Switzerland

I went up to Jungfraujoch and it was cloudy.     It was nice (summer but still cold), but I think I missed out on the views a lot.    Might be nice in the snow, but you wouldn't get the views of the mountains...

Here's a webcam I was told about (after we walked around in the clouds ) so you can see what the weather is like (keep in mind it changes rapidly during the day).

http://www.swisspanorama.com/

If you can book the tour (or just the train) with the option of staying in Interlaken if the weather isn't nice on Jungfraujoch, that might be a better place to spend a rainy/cloudy day.... I have better memories of Interlaken (sun!) than Jungfraujoch (clouds....).    If you do go and the weather isn't nice, the trip up (and back down) is pretty cool.... cable cars (I think) and you have to switch a few times. 

We stayed twice in a little family hotel halfway up a mountain (Rigi) just outside Kussnacht on Lake Lucerne.  Woke up to cowbells every morning.  We like staying somewhere like that rather than big tourist meccas like Lucerne -- but close enough for a day trip.  You can go up Mount Pilatus from there.  We had SwissRail passes which were good on just about every mode of transport.  Love the lake steamers.