I think you'll get used to it, and will get over it. It rains, a lot, but assuming you're busting your butt inside, it'll just be a small environmental blip. And an excuse to drink coffee or tea, admire the beautiful landscape from a window...
I bet you'd not be able to stand LA traffic and the smog more than the cold! And you have a friend already (see above). Plus the building where the CS department is located is really nice and they have a cafe on the first floor 7 cafe's I believe on campus!
if you're torn for that reason alone, Virgin America has a sale on flights there right now- go for the weekend and get a feel for it. Personally, I loved it. Wish WSU has wanted me though! *tear*