Gedong Festival, held at most Tibetan Temples at the end of the Tibetan year.
Main day for the masked dances is the evening of the new year.
http://xianggelila.baike.com/article-176501.html
There are confusing dates available, with some saying that the festival is held at the end of the last month, rather than the end of the 11th month.
http://www.ynnhw.com/recs/392.html
Apparently the dances were held at the end of the 11th months early in 2016.