Spring (March, April, May) and autumn (Sept, Oct, Nov) are Nepal’s best time of year. The weather is good with powerful sunshine and water. The sky is clear, so you can really enjoy the beautiful Nepalese landscape with the Himalayan view.
Although there is no problem with trekking during the monsoon (June, July, Aug), the issue may be less visibility and rain. Yet monsoon is a blessing for a keen botanist as the higher valleys, mountains, and meadows blossom with flowers and abundant vegetation. You can also walk in winter (Dec, Jan, and Feb) particularly in the hilly regions, but when you reach higher elevations, snowfall is much colder. If you don’t need to experience crowds, choosing more solitary trekking destinations maybe your choice during the monsoon or winter. Remember that global warming has changed the daily climate worldwide, and Nepal is no exception. Please always be open to erratic conditions. Read more Climate and weather in Nepal