Strange high-altitude behavior

I've flown a few of the jets at 30,000-35,000 feet, but I keep experiencing what I can only describe as very strong wind gusts. I didn't think the jet stream was that gusty, but I'll be flying along, and it will yaw by 15-20 degrees. At the same time, the airspeed will change drastically, like I was cruising at 0.85 mach on the 747, and it suddenly jumped to .98 mach in a split second! I have real world weather turned on, updates every 15 minutes, and rate of change set for medium (pretty much the defaults). It's annoying because the overspeed warning goes off whenever it decides to speed way up. I guess the next thing to try would be to use fixed weather and turn off the updates, but has anybody else run into this?