In term of the best time to visit Nepal depends on what type of trip you are doing in Nepal. Nepal is broadly temperate with four main seasons. Its climate varies as per topography and altitude. Nepal is having various altitudes. The low range of Tarai region is maximum altitude of 305 miters, hilly region in between Terai and the Himalayan region is from 500 miters till 3000 miter altitude. The maximum altitude at the mountain region is up to 8848 miter Mount Everest. Most of the foreigners arrive in for trekking in Nepal, another numbers of foreigners are interesting tours in Nepal skipping any adventure.
Autumn is the main season for Trekking in the high mountain region. (September to November)
The Autumn season is the best season for trekking in Nepal. Weather is clear, dry, and neither cold nor hot. Dust and pollution washed away by the monsoon rains. The mountains are the most visible. This is considering as best season in Nepal for trekking in the high mountain region. It is better to book your trip an advance, since hotels and flights are booked from previous. Major Hindu festival Dashain and Tihar is also during this season. Besides trekking, any kind of tour in Nepal is suitable during these months.
Spring is second high season for trekking and expedition in Nepal (March to May)
Spring season is mildly warm weather and longer days. It is also the best time for trekking in high mountains and viewing wildlife. The major expedition including Mount Everest trip runs in these months. Most of the Nepal Trek Tours run in this season. Flowers blooming time makes a colorful hilly and low level of the mountain region. The different colored Rhododendron flowers bloom at mountain region makes fascinating together with clear Mountains peaks.
Winter is the low touristic season (December to February)
Weather in winter in Nepal is mostly clear and stable. Days are sunny but morning can be chilly. You still can face the mountain cold at this time. Trekking is lower altitude runs well even though some of the high mountain trekking like Everest Base Camp Trekking, Annapurna Base Camp Trekking, Gokyo valley trekking, Langtang valley Trekking without crossing any icy passes at high altitude. You could see a very gorgeous view of mountain peaks with its full ice. Some of the peak climbing activities in this season still go.
Monsoon season-low touristic season (June to August)
Monsoon season in Nepal is almost raining every day. The temperature is hotter. Mountains are mostly covered by fog after afternoon time. Morning time you normally will get very fresh view of peaks. Greenery hills, fresh air, movements of different butterflies make your Nepal trip more fascinating. There is some rain shadow trekking areas in Nepal which are more suitable to trek at monsoon season. Upper Mustang Trekking is one of those. Beside Any treks and tours in Nepal, monsoon season is a good season for Tibet tour. A good number of tours to Tibet run through Nepal. Most famous is Mount Kailash Tour and Nepal Highland Treks is one of the operators of this tour.