Jun 18, 2017 - 6:03 PM
in reply to Arno
<<"I can't stress enough that it's all averages when it comes to the weather. Early May can be warm too, but not as warm as July and August.">>
Certainly true and there are plenty of "microclimate" regions in Switzerland to in crease the standard deviation. (That is, the degree of variability within the average.)
However, i think I'd add:
<<"I can't stress enough that it's all ALTITUDE when it comes to the weather. Early May can be warm too, but not as warm as July and August.">>
So, early June at 2300 meters may look like late Winter, while Spring will have arrived long before, in May or June, at lower elevations.
The corollary is that in parts of May and early June, many alpine regions will have taken a break. Skiing has deteriorated, but hiking is still not possible at higher altitudes. So, many, but not all, hotels and restaurants near the Jungfrau are closed. Mountain transport tends to start up at approximately May25th.