A window assembly for a vehicle includes a fixed frame having a pair of opposite side frame members, an upper frame member and a lower frame member. A fixed window panel is disposed at a lower portion of the side frame members and at the lower frame member. A movable window panel is movable relative to the fixed window panel and the frame between an opened position and a closed position. Each of the side frame members includes a lower channel for receiving a side perimeter edge region of the fixed window panel and an end region of the lower frame member. An elastomeric seal is overmolded along the lower channel of the side frame member and is configured to receive and seal against (i) the side perimeter edge region of the fixed window panel and (ii) the end region of the lower frame member.