we recently went thru a classic warm-rain-turns-into-freakin-cold weather cycle--classic scenario for freezing up subie windows. it was especially noticeable in southern ME, less so up north where they got less rain
down in the window regulator hardware, there are a couple of fuzzy-surfaced pads that guide the side glass up and down. when these get wet and then freeze, guess what? once they break free, it's OK...it's just breakin em free that's an adventure sometimes. pushing out a little (JUST a little) on the side glass helps here.
frameless glass also likes to stick to the window seals around door openings. you can minimize this with protectant or silicone spray