You can go for Trekking in Nepal throughout the year, depending on the trekking trail you choose. Nepal experiences four seasons: Autumn, Spring, Summer/Monsoon and Winter and accordingly the Nepal trekking season is fixed for the trekkers. Generally, Spring and Autumn are considered as the best seasons for trekking in Nepal.
Autumn season (Mid-September to early December) is considered as the best trekking season in Nepal. It is marked by clear skies, amazing weather, colorful festivals (Dashain and Tihar) and suitable climatic condition for numerous outdoor activities for trekkers and adventurers in the trekking destinations all over this country. Nepal is at its best with lush vegetations, magnificent views of the snow-capped mountains such as the Everest, Dhaulagiri, Annapurna massifs, Manaslu, Kanchanjungha, and trek across high and challenging passes, remote terrains, and villages with cultural, natural and biotic diversity unfolds magic in front of the trekkers.
Spring season (March to May) is the second best season to the autumn for trekking in Nepal. Less crowded than the autumn, spring provides the trekkers with blooming flowers of different varieties; colorful rhododendron and magnolia in the forests of hillside makes the trekking trails a paradise difficult to ignore. At lower elevations, the temperature is warmer while in higher altitude trekkers can have excellent views of mountains and experience a moderate temperature. While March and April are bit arid, May offers company of alpine flowers for trekkers.
Winter season (December to February) is most preferred for trekking at the lower elevations as some of the high-altitude passes (such as Thorung La Pass on Annapurna Trek, Laurabina Pass on Langtang Gosaikunda Trek) may be closed due to heavy snowfall at higher altitudes. Such low elevation trekking allows the trekkers to get an insight into the lifestyle and culture of the locals. Generally, the days are clear in this season and despite colder temperature you can expect suitable and marvelous scenery and relatively quite environment along the trails. Shorter days, however, shall make the daily trekking duration shorter than other seasons.
Summer/ Monsoon Season (June/July to August/September) is less preferred by the trekkers due to heavy rain, slippery trails and lousy mountain views in the usual trekking trails. Don’t get disappointed, you can still head to the rain shadow areas of Mustang, Nar-Phu and Dolpo regions that are best trekking trails for this season. An advantage of trekking in this season is the abundance of greenery and lush vegetations, clean air, fresh fruits and vegetables, butterflies decorating the trail and hence suitable for botanists. A short trekking expedition in the Annapurna region is another alternative for trekkers in Monsoon season.