Trekking Season & Weather in Nepal

BEST TIME FOR TREKKING
generally speaking, the best months to trek/tour is October-November (post-monsoon) and April-May (pre-monsoon). It is possible to trek/tour throughout the year.  
Below are details of weather conditions throughout the year.

AUTUMN: October-November
Autumn is normally dry, stable and very clear. Temperatures are usually moderate during this period making it a good time for any trek. It can be cold at night higher up, but not as cold as the winter months (December-January). At low elevations it may still be hot during the day. Autumn is the most popular time for trekking in Nepal.

WINTER: December-January
Winter is usually dry and it is a lot colder. Snow can fall in regions as low as 2500m, sometimes lower. It may be difficult to reach some of the higher passes (4000m+) due to snow & ice. The high-altitude treks require good gear and experience in cold-weather conditions as temperatures at 5000m can drop below -20°C and heavy snow can fall.

SPRING: February-April
Spring sees the return of warmer weather in the mountains and there is also more likelihood of rain. The warmer weather also brings more trekkers though as in autumn. This is mainly due to the poor cloud that comes out during this time. By April, good views are really only limited to the higher routes of 4000m +. However, it is in April that the most colorful rhododendrons bloom, between 2000m and 3000m.

PRE-MONSOON: May-mid June
It gets that much hotter, hazier and unsettled in May & early June. The warming Asian landmass has begun drawing up air from the south, ushering in the pre-monsoon – a season of erratic weather and increasingly frequent afternoon storms. If you are looking for solitude on your trek, this is a good time to go. It is also a good time for going high but be prepared for rain, especially in the traditionally wet areas of Annapurna and eastern Nepal.

MONSOON: mid-June to September
Few foreigners trek during this period because of the rain, mud, leeches, travel difficulties caused by landslides and general lack of mountain views. However, some treks in Nepal’s far west are sheltered from the impact of the monsoon. And even in wet areas, mornings are often clear, and wild flowers and butterflies can be seen in abundance.