Autumn season (Sept-Nov) being the best season for trekking, offers excellent weather and tantalizing mountain views, and also best season for peak climbing.
Summer months (June-September) of the year which coincides with monsoon begins in mid-June and drains in mid-September making travel wet and warm. The mountain views may not be at their best as rain clouds and haze over hang the mountains occasionally obscuring the enchanting views. These times are blessed for the keen botanist as the higher valleys and meadows blossom with flowers and lush vegetation.
Spring season (March-May) is the expedition season and the best time for climbing the high peaks. It is mildly warm at lower elevations but occasional haze mars beautiful view of mountains. At higher elevations over 4,000 meters the mountain views are excellent and the temperature is quite moderate even at night.
Winter season (December-February) is noted for cold weather with occasional snowfall at higher elevations. Again, excellent views are common. These months are popular and ideal for trekking for those who are well equipped or who remain at lower elevations below 3,000 meters.
Most of the hotel owners will come to the lower altitude cities like Kathmandu and Pokhara
Although Travel in Nepal can be organized throughout the year, October through May is considered to be the best months for trekking.