Pitchlink asked, "As an asside I wonder if anyone can explain to me why the CAT B WAT graphs indicate an increase in weight with decrease in windspeed at altitude."
This is the way you are allowed to load the helo beyond the tail rotor's control range - expressed by the way you lose crosswind capability when you load up higher. At the higher weight you use more main torque - more torque than the tail rotor can handle. That is why the allowable crosswind is reduced to nil at the higher WAT curve weight - above the lower weight limit, you will lose yaw control if you try to land hover or take off.
Nice, huh? Sort of a great way to make an LTE event, and get to blame the pilot while publishing capability that is bought by challenging the pilot beyond reason, IMHO.