I am sorry for coming back to you so late! I have almost missed your comment :(
The mountains in Switzerland are stunning! I love to visit them as much as I can. And I agree with you, it is great in summer too. There are so many hiking trails and you can easily spend there a few days walking around and enjoying the nature. Rigi has great facilities so you wouldn't get lost :)
The temperature nowadays is around -4 degrees Celsius. But this is not such a high altitude. If you go to around 4000 m then you get something around -20..
Thank you for stopping by and have a lovely week!