Tibet is one of the harshest places for human existence.It has highland climate, with lower temperatures and less precipitation than most of China; thin atmosphere; long hours of sunshine; and intense solar radiation.
The atmosphere is severely dry nine months of the year, and average snowfall is only 18 inches, due to the rain shadow effect whereby mountain ranges prevent moisture from the ocean from reaching the plateaus.
Solar radiation is extremely strong in Tibet. The sunlight in Lhasa is so intense that the city is called Sunlight City. The thin Tibetan air can neither radiate nor absorb heat, resulting in temperature extremes during both day and night.
The period from April to October is the best time to visit Tibet, outside of the coldest months which is generally from November through May during which time strong winds are common occurrences. June through to September is the wettest months, but the countryside will be the greenest. July and August are the best time to visit Northern Tibet where it enjoys warm temperatures, intense sunshine, beautiful scenery, and festive events.
Although southern Tibet is relatively mild during May through October, most rainfall does come during June through to September. The heavy rain blocks roads and make it difficult for travel. However, during this season, the scenery is at its best and many great festive events are held in the preferred locations of Lhasa, Shigatse, and Nyingchi.
Tibet is cool in the summer. Lhasa is probably the most humane city in Tibet, although the temperature may exceed 29oC (84oF) in the summer, and rainfall may be heaviest during the months of June through to September.
Tibet is always excruciatingly cold in the winter where temperature can plummet to minus 16 degrees Celsius (3 degrees Fahrenheit). The coldest months are from December through to February. In northern Tibet, the average temperature is subzero and winter lasts from October through May or June. In eastern Tibet, May, June and September are the height of the tourism season. In winter, roads are all blocked by rain and sometimes heavy snow. Landslides are frequent occurrences, making it difficult to travel.
Detailed information about the average temperatures and rainfall in Lhasa are as follows: