The weather in Sion in September is very cold with temperatures between 2°C and 15°C, warm clothes are a must.
You can expect rain for roughly half of the month of September in Sion. We’re expecting roughly 8 to 15 days of rain, so your rubber boots and umbrella are going to see plenty of use this month if you’re keen on staying dry.
Please note that Sion can expect a few days of snow in September.
Our weather forecast can give you a great sense of what weather to expect in Sion in September 2025.
If you’re planning to visit Sion in the near future, we highly recommend that you review the 14 day weather forecast for Sion before you arrive.
Temperatures
15° / 2°
Rainy Days
11
Snowy Days
2
Dry Days
17
Rainfall
132
mm
Sun Hours
10.4
Hrs
