In the wintertime season of December - March, though it is quite cold but you'll see less tourists and during some time, the cost for accommodation and car rental will likely be lower also. And winter season now offers an increased chance to view the grand Mt. Everest clearly.
July and August would be the rainy seasons in Tibet, mainly night rain only which generally won't affect your sightseeing from the day time and often will bring some difficulty to trekking tours. This two months could see about 50 % of your annual rain in Tibet.
April, October and November often bring some dazzling clear weather and also you could feel completely comfortable within the lower altitude places.
For several popular tours, you may have to note these weather restrictions:
The Everest Region: although the Lhasa-Everest-Lhasa tour can be obtained all through the year, the Lhasa-Everest-Kathmandu overland tour could possibly be impossible in certain snow period in Jan or Feb, specially the Old Tingri - Nyalam - Zhangmu part.
Mt. Kailash and Lake Manasarovar and also the Northern Tibet (including Namtso Lake): usually not passable in the wintertime seasons from December to March.
Eastern Tibet: try to avoid travelling the Sichuan-Tibet highway from the rainy seasons of July and August.
In addition to the above climate issues you shall consider when planning for a tour to Tibet, you have to get ready for the strong sun radiation and big temperature distinction between night and day for traveling there also.URL du site internet: