The weather in Yosemite National Park can change rapidly anytime during the year. Elevation plays a major role in temperature and precipitation. Most of the moisture comes in the months of January, February and March, and the winter climate is relatively mild. Wawona is normally very mild because of its 4000 ft elevation. Sierra summers are typically warm and dry. April and November are transitional months, when warm, sunny days can suddenly become stormy. Clouds can build up during the summer to produce spectacular thunderstorm activity.
It is wise to pack for any season with clothing that can be "layered", ready to peel off or add on as the weather dictates. Always include some kind of rain gear.