The temperature in this season is mildly warm in the Terai / southern part of Nepal and moderate in higher altitudes with plenty of opportunities to have meeting with the snowcapped mountains and massive Himalayas. This time is also the time for flowers to blossom and the national flower of Nepal - rhododendron sweeps the ascending altitudes with its color and beauty so this is the second biggest tourist season in Nepal and best time for the Himalaya expedition, peak climbing, trekking and many other adventure activities.
Summer ( From June to August):
This is the monsoon season in Nepal so The temperature is hot and wet in this time and rains almost everyday with occasional thunderstorms in the evening. The rain spreads the pleasantness around with green vegetation. So this is the best time for the River rafting in Nepal as the level of water in the river is increased.
Autumn ( From September to November):
This is the best tourist season in Nepal with the fantastic weather. This is the peak season for trekking as mountain views are guaranteed so would be a better idea to book your flight in advance. This is also the season of festivities as Nepal celebrates the biggest Hindu festivals Dashain and Tihar( Deewali).
Winter (from December to February):
The weather is cool and the sky is clear with occasional snowfalls at higher elevations. This season is good for trekking in lower altitudes. The morning and night is cold and the days are warm when it's sunny.
The average temperature in Kathmandu during the four seasons:
Spring season ranges between 16-23 Degree Celsius.
Summer season ranges between 23-25 Degree Celsius.
Autumn season ranges between 15-24 Degree Celsius.
Winter season ranges between 9-12 Degree Celsius.