The best season for trekking holiday in Nepal are Autumn and Spring of the year. The months of these season day time warm enough and night fairly cold. In autumn from mid September to mid of December almost days are crystal clear and enough sun shine and also weather condition is stable which makes high passes are easy to cross. The temperature will drop considerably as you trek everyday vary to high elevation- day time sunny and warm between 10C to 20C but wind is cold always and night between -5C to -10C depends on the places.
Same as spring season weather condition gets warm enough stable and flowers are seen blooming everywhere. In spring from end of March to May is the best time to trek in Nepal. During the monsoon and winter seasons trekking is not so much favorable due to heavy rain fall and cold as well less visibility. But in Spring seasn you can trek in no rain zone, like; Upper Mustang and Upper Dolpo area. The higher elevation areas and passes are almost covered with snow during the winter. Trekker can choose the particular time as per their convenient time frame of the months of autumn and spring seasons. Most of the lower elevation areas of trek covers mid-hill region so these region day time pleasant warm enough and morning and evenings are cold. Autumn is the best season for Nepal adventure treks.