The climate of Nepal can be broadly divided into two seasons. The dry season runs from October to May and the wet (monsoon) season rungs from June to September. Autumn (September to November) and spring (March to May) offer warm daytime temperatures, clear skies for mountain views and perfect weather for trekking, rafting or just roaming around the Kathmandu Valley.
By early December winter is starting to creep in and most trekkers retreat from the high-altitude trekking routes. Heading for Everest Base Camp at this time of the year can be a real feat of endurance, and the Annapurna Circuit is often closed by snow on the Thorung La. Even the Kathmandu Valley can feel chilly after dark, and the morning mist can play havoc with flight schedules. Tourists start to leave Kathmandu in December like flocks of migratory birds, headed for warmers climes of India or Thailand. However, this is a great time to enjoy the national parks of the Terai without the crowds.