO
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Captain Pilot Not Flying
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Deviation - Speed All Types Inflight Event / Encounter Loss Of Aircraft Control Inflight Event / Encounter Weather / Turbulence

Narrative:

30 NM west of dvv cruise FL310 speed 0.79 mach; we encountered severe turbulence and mountain wave (ride was sooth prior to the event). Aircraft rapidly accelerated to mach 0.86 despite the use of speed breaks and the aircraft's over speed pitch up protection. During this the autopilot disconnected and I recovered the aircraft with an airspeed deviation +/- 30 knots and altitude deviation +/- 3;000 feet. As I was recovering the aircraft the captain immediately advised ATC of the altitude deviation. Once recovered to normal flight; we followed up with QRH severe turbulence checklist. Captain contacted the flight attendants for any passenger or crew injuries. No injuries were reported. The seatbelt sign was on during the event. We also assessed the aircraft for damage; and determined the aircraft was not damaged. We then made a PIREP with ATC; notified dispatch and maintenance.an early alert could have helped us avoid the turbulence. We were the first aircraft to encounter the severe turbulence. The three aircraft behind us also encountered this severe turbulence. The ride was mostly smooth prior to our encounter. ATC was reporting mostly smooth rides. The only turbulence indication on the entire flight plan was a 1 (occasional light) over denver. The aircraft was equipped with wifi and our ipads were connected; but the [weather] application would not display or update information.

Original NASA ASRS Text

Title: Air carrier flight crew reported encountering unexpected severe mountain wave turbulence.

Narrative: 30 NM west of DVV cruise FL310 speed 0.79 Mach; we encountered severe turbulence and mountain wave (ride was sooth prior to the event). Aircraft rapidly accelerated to Mach 0.86 despite the use of speed breaks and the aircraft's over speed pitch up protection. During this the autopilot disconnected and I recovered the aircraft with an airspeed deviation +/- 30 knots and altitude deviation +/- 3;000 feet. As I was recovering the aircraft the Captain immediately advised ATC of the altitude deviation. Once recovered to normal flight; we followed up with QRH Severe Turbulence Checklist. Captain contacted the Flight Attendants for any passenger or crew injuries. No injuries were reported. The seatbelt sign was on during the event. We also assessed the aircraft for damage; and determined the aircraft was not damaged. We then made a PIREP with ATC; notified Dispatch and Maintenance.An early alert could have helped us avoid the turbulence. We were the first aircraft to encounter the severe turbulence. The three aircraft behind us also encountered this severe turbulence. The ride was mostly smooth prior to our encounter. ATC was reporting mostly smooth rides. The only turbulence indication on the entire flight plan was a 1 (occasional light) over Denver. The aircraft was equipped with WiFi and our iPads were connected; but the [weather] application would not display or update information.

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.