You do NOT want to get those Diamaris or any summer tires close to near freezing temperatures. I attempted getting up to Big Bear last year on my summer Bridgestones (no snow, just wet roads at about 40F), needless to say that the X skid all over the place and I had to quickly turn around.

I don't know how often you go up to the mountains, but if you do it often enough, snows are much recommended as others have pointed out. In any case, you're required to carry chains regardless (at least to show the CHP) even if you have all-wheel-drive.