I agree with Harington. Be well prepared to get any kind of weather.
In the Swiss Alps (the weather can change within 15 minutes from sunny to rainstorm, from foggy to snow. Temperatures can drop dramatically.
You need to plan with layers.
This site is run by Ivar at in Santiago de Compostela.
This site participates in the Amazon Affiliate program, designed to provide a means for Ivar to earn fees by linking to Amazon