Autumn (October - December).
The weather is clear during the autumn season. The days are pretty warm, but the nights are cold. It is freezing in the higher elevation. It is the festival time in Nepal and also the mountains views are crystal clear.
Winter (January - February).
The days are cold in low lands and hilly region, but it is minus temperature in the high Himalayas. Except sometimes, the days are clear. There will be heavy snowfalls at the higher elevation and sometimes also at the lower elevation of 2500m. January and February are the coldest months. Travel and trekking are adventurous during the winter season.
Spring (March - May).
Spring is another season of fine weather. The mornings are clear and slightly cool, but it can be thundering and occasional rain. The days are warm and the views are interesting. It is the season of blooming various flowers and greeneries prevail on the forest. Most of the trekking trails are colored with rhododendrons. It is a snow free time, even in the Himalayan regions and trails. Around the end of April, the days are cloudy.
The summer/ monsoon (July - August).
The monsoon season in Nepal starts from June and remains till the mid of September. The mornings are cloudy and it rains the whole day, especially in the months of July and August. Thunderstorms are usually in these months. Except the trans-Himalayan regions of Dolpo and Mustang, all the other trails become muddy so the travel activities are quite difficult. Small streams become larger and there is possibility of frequent landslides in the hilly areas.