Winter December-February
Spring March-May
Summer June-August
Autumn September-November
Nepal has four seasons, but has a typical monsoonal character.
The dry season is from October to May and the wet season (monsoon) is from June to September.
Climatic factors are very important for planning a visit to Nepal. October to November, the start of dry season, is in many ways the best time. Monsoon has just finished, the countryside is lush and green, rice is harvested, the air is clean and visibility is great for Himalayan views. Some very important festivals are in this period.
In December and January the climate and visibility are still good, but it can get very cold. Trekkers have to be prepared for snow encounters on high altitude treks.
From February to May, the end of dry season, is also a good time to visit. The weather gets warmer, so high altitude treks are no longer arduous, although at the end of dry season, just before monsoon starts, it might be too hot for comfort.