Narrative:

After reviewing [weather briefing program] and discussing with our flight dispatcher; we decided to file for fl 210 from ZZZ until east of ZZZ1; at which time we had agreed to climb to fl 390. [Program] showed moderate turbulence or worse for all altitudes from fl 210 to fl 430 along the route until east of ZZZ1.during climb out with TRACON we were informed that center reported there was no reason to stay at fl 210 because there was only lt chp with ocnl mdt chp; and all flights were flying 'normal' altitudes. Based on that report we requested fl 310. We queried each controller about rides and we were told same as before. At [time] we got a report from dispatch about mdt turbulence in an area along our route. After plotting it in route 2; we determined that the area was about 25 minutes ahead of us; and that we would be thru it in about 5-10 minutes.we queried center about ride reports and were given nothing different than before; lt chp; ocnl mdt. I then called the purser and inquired about the service and advised that I was turning the seat belt sign on; and to hurry up and expect continuous light turbulence with possible occasional moderate turbulence in about 20 minutes for up to 10 minutes in duration.at approximately [25 minutes later]; we encountered severe turbulence at FL310. We immediately requested lower altitude. Altitude; attitude; or airspeed was uncontrollable; and the turbulence was so intense it was impossible to even press any buttons on the MCP. I disconnected the a/P and initiated the descent to fl 210 manually as authorized by ATC. Turbulence decreased when passing fl 290 in the descent; and shortly after I was able to reconnect the a/P.there were no injuries on board; but a lot of spilled liquids and food in the aft galley. I am not sure why the flight attendants in the aft part of the a/C had not been aware of the possible turbulence.we had the proper plan to fly at fl 210 until east of ZZZ1. In retrospect; I wish we had stayed with that plan. However; since both TRACON and center insisted it was lt chp only; with occasional mdt chp we felt conditions may have improved. I don't understand why center did not have the same SIGMET we had from dispatch. Even though we asked every new controller about the rides ahead; we actually were never sure how far ahead that controller was looking; or if he/she had any information about sectors ahead. Coordinate via sat phone with dispatch when these changes to the plan come up. We did inform dispatch about our new altitude and received new flight plans from her; but a discussion on the phone instead of text messaging may have been more productive.

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Original NASA ASRS Text

Title: Flight Crew reported encountering severe turbulence during flight.

Narrative: After reviewing [weather briefing program] and discussing with our Flight Dispatcher; we decided to file for FL 210 from ZZZ until east of ZZZ1; at which time we had agreed to climb to FL 390. [Program] showed moderate turbulence or worse for all altitudes from FL 210 to FL 430 along the route until east of ZZZ1.During climb out with TRACON we were informed that Center reported there was no reason to stay at FL 210 because there was only LT CHP with OCNL MDT CHP; and all flights were flying 'normal' altitudes. Based on that report we requested FL 310. We queried each controller about rides and we were told same as before. At [time] we got a report from Dispatch about MDT Turbulence in an area along our route. After plotting it in RTE 2; we determined that the area was about 25 minutes ahead of us; and that we would be thru it in about 5-10 minutes.We queried Center about ride reports and were given nothing different than before; LT CHP; OCNL MDT. I then called the Purser and inquired about the service and advised that I was turning the seat belt sign ON; and to hurry up and expect continuous Light Turbulence with possible occasional Moderate Turbulence in about 20 minutes for up to 10 minutes in duration.At approximately [25 minutes later]; we encountered severe turbulence at FL310. We immediately requested lower altitude. Altitude; attitude; or airspeed was uncontrollable; and the turbulence was so intense it was impossible to even press any buttons on the MCP. I disconnected the A/P and initiated the descent to FL 210 manually as authorized by ATC. Turbulence decreased when passing FL 290 in the descent; and shortly after I was able to reconnect the A/P.There were no injuries on board; but a lot of spilled liquids and food in the aft galley. I am not sure why the Flight Attendants in the aft part of the A/C had not been aware of the possible turbulence.We had the proper plan to fly at FL 210 until east of ZZZ1. In retrospect; I wish we had stayed with that plan. However; since both TRACON and Center insisted it was Lt CHP only; with occasional MDT CHP we felt conditions may have improved. I don't understand why Center did not have the same SIGMET we had from Dispatch. Even though we asked every new controller about the rides ahead; we actually were never sure how far ahead that controller was looking; or if he/she had any information about sectors ahead. Coordinate via SAT phone with Dispatch when these changes to the plan come up. We did inform Dispatch about our new altitude and received new flight plans from her; but a discussion on the phone instead of text messaging may have been more productive.

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.