it shouldn't rain at Jay, the Jay Cloud should help you out. They can predict rain, bum you out, but the next thing you know you are skiing knee deep pow pow in the trees at Jay.
Recommendations: Take the tram up and enjoy the face chutes if there is good snow. if there is no new snow, don't bother because they get super scraped off.
Otherwise, for some of the sickest tree skiing, head over to state-side and hit the trees that you see on the left as you take the triple lift up. All of those runs on stateside will assure you a good time. I personally like the run "power line" if you like to ski bumps. Otherwise, just cut into the trees even if it isn't necessarily a market glade (stay in bounds though)!.
For parks - parks at Jay kind of suck. the 720 park is located on the state side but it's pretty shitty, the features are really big (including a MASSIVE rainbow rail that I don't think I have ever seen anyone hit). A few weeks ago they had a cool cannon rail/box.
I prefer the 360 park on the tram side because you can hit some trees/bumps and cut into the 360 park on the way down because it's right before the lift. Small jumps, medium size rail/boxes.
Jay is the shit.