How do you avoid severe turb, if flying the jetstream?
As the jetstream is like a river hundreds of miles wide and a thousand or so feet deep, generally - if you are in the jet and it is a tailwind then your ground speed will be high.
If the jet flows off in the direction of the North winding away, then you will lose the jet and your ground speed will decrease.
If your track is straight but the jet meanders off to the south, (assuming a typical Northern Hemisphere Jet flowing Eastwards) then you may cross the area of most sever turb as you leave the boundary of the jet - when your track takes you off the edge of the jet on the Polar side of the jet then you may feel turbulence depending on your level.
So - you may elect to fly at a lower level than the jet, yet enough to grab the opportunity of increased tailwind and yet far enough away from the `core` of the jet on the Polar side of the jet. How thick is the jet of today?
It may be thin, it may be narrow, in the latter case, avoidence of the `core` would be difficult.
Are there clouds in the daytime which distinguish the direction and therefore the route of the jet, yes. streaks across higher level cloud indicate a jet, look at the rest of the sky and you can fathom out from where the streaks come and therefore the direction of the jet.
But what at night? You have the forecast and upper air chart with jets and all the upper winds.
If there is a shift in the jet though and you are to cross the core due to your flight route then bumpy you will get.
Is there anyway to avoid?
Surely AWR is NOT the answer as although indicating turb, this due to droplets of water (masses thereof) and therefore at Jetstream Level there will be no AWR indication especially as we are at the tropopause, where water droplets and wx don`t exist - except perhaps for the tops of some very large CBs.
If we get a hint of swaying about or the odd crack of the nut on the ceiling then we could shift to the tropical side, a bit but - what if the jet goes south or even worse, shifts to parallel our track right where the core is - descend or intermediate level twixt traffic levels whils offsetting by 25 and talking to ATC and the boys on 121.5 and 123.4
So compliance with RVSM, for example, would be a cure but is there any prevention?