There are four main seasons in Nepal. The best seasons to visit Nepal are spring and autumn. Trekkers can trek from from mid February to early June. In April/March, the hillsides are covered with blooming rhododendrons in Annapurna, Manaslu, Dhaulagiri and Langtang trekking regions. The sky is clear in the morning and generally windy with occasional thunder showers in the afternoons.
The rainy or summer season is not suitable for trekking because of the rain. However, Mustang and Dolpo region towards north-west of Dhaulagiri does not recieve rain as the cloud flowing from the south is blocked by the range. So, trekking can be organized in this area even in summer. In the rest of the country, the next trekking season starts in mid-September and goes up till late November. During this period, the visibility is good and it does not rain usually. You can get excellent views of landscapes and mountain ranges in this season.