The best season to visit Nepal is Autumn, from early October until early December and Spring, from the beginning of March until the end of April. During Autumn, the weather is generally clear with mild to warm days and cold nights. In the Spring, the mornings are usually clear but afternoon cloud build-up brings occasional showers. The days are warm and the displays of wildflowers, such as rhododendrons, are spectacular at this time of year.
It is also possible to trek during Winter, from December until the end of February. Daytime temperatures will be cooler, however, and the nights will often be very cold. The days are generally clear but occasional winter storms can bring snow as low as 2500m.
Summer in Nepal , from June to September, is the monsoon season. Trekking at this time of year is generally difficult and uncomfortable as the weather is hot and it rains almost every day. The trails become muddy and are often leech-infested and the mountains are usually obscured by cloud.
There are, however, possibilities for summer trekking in the trans-Himalayan regions of Mustang, Dolpo and Tibet . These regions lie in a rain-shadow and therefore receive significantly less precipitation than the more southerly areas.
Nepal has four climatic seasons.
Spring (between March – May) : The temperature is mildly warm in low lands while moderate in higher altitudes with plenty of opportunities to have tryst with the mountain views. It is also the time for flowers to blossom and the national flower of Nepal – rhododendron sweeps the ascending altitudes with its magnanimous color and beauty.
Summer (between June – August) : This is also the monsoon season in Nepal. The weather is hot and wet at times. It rains almost everyday with occasional thunderstorms in the evening. The rain spreads the pleasantness around with lush green vegetation.
Autumn (between September – November) : This is the best tourist season in Nepal with the summer gone by and the winter to set in. The weather is highly pleasant so are the mountain views. This is the peak season for trekking as mountain views are guaranteed so better book your flight in advance. This is also the season of festivities as Nepal celebrates the biggest Hindu festivals Dashain followed by Tihar.
Winter (between December – February) : The weather is cool and the sky is clear with occasional snowfalls at higher elevations. This season is good for trekking in lower elevations. The morning and night is cold and the days are warm when sunny.