There is not a particular best season to trek in Nepal-meaning Nepal is open for trekking all seasons. However, there are best seasons as per trekking regions. Weather is a huge factor when deciding to plan your trip-especially a trek to Nepal.
This is the time of core winter in the Himalaya. Extreme cold temperatures can lead to heavy snowfall in the mountains. While it is usually nice and warm in the first half of the day, the second half can be snowy and increasingly colder as the nighttime befalls. Trekking in the mountains in this season is challenging, the snow making the trek more difficult than usual.
This is not the recommended season for trekking, however, those who like a challenging trek even during the extreme weather.
This is the most favorable time for trekking in the Himalaya, especially the Everest region. Because the weather is so good, you get unobstructed views of the mountains, hills and the glaciers. It starts getting relatively warmer from mid-March with only occasional snow falls in the high altitudes. Clear skies and pleasant weather make this season the busiest in the Himalaya.
This is another perfect time for trekking in the Himalaya. It is right before monsoon rainfall starts in Nepal. Trekking regions like Annapurna, Everest, Langtang, and Manaslu see quite many trekkers this season making for the friendly environment while trekking. The views are clear; there is no snow blocking the path while there might still be occasional rainfall in the higher altitudes.
This is the peak monsoon season in Nepal. The monsoon winds from the Bay of Bengal bring quite the downpour in Nepal. It is not advised to trek during this season. The roads are slippery and, flooding and landslides are quite common. Flights to Lukla and Jomsom among other high altitude airports get often canceled due to weather issues.
However, regions like Upper Mustang, Dolpo and upper regions of Annapurna do not receive all that much rainfall as they fall under the Himalayan rain shadow. Those regions can still easily trek even in the monsoon with an adequate amount of precautions.
This is another perfect time of the year for trekking in the Nepalese Himalaya. The monsoon completes its cycle with August bringing clearer skies for September. Temperatures are pleasant, raining from 20 degrees Celsius during the day to 5 degrees in the night.
This is also the festival season in Nepal. The two most celebrated festivals-Dashain and Tihar, fall in these two months, so cultural treks are popular as well. It is the best time to trek the Everest region; the views are magnificent. Same goes for other trekking regions like Annapurna, Manaslu, and Langtang.
This is the transition period from autumn to winter. While autumn/fall is pleasant in the Himalaya, winter can be harsh. Now, slowly temperatures start dropping, and snowfall begins.
November is the clearest month, with clear and sparkling views of snow-capped mountains. From December, the temperatures start to fall, and there is snow is most of the Himalayan trekking regions. High passes might be affected due to snowfall. However, trekking in overall is still possible.