To all the doubters..........
Northern Pacific, in the vicinity of the Aleutian Islands, Forecast (and Actual) rapid change in direction by about 60 degrees from pure Tailwind to Tailwind/Crosswind, in the vicinity of a very active front. Well SIGMETed, the aircraft ahead and behind us got a pounding, with a JAL guy behind us getting a real pounding requiring structural check in SFO.
The wind speed stayed pretty much the same, but with a rapid change in direction. Our own FDR recorded that the change took place over a 21 second period. We were already at Turbulence Penetration speed (M0.82), and rapid idle thrust and full speed brake deployment could not stop the upwards speed trend vector, reaching M0.882. All that data from the FDR, not subjective pilot report.
JAL was grounded for 4 days, at the time of his encounter, the pilot's voice on the radio sounded like that of a chopper pilot.
Regards,
Old Smokey