Planning for the weather is a good way to make your trip to Martigny relaxing and enjoyable, especially when you’re splurging. The hottest months are usually July and August with an average temp of 53°F, while the coldest months are January and February with an average of 22°F. The rainiest months in Martigny are May, July, June, and December, with each month seeing an average of 8 inches of rainfall.