I usually snowboard in spring but this year we're going up to tahoe next monday and will be there til sunday. I plan on wearing my shell but I don't know what to wear under. I was thinking my under armor(thermal), sweater, and maybe a t-shirt. Would this keep me warm enough on a 25-35 degree day with a chance of snow?
Your underarmour+t-shirt+light hoodie or sweater+shell would be a good combo for that temperature range. Usually I board around 25-30 temp and I wear 1 long sleeve shirt, 1 tshirt, hoodie, and my shell. Works perfect for me. Never too hot or cold. I think if you wear any more than that you'll be too hot.
I was in that exact temp today and was perfectly happy in my Target bought Champion base layer top and bottom with my shells. Even had my helmet vents open most of the time. If I had worn anymore I would have been over heating. Everybody is different. Just remember to never wear cotton on the hill.