If you're hoping to get lost in the rain on your romantic getaway, take a look at these details about year-round temperatures in Yosemite National Park: 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.