That's great that you're planning a trip to Switzerland; it's truly a stunning country. As for the weather in mid-May, it can be a bit unpredictable. Generally, the weather starts to warm up a bit during this time, but it's still possible to experience rain and colder temperatures, especially at higher altitudes. However, if you're willing to brave the weather, you should still have some beautiful views from the mountains and be able to experience all the activities you've planned. The best way to get an accurate prediction is to check the weather forecast closer to your trip date. Use business class flights
if possible; it is much better.