Mar 25, 2020 - 6:02 PM
We were in Zurich, Lucerne, and the Jungfrau region for two weeks last October. Strictly from a weather perspective, it was a light jacket - or rain jacket - the entire time. Although we did encounter several drizzly & cloudy days in the first part of our trip due to a massive Atlantic hurricane that decided to finally expire over central Europe, the rest of the time was mild and mostly sunny. During a mid-day lunch at the Kleine Scheidegg train station, where the Jungfrau trains depart, it was "take your coat off and put your sunglasses on" time.
Since you will be there one month earlier, you should find even warmer conditions in general.
No one can predict what travel conditions will be five months from now, but the weather will be good.