Nepal has a four season temperate climate. However due to its location, landscape and power outages those seasons often dictate when the best time is to visit.
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.
Best times of the year to go trekking in Nepal
September to November (Autumn) is the peak trekking time of year for visiting Nepal. It's after the monsoon and the weather is clear. It's not too hot nor cold. Pro's are the visibility will be good and the climate. Negatives are there will be more tourists and the prices of guides/lodges will go up.
March to May (Spring) is another great time of year to visit Nepal for trekking. The earlier months can be cold but not as harsh as winter. They also lack the chance of passes being blocked by snow. Pro's included blooming flowers & more wildlife. Con's include haze and more heat heading into April.
Not so great times of the year to go trekking in Nepal
Trekking in the winter months (Dec-Feb): The weather is very cold and quite often some of the passes will be closed due to snow. Many lodges also close during these months. Pro's include clear visibility and few tourists. Con's include blocked passes and freezing temperatures.
Trekking in the Monsoon months (June-Aug): The weather is getting hot and outbreaks of heavy rain can make things very sticky. Mudslides become a reality along with many cancelled flights and leeches can be problematic.
Best time of the year to go sightseeing in Nepal
Sightseeing during the summer months (Jun-Aug): The monsoon season is probably Nepal's most unpopular season for visiting the country. Though the rains are manageable they often cause flooding which creates traffic build ups and delays. There's also the risk of landslides. Also keep in mind that at the start of the monsoon season it can get unbearably hot before the real heavy rains hit. Jungle trekking in Chitwan at this time of year is particularly brutal due to the humidity.October to February is best in Chitwan for wildlife spotting.
Sightseeing in Nepal during the Autumn (Sept-Nov): This again is Nepal's peak tourist season. Though accommodation is never really booked out in Nepal there is an influx of tourists. It's all go in the main cities and everything is functioning reasonably well. Prices are a little higher now though.
Sightseeing in Nepal during the Winter (Dec-Jan): It's cold at night and in the mornings but during the day sunny so temperature would rise upto 25 to 30 degrees depending upon the place where you are.
Sightseeing in Nepal during the Spring (Feb-May): This is a good time of year. Starting out cold and getting increasingly warm you can take your chances and choose which you prefer. Either way the weather is generally favorable and tourist numbers are not as high as they are in Autumn.
Temperature and Rainfall
The average temperature in Kathmandu during the four seasons:
* Spring season ranges between 16-23 Degree Celsius (61-73 Degree Fahrenheit)
* Summer season ranges between 23-25 Degree Celsius (73-77 Degree Fahrenheit)
* Autumn season ranges between 15-24 Degree Celsius (59-75 Degree Fahrenheit)
* Winter season ranges between 9-12 Degree Celsius (48-54 Degree Fahrenheit)
During the rainy monsoon season between June to August, it rains to an average between 200-375 millimeters in Kathmandu. There is occasional rainfall during the other seasons too. In an average, 1300 millimeters of rain falls in Kathmandu every year.
In a nutshell, you can travel in Nepal during any month of the year for both the trekking and city tours program.