A lot of JH has a Southeast exposure, so it can get pretty sun affected by early March and the temperatures at the base can often climb into the 50's. That being said, if you are an advanced skier, a lot of the northern exposures off of Sublette and Thunder lifts (which includes many of the famous double blacks, like Tower 3 chute, Paintbrush, Mushroom, Haps Gap, Thunder Bowl, the Alta Chutes, etc.) often will retain winter snow while the Hobacks and other slopes may close or become very difficult to ski. après Vous often has wonderful corn.
I've been there a fair amount in March. It is better earlier, but you can still have a great visit!
Mike