Weather conditions can change quickly any month of the year–especially in the higher elevations. The higher the elevation, the lower the temperature. Moisture comes mostly in January, February and March. Winter in Yosemite Valley is relatively mild. Sierra summers are typically warm and dry. April and November are transition months when warm, sunny days can suddenly become stormy. Additionally, clouds can build up late in the day during the summer to produce spectacular thunderstorm activity.
Be prepared for quickly changing weather any time of the year. The best way to do this is bring clothing that can be “layered”–ready to peel off or add on as the weather dictates. Always include rain gear.
Only those experienced in all weather backpacking should venture on remote trails during the winter and transition months. During these same times, always carry chains in your trunk and know how to use them. Having extra rations of food and water, spare dry clothing and blankets are a wise decision too.