March through to May and September through to mid December is the best time to visit Tibet. The rainy season is June-September, though it mostly rains at night, the monsoon can make the roads impassable. The average temperature for September to December is between 5-20 degree Celsius.
During September and October the weather is at its best and the skies are clear and blue. Though at this time the days can be warm, you should be prepared for freezing cold nights. After mid December the snows come, making the high passes along the road impassable. You should note that while travelling in Tibet, the sun can be very intense and it is most important, even though the temperatures are low, that you wear sun protection and good sunglasses and hat to prevent sun burn
