Planning for the weather is an important factor for making your trip to Yosemite National Park a success, especially when you're splurging. The hottest months are usually July and August, with an average temperature of 15°C, while the coldest months are February and December, with an average of -3°C. The rainiest months in Yosemite National Park are December, January, March and February, with each month seeing an average of 193 mm of rainfall.