Nepal has four main seasons which is mostly centred around summer monsoon. Majority of tourists in Nepal prioritize mountain visibility so, it is recommended for the travelers to visit Nepal in the autumn peak season which falls on the late September to late November. This is the period when the climatic condition is clear and dry and neither hot in the Terai and nor too cold in the high hills in Nepal. Another most important point is that this is the period when dust and pollutions are washed away by the monsoon rains making the mountains visible. And this is the same reason why it is the best time for trekking which Nepal is quite famous for all over the world.
Two main festivals in Nepal Dashain and Tihar also fall during this period. The main thing that can put anyone at the disadvantage during this period is that this is season in which Nepal receives most visitors. So, do expect some crowd and high price wherever you visit.
Winter season falls in Nepal during the period of December to January. The capital Kathmandu never receives snow but mornings in Kathmandu can be quite chlly. Cold can be fierce in the trekking regions and expect some lodges to be closed for the same reason. Whereas winter is the perfect time to visit the Terai region.
Spring season falls in Nepal during the period of February o mid-April. This is the second tourist season after Autumn in Nepal. The days are longer and warmer, Rhododendrons which is the national flower of Nepal bloom in the hills during the end of the Spring in Nepal. This is the perfect time to visit Terai for viewing wildlife since the long grasses are cut during this period.
During mid April to early June is period of pre-monsoon in Nepal which is quite known for the afternoon clouds, stifling heat and rain showers. This is the period of unrest and illness and if you are planning to visit Nepal during this period then do take care of your health.
On the other hand during monsoon that falls between the mid-June to last weeks of September it is the fascinating time to visit Nepal. Nepalese welcome monsoon since it brings rain which makes fields come alive with green shoots and rushing waters. This is the point when the air is clean, flowers bloom, fresh fruits and vegetables are abundant. The downside is the roads and paths of trekking routes may be blocked due to the heavy rainfall and landslides.