Sion, where it's located

The climate of Sion is moderately continental, with cold winters and warm summers.
The city is located in the south-west of Switzerland, in the canton of Valais, at 490 meters (1,600 feet), in a valley oriented from west to east, where rainfall is scarcer than in the rest of Switzerland.
The average temperature of the coldest month (January) is of 0.3 °C (33 °F), that of the warmest month (July) is of 20.4 °C (69 °F). Here are the average temperatures.
Sion - Average temperatures
Min (°C)-4-21491214131060-3
Max (°C)471217212427262217105
Min (°F)252834394854575550433227
Max (°F)394554637075817972635041

Precipitation amounts to 605 millimeters (23.8 inches) per year. It ranges from 35 mm (1.4 in) in the driest month (April) to 65 mm (2.6 in) in the wettest (December). On average, 44 cm (17 in) of snow fall per year. Here is the average precipitation.
Sion - Average precipitation

On average, there are around 2,090 sunshine hours per year: in Switzerland, the sun shines so often only in the Canton of Ticino. Here are the average sunshine hours per day.
Sion - Sunshine


Best Time

The best time to visit Sion is from mid-May to mid-September, since it is the warmest and sunniest of the year. However, we cannot exclude some rain, or a bit of cool weather, or even cold, especially in May and early June.