Nepal has four seasons, spring, monsoon, autumn, and winter. Spring is warm to hot depending on the places you visit ( see the temperature chart below). There are occassional rains but generally the weather is fine in spring. Moonsoon brings heavy rains . Autuman has very pleasant weather with clear blue sky and clear mountains . Winter gets chilly and needs really warm clothes if you are going to the mountains. Kathmandu has an elevation of 1350m ( 4500 ft approx) and Pokhara 850 m( approx), for temperature in Kathmandu and Pokhara in different months , refer the table below.
Nepal can be visited throughout the year for sightseeing tours .For trekking tours the best time is from last week of september to first week of June. However shorter treks like Ghorepani poon hill trek or Jomsom trek can be done even in summer. Summer is an ideal season for trans himalayan treks like Upper mustang, Dolpo , Nar Phu valley or for alpine flower treks as these places lie in rain shadow zone of the Himalayas.These areas experience only minimum of rain even in summer, it is warmer and vegetations grow and alpine valley floors bloom with flowers