The best time to visit Tibet is from May to October; this period is not very cold, usually above 10 degrees Celsius and is the busiest time of the year in Tibet.
Rainy season in Tibet spans from July till August, however, except for the southeast, the region doesn’t get a lot of rainfall.
If you are looking to for a camping trip, May to September are the best months. For those planning to travel to Mt. Everest, April, May, September, and October is when you are more likely to see unobstructed views of the mountains.
For travelers more interested in Tibetan festivals, August is the best month; it is the time for many festivals like the Shoton Festival, Nagqu Horse Racing Festival, and GandenThangka festival. Late September to October bring out autumnal/fall colors in Tibet.