Planning for the weather is a good way to make your trip to Boise relaxing and enjoyable, especially when you’re splurging. The hottest months are usually July and August, with an average temperature of 22°C, while the coldest months are January and December, with an average of 0°C. The snowiest months in Boise are January, March, December and February, with each month seeing an average of 23 cm of snowfall.