Weather in Lhasa - The Rainy Season

The rainy season in Lhasa is from July to September. The rainfall there averages 500 mm a year. Some people may worry that if they visit Lhasa in the rainy season, the schedule may be influenced and the mood would get bad. However the worry is totally unnecessary as the rainy season in Lhasa has its unique characteristics.

Weather in Lhasa – Unique Characteristics of the Rainy season

The weather in Lhasa has its own characteristics, especially in the rainy season. The rain falls mostly at night. So even if you visit Lhasa in the daytime in the rainy season without taken any rain gear with you, you would not be caught in the rain. The sunlight and the ultraviolet rays in the daytime are very strong; tourists need wear sunglasses in the daytime. But things are different at night. It often rains at the late night and at dawn.
In the rainy season in Lhasa, it does not rain from 12:00 to 3:00pm. While the night falls, the stars which are first appear in the sky are covered by the gathered dark clouds and soon the rain falls. Around 2:00 in the midnight, the rainfall reaches the highest that the lightning flashes and thunder rumbles with rains and sometimes hails. When a bit of pale ray appears in the east, the rain turns small. The clouds open and the rain stops. The sky gets very clear and the sun is shining fiercely. When the sun sets, the dark clouds gather again and the rain falls again. This happens almost everyday in the rainy season.

Weather in Lhasa –the Causes of the Rainy Season

The causes of the rain at night in the rainy season are mainly affected by the geographical and topographical conditions as well as the large-scale weather influence. In the daytime, the mountains are bathed in solar radiation. Low-pressure area is formed as the heating area of the mountains is large and the temperature rises fast. On the contrary, high-pressure area is formed in the valleys as the heating area is small and the temperature rises slowly. Airstreams rise from the valley, form valley wind and then become clouds, which are like steamed breads with convex upper apex and flat bottom.
In the daytime, as the solar radiation is strong, the droplets of the clouds absorb heats then evaporate. So the weather in the daytime is fine because the clouds get thin and sometimes disappear. While the sun sets, the temperature of the earth's surface drops sharply, the mountains get cold soon. The cold air sinks and the warm air in the valley rises, which increase the movement of the atmosphere of air and provide conditions for rain. Furthermore, the topside of the clouds get cold while the lower sides remain warm, hence the air convection are enhanced. The clouds instability increased, which contributes to the condensation of water vapors. Finally, the night’s rain occurs.