December in Nepal is chilly up in the mountains with night time temperatures well below zero. Down on the plains though, temperatures are cool and pleasant. It never gets really cold at lower elevations and it never snows in Kathmandu. The cooler weather is ideal for visiting the national parks and exploring the ancient capitals of the Kathmandu valley such as Bhaktapur and Patan.
Taking a holiday in Nepal in December can work out surprisingly well.
It’s Nepalese winter, so it's colder than earlier in the year, but take the right clothing and you'll be perfectly fine. You'll be rewarded too with uncrowded hiking trails and wildlife watching spots. Hikers will find that above Namche Bazaar it’s properly cold with temperatures at night well below zero. But with plenty of thermal layers and a good sleeping bag, trekking is perfectly practicable. Up in the mountains the days tend to be dry and bright too, but they are a little shorter at this time of year. Popular trails that can get crowded in peak season like Poon Hill and treks around Namche Bazaar are wonderfully uncrowded.
December is typically a dry month too, so it's ideal for sightseeing or wildlife watching. Average temperatures in Chitwan National Park are in the high teens.