Tibet enjoys a continental climate, with very hot summer and extremely cold winter. But the temperature of Tibet in different seasons is not only decided by the season as the altitude of Tibet varies greatly from a minimum altitude of around 3600m to 5000m at some passes. The wind at Everest Base Camp can be very cold. At altitudes higher than Lhasa the nighttime temperatures will invariably be below zero centigrade.
Besides, there is also a great difference of temperature between day and night in Tibet. For example, in Lhasa although the temperatures are mostly moderate during the day it can be very cold at night, requiring several layers or much better, a light down jacket to walk around.
Therefore, you might have an extreme range of climates and you should be prepared for all sorts of conditions on clothing.
Even in Summer, it is advisable to take down jackets with you. With a huge range in elevations, you will experience all sorts of temperatures and quite possibly all sorts of weather. It might be sunned, snowed, hailed and sleeted on some day!
Though it doesn't rain often in Tibet and usually it doesn't rain hard, normally only light drizzle, but it is not fine all the time. It can be extremely windy and cold on top of the high passes. So travelling in good vehicles that have heaters is the best choice even in Summer.
In Winter of Tibet, although it is mostly fine and sunny the day time temperatures rarely make it above zero centigrade. In Lhasa, a short shirt might be enough for you in the middle of the day, but in the morning and evening are extremely cold.
Tibet dose not have obvious Spring and Autumn in fact if just taking the temperature into consideration.
Generally speaking, from May to October, the temperature of Tibet is relatively high. This is might be biggest reason that most tourists travel to Tibet during this period. But no matter when you make a trip to Tibet, warm clothes are helpful and necessary if you plan to visit places out of Lhasa.
Planning a tour to Tibet
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