Tibet’s dry and rainy seasons are very distinct. Usually it rains at night in Lhasa
area. Under the alternate control of west wind in winter and southwest monsoon in summer, Tibet’s dry and rainy seasons are very obvious.
Tibet Dry Season
Each year from October to April of the next year is the dry season. The westerly jet is over the Tibetan plateau’s sky and the ground is controlled by the cold high-pressure. The weather during this period is drought with strong wind, less rain and snow with low temperature. The precipitation only accounted for 10-20% of the annual precipitation, and Lhasa’s precipitation from October to April is only 3% of its annual precipitation, so called this period the dry (dry) season or wind season.
Tibet Rainy Season
From May to September, Tibet enters into its rainy season gradually.
The ground layer is controlled by thermal depression, and southwest monsoon climb to the plateau. Affected by the southwest monsoon, rainfall in parts of Tibet is very concentrated, generally accounting for about 90% of annual precipitation. Such as Lhasa, precipitation from May to September precipitation accounts for 97% of total annual precipitation, so called this period the rainy or wet season. During the rainy season, there are more night rain, more thunderstorms and hail. Southern Tibet is mostly rain at night which can account for over 80% of the precipitation during the rainy season. In northern Tibet, it is more frequent thunderstorms and hail. Such as Nagqu
, Sog County and other places, there are over 85 thunderstorm days. North Tibet is the region with most thunderstorm days compare with the regions of the same latitude in the northern hemisphere. Tibetan plateau’s number of days with hail is also the highest in the country. Nagqu’s average annual hail days are as many as thirty five days. In 1954, its hail days is sixty-four days, which is rare in the world.