B737 flight crew reported severe turbulence during cruise.

Attributes
ACN	1711351
Time
Date	201912
Local Time Of Day	0601-1200
Place
Locale Reference	ZLC.ARTCC
State Reference	UT
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 176 Flight Crew Total 4916 Flight Crew Type 4916
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 206 Flight Crew Total 10325 Flight Crew Type 10325
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Inflight Event / Encounter Loss Of Aircraft Control Inflight Event / Encounter Weather / Turbulence

Narrative:

At cruise we were informed of moderate turbulence and light to moderate mountain wave at various altitudes about 10 minutes ahead. Severe turbulence was reported at FL410. At our altitude the turbulence was reported as light to moderate. We stayed at our altitude due to the fact that all altitudes above FL310 were reporting some turbulence and I didn't want to take the fuel hit to descend to FL310 or below. We expected nothing worse than light to moderate turbulence and some mountain wave. We had the flight attendants seated with seat belt signs on and made 2 separate announcements warning the passengers of the possible impending turbulence. We were at mach .78. We experienced moderate to severe mountain wave coupled with severe turbulence. We lost roughly 700 feet and gained a plus 400 feet during the wave. We experienced stick shaker as the autopilot attempted to recover the altitude before I clicked it off and unloaded to approximately 0 to -.5 gs. Speed got down to approximately 240 kts. Even with the unload during the climb back up; we went as high as FL385 before descending back to FL380. During this the co-pilot informed ATC of our altitude deviations and asked for a decent to FL340. After the turbulence and wave; we initially leveled off at FL380 then descended to FL340 after confirming our new clearance to FL340. This all lasted about 2 minutes after which the flight was unremarkable.

Original NASA ASRS Text

Title: B737 flight crew reported severe turbulence during cruise.

Narrative: At cruise we were informed of moderate turbulence and light to moderate mountain wave at various altitudes about 10 minutes ahead. Severe turbulence was reported at FL410. At our altitude the turbulence was reported as light to moderate. We stayed at our altitude due to the fact that all altitudes above FL310 were reporting some turbulence and I didn't want to take the fuel hit to descend to FL310 or below. We expected nothing worse than light to moderate turbulence and some mountain wave. We had the flight attendants seated with seat belt signs on and made 2 separate announcements warning the passengers of the possible impending turbulence. We were at MACH .78. We experienced moderate to severe mountain wave coupled with severe turbulence. We lost roughly 700 feet and gained a plus 400 feet during the wave. We experienced stick shaker as the autopilot attempted to recover the altitude before I clicked it off and unloaded to approximately 0 to -.5 gs. Speed got down to approximately 240 kts. Even with the unload during the climb back up; we went as high as FL385 before descending back to FL380. During this the Co-pilot informed ATC of our altitude deviations and asked for a decent to FL340. After the turbulence and wave; we initially leveled off at FL380 then descended to FL340 after confirming our new clearance to FL340. This all lasted about 2 minutes after which the flight was unremarkable.

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.