Because of the size of the Park and its numerous elevations, Yosemite weather tends to vary depending on where you are. As a result, the conditions in Yosemite Valley at 4,000 feet can be quite different than the conditions at Yosemite's Badger Pass Ski Area, at 7,000 feet, or at Tuolumne Meadows, which is at 8,500 feet. When exploring the Park, it's important to be prepared - and always travel safely.
Additional references:
Yosemite Conservancy Webcams - see what the Yosemite weather is like right now.