There were SIGMENTS out for sever turbulence just east of Japan and north.

Typical for the Jet stream coming off of Japan this time of year 200+ mph.

I was on AA 176 NRT DFW few years back. We hit sever 45 minutes from Tokyo for 10-15 seconds but the damage was done. Food everywhere, drinks, dishes, people's laptops hit the overhead bins. It was a mess but nobody was hurt. Captain came on and said they could see Standing Lenticular Clouds and that's what we hit!