I spent around a month in Langtang in April 1996 - arrived last few days March, left start of May. Apparently it had been an unusually snowy winter, there was lots of snow around and the Gangja La was impassable, even on skis. Tsergo Ri, the 4900+m peak near Kyangin Gompa, was knee-deep snow all the way to the summit. The valley floor itself was not too bad, I could go all the way up to, and just past, Langshisha Karka, but in the side valleys it was snow around 4000m. I spent a few days camped up in the valley between Gangchempo and Ponggen Dopku. Generally I thought the weather was pretty crap - it would be sunny on many mornings, but with afternoon storms that brought light snow down everywhere, most of which burnt off. Not great climbing weather. Also, above about Langtang village, the wind picks up in the early afternoon and really howls, making walking down-valley pretty unpleasant.