Basically, the Tibetan climate is not as harsh as many people imagine it
to be. The best time of year to be in Tibet is from April to the
beginning of November, after which temperatures start to plummet.
The central Tibet, including Lhasa, Gyantse, Shigatse and Tsedang,
generally has very mild weather from April to November, though July and
August can be rainy - these two months usually see around half of
Tibet's annual rainfall.
October and November often bring some dazzling clear weather and daytime
temperatures can be quite comfortable at Tibet's lower altitude.
The coldest months are from December to February. It is not impossible
to visit Tibet in winter. The low altitude valleys of Tibet (around
Lhasa, Shigatse and Tsedang) see very little snow.
Spring does not really get under way until April, though March can have
warm sunny days and is not necessarily a bad month to be in Tibet. More
specific information in different areas:
Lhasa - the border of Nepal/China: The Friendship highway is basically
in good conditions year around. But from December to February, the
thawed road could make some trouble Besides, try to avoid August -
landslide could happen in the rainy season.
Mt. Everest Region: Early May and early October are the best time to
visit Mt. Everest. Due to the clear weather, you have great chance to
see Mt. Everest's true face. From December to February, it's too cold to
go to this region. But the magnetism of Mt. Everest always attracts
people anytime of the year.
Ali (Mt.Kailash): Even without climate restrictions, this area is
already inhospitable. Big rain and snow could make the journey worse.
However, for those determined tourists, the appropriate time is May,
June, July, September and October.
Eastern Tibet: Don't touch this area in July or August, the rain could
ruin the road, and make terrible landslides. While in winter, the road
could be frozen.
Northern Tibet: With the average altitude of 4,500m, this area offers
very limited time for tourists. Summer is the prime time to enjoy the
great plain in northern Tibet.