May weather in much of Switzerland is usually pleasant, much like the Middle Atlantic or lower New England states.

The mountains have their own weather, though. So if the mountains are on the itinerary (as I'm sure they are if they've picked the best spots in Switzerland) the weather will be a bit different for sure.

Cooler certainly. Possibly a little wetter, possibly occasional storms. Frequently spectacularly beautiful days. The mountains are unpredictable in the summer, and even more so in the spring and fall.

Beyond the historical weather for the lowlands, two articles may help a bit in explaining what's ahead: http://twenj.com/swmurrenfall.htm http://twenj.com/bovisit.htm#weather Ed