Cold is going to be your friend here. There's no reason at all why you can't use the jacket you have provided it doesn't rain really hard. Up to a point cold is going to be your ally because it will play to the strengths of the jacket you have. The downside of your jacket is if it is warmer and wet, because although your jacket should shed snow quite readily it won't hold out against rain pounding down on it for very long. Drizzle yeah, but wind driven rain no chance. The other shortcoming of your jacket is the MVP figure, but hey, if you don't find it a sweat box now the chances are you won't then, especially since you mention a lot of camp loafing rather than load hauling. If it were my money I'd be loading up on a good light dedicated rain shell to take in addition to the jacket you have. That'll have you optimized for all eventualities.
^ That. Plus I would add a fleece liner and maybe a light wool sweater/shirt.
If you take along a fleece liner (any lightweight fleece jacket will do) and a good quality rain shell like mentioned above in addition to your snowboard jacket, those 3 items will provide you a layering system that should get you through just about anything; any one or two of those combined will probably cover 90% of the situations you'll be in, and all 3 (fleece, then snowboard jacket, then rainshell) should cover the worst case scenario.
Wool provides warmth even if it is wet - wool comes in handy to wear if you have to dry out your other layers, or as a base layer if you need to be bulletproof;
Just remember that cotton is a killer in the cold and wet, so pay attention to your base layer next to your skin, and ensure it is some sort of poly or moisture-wicking fabric that is not cotton. It doesn't have to be a high-dollar poly shirt, either; get a package of 3 tshirts in the underwear section that are 100% polyester, or poly-wool blend and you're set for your base layer.
Lastly, dont pile everything on and overheat/get sweaty. Keep the spare layers in your pack in case you need them. Same thing for layering on your legs:
Long undies made of polyester or poly-wool blend, then a layer of fleece, then a waterproof/resistant layer like your snowpants. Not necessarily all at the same time. mix and match according to the conditions just like your upper half. One spare set of wool/fleece to wear while the others dry out.
Same with the socks; a layer of very thin polyester socks for wicking moisture, then some sort of wool/wool-blend sock like you probably already wear boarding. I use dress-socks like you would wear with a suit for my base layer. You can buy expensive poly or silk sock liners at the outdoor stores, but dress socks are the same thing, work just as well for a fraction of the price. Same for the poly underwear-you can usually find it cheap at a suerstore like Target, and it works just as well as the high dollar stuff for a base layer. Spend your money on a very good quality rain shell like 'taco says, and you'll never regret it.
Don't forget a warm hat.
Sheez, I got on a roll here...sorry if I rambled.
