Lhasa, Shigatse, Lhatse, Tingri, Nylam areas, along the Friendship highway the road is basically in good conditions year around. But from December to February, the thawed road could make some trouble. Try to avoid August - landslide could happen in the rainy season.
In Mt.Everest Area, early May and early October are the best time to visit there. If you visit there on a clear weather day, you have great chance to see Mt. Everest's true face. From December to February, you'd better not to go to this area because it is too cold - except you are real Great Adventure People.
In Ali area (Mt.Kailash), in fact, this area is inhospitable even without climate restrictions. Heavy rain and snow could make the journey worse. However, if you are the determined tourists, the appropriate time is May, June, July, September and October.
In Eastern Tibet, it's important for you to remember that don't go to this area in July or August (the rainy season) because the rain could ruin the road seriously, and make terrible landslides. In winter, the road could be frozen.
In Northern Tibet, this area provides very limited time for tourists because of the high altitude average of 4500meters. Summer (July to August) is the prime time for tourists to enjoy the great plain in northern Tibet.
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