Good outdoor onsen during winter time?

Me and two other friends will be going to Japan December/January this year. We're interested in going to an onsen, but not staying at a Ryokan overnight. There are just SO MANY options, we have NO idea which one to decide upon. Since we're going in the winter time, it would be nice to go somewhere with a nice atmosphere. Can anyone recommend a good onsen during winter?

On our trip, we'll be staying in Tokyo and Kyoto and will have a JR Pass to travel if that helps :)

Thank you!!

Hi!I recommend following onsen and onsen web site, but it is hard to go back in a day not staying ryokan.

Kusatsu(Gumma pref)
Nozawa(Nagano pref)
Takaragawa(Gumma pref)
Hohshi(Gummma pref)
Tanigaw(Gumma pref)

http://onsen.secret-japan.com/

thank you for your suggestions ^^
i almost thought i wouldn't get any :P

Can I just tag along here and ask which onsen or ryokan you would recommend in Nozawa as we plan on skiing there in late Jan ?

We stayed at Sumiyoshiya Ryokan at Nozawa two years ago and really loved it. It is walking distance to the escalators going to the lifts, had wonderful service & food, and a small but lovely bath. Nozawa also has a great website in English, http://www.vill.nozawaonsen.nagano.jp/info/english/start.htm, and it lists hotels and ryokans with their price ranges and contact info. There's a map too so you can see where the various accommodations are located.