Nepal possesses various kinds of climate throughout the year. It has cool winters, pleasant moist springs, hot wet summers and fantastic autumns. Regarding the trekking in Nepal, almost it is possible throughout the year. It highly depends where you want to visit. The most popular season for the trek is the spring and the autumn where the mountain views ae clear, no mud and the perfect clear sky. In monsoon summer, you can trek in the Himalayan rain shadow area like Dolpo and Upper Mustang. Winter is extremely cold in the Himalayas and the high passes treks are not recommended due to heavy snowing. However, you can trek almost a year in most of the normal route.
The Monsoon Summer (June to Mid August)
Monsoon season is regarded as one of the low season in Nepal but still lot more long stay travelers. Besides trekking, you can make your program for other adventurous sports or Tours. You can still trek in the rain shadows area like Mustang and Upper Dolpo as they this region has little rainfall. The jungles are lush, vibrant and tropical. It is time to cultivate the field so most of the people will be engaged in the fields if you make any travel in Village. It is best idea to explore the villages and do some tours in this season.
The autumn (Mid August to Mid November)
The autumn is the perfect season for the trekkers. It comes after the monsoon with all clouds gone and clear skies with many opportunities to see the mountains. This is classic trekking time, famed for clear skies and fantastic fine weather. At this time, the surroundings changes from a lush, verdant green into the harvest colors. It I the busiest time for the trekkers and you will find the trails little crowded. This is the season to head off the beaten track to Kanchenjunga, Manaslu, Makalu and the regular classic trek to Annapurna Base Camp, Everest base× Camp etc. Above the tree line, when you hike more than 3500m, you will feel little chilly in the morning and nights. If you do not want to miss the panorama of the mountains of Nepal, you better come in this season as it offers the magnificence view of the world highest peaks and the lifetime experience of trekking.
The winter (Mid November to Mid February)
The wintertime is pleasant cold weather. Although trekking in this is possible and lot more do, but the high passes are not recommended. The skies are clear, the trails are dry, the temperature at night goes minus and the warm cups of tea freshen up mind and body in the trekking. If you have good gears to tackle yourself with the snow and the cold, you probably can try trekking up to 4000m level and it can be done. Famous treks like Annapurna Sanctuary, Jomsom Muktinath, Langtang Trek, Helambu are reliably accessible and pleasant.
The spring (March to May)
This season is regarded as one of the best season for the trekking. In this season, the skies are clear and you can encounter various kinds of flowers all along the hillsides. Most of the routes are covered with the rhododendron forest and you will not miss any of the mountain views. It is considered as second best season for the trek but this time is perfect for the alpine flowers and mountains.