Nepal’s climate varies with its topography. It ranges from tropical to arctic depending upon the altitude. In the north summers are cool and winters severe, while in south summers are tropical and winters are mild. An average temperature drop of 6°C occurs for every 1,000 m gain in altitude. In the Terai, summer temperatures exceed 37° C and higher in some areas, winter temperatures range from 7°C to 23°C in the Terai. In mountainous regions, hills and valleys summers are temperate while winter temperatures can plummet under sub zero. The valley of Kathmandu has a pleasant climate with average summer and winter temperatures of 19°C – 35°C and 2°C – 12°C respectively. Nepal's topographical extremities govern the climate condition of Nepal. Tropical, Temperate and tundra types of climate are respectively encountered in its Tarai belt, midland hills and the alpine region. Therefore people say migrating birds do not have to leave Nepal. Nepal's weather is generally predictable and pleasant.
The best period to visit the country for plant lovers is during spring when the flowers are in full bloom. Spring is colorful season which is punctuated by the odd shower of life-giving rain but the heat gradually builds until the monsoon relief arrives. During summer the Monsoon; moisture-laden wind, gathers in the Bay of Bengal and sweep up across India to spend its force on the Himalayan mountain chain. Autumn is renowned for clear skies and pleasant temperature. By winter the high hills take dry brown shades and the mountains are occasionally dusted with fresh snow.