There are two major factors to weigh as you decide when to go to Nepal: crowds and weather. As a general rule, the better the weather, the more people come to Nepal to go trekking. During the high tourist season in October and November, flights and hotels are fully booked and hotels and trails in the hills can be horrendously busy.
During autumn the nights are cold in the mountains, but the bright sun makes for pleasant day temperatures - in the high 20s° C, falling to 5° C at night, between 1000 metres and 3500 metres. At higher altitudes temperatures range from about 20° C down to -10° C. Mornings are usually clear with clouds building up during the afternoon, disappearing at night to reveal spectacular starry skies. During winter it is about 10 degrees colder.
Early December usually has a lull, but this is also a good trekking season. The Christmas period is cold, but this is the holiday season in Japan and Australia and these nationalities dominate flights and hotels. High passes, especially Thorung La on the Around Annapurna trek and Laurabina Pass on the Gosainkund trek are usually closed from late November to March. February is still cold, though less so as the spring trekking season of March and April approaches. The Middle Hills, especially around Pokhara, are full of dust and haze in April and May, but the high country is usually clear. Trekking tapers off in the heat of May except at high elevations.
The monsoon is a good time to visit Kathmandu, but there are few trekkers among those who come. A monsoon trek is possible if you are willing to put up with the rain, leeches, slippery trails and lousy mountain views. Flights operate throughout the monsoon to Lukla, Jumla and Jomsom, so it is possible to fly in and trek above the leech line.
Many of the new treks to recently opened restricted areas are good summer treks. Mustang and Simikot are partially in the Himalayan rain shadow, so trekking conditions are good throughout the monsoon season. Most of the restricted area treks are impossible during the winter season.
This season offers excellent weather and tantalizing mountain views. Temperature is moderate, making it a good time for any trekking. The sky is generally clear with outstanding views. Occasionally short storms may dump considerable snow at high altitudes. This season is considered as the best trekking season for the trekking in Nepal. September, October and November are fall in this trekking season in Nepal.
The winter season in Nepal is usually snow fall in the higher elevations with risk winds and colder temperatures. Hence is ideal for trekking in the lower elevation. If you are looking for suitable and incredible scenery, this is a great time to Trek in lower elevations. But it is depend upon the weather conditions. Generally, the days are clear in winter season in Nepal. December, January and February months are fall in this trekking season in Nepal.
Spring season in Nepal is also considered as the best season to do the trekking and mountain climbing. In this season offers different varieties of wild flora blossoming of the giant rhododendrons above 3000m and hunting paradise during this season, which makes higher altitude trekking more comfortable and interesting. It is mildly warm at lower elevations and quite moderate temperature at higher elevation over 4000m, which provides spectacular and excellent mountains View. March, April and May months are fall in this trekking season in Nepal.
Summer season in Nepal is monsoon with heavy rainfall which makes trekking conditions unfavorable. This season is ideal time for Trekking and tour to Tibet and Tibet. However, in some Trekking regions of Nepal connecting to Tibet and desert parts of Nepal i.e. Mustang, Nar-Phu valley and Dolpo regions are best season to do trekking which is summer trekking a great alternative. The Annapurna region in north-central Nepal also receives significantly less rain than other parts of the country during the summer months and low-altitude, short treks in this region are recommended. June, July and August months are fall in this trekking season in Nepal.
During the monsoon from June to August, trekking is not very popular due to the heavy and frequent rain showers. However, the vegetation becomes very green and lush, which makes for beautiful sceneries. In Upper Mustang, Humla and Dolpa, summer is an excellent time for trekking! These areas lie in the rain shadow of the main Himalayan range and are therefore not affected by the monsoon. Getting there might be a challenge though due to unpredictable weather conditions in the Lowlands, which generally affect flight schedules.
Nepal has four distinct seasons. Spring, from March to May, is warm and dusty with rain showers. Summer, from June to August, is the monsoon season when the hills turn lush and green. Autumn, from September to November, is cool with clear skies, and is the most popular trekking season. In winter, from December to February, it is cold at night and can be foggy in the early morning, but afternoons are usually clear and pleasant, though there is occasional snow in the mountains.
Because Nepal is quite far south (at the same latitude as Miami and Cairo) the weather is warmer and winter is much milder at lower elevations, including Kathmandu at 1400 metres. It rarely snows below 2000 metres.
The monsoon in the Bay of Bengal governs the weather pattern. The monsoon creates a rainy season from the middle of June to the middle of September. It is hot during the monsoon and it rains almost every day, but it is a considerate rain, limiting itself mostly to the night. During this season, trekking in most of Nepal is difficult and uncomfortable. Clouds usually hide the mountains and the trails are muddy and infested with leeches.
It usually does not rain for more than one or two days during the entire autumn season from mid-October to mid-December. During winter and spring there may be a week or so of rainy evenings and occasional thunderstorms blanket the hills with snow. The Himalaya makes its own localised weather, which varies significantly over a distance of a few km. Despite the sanguine assurances of Radio Nepal that the weather will be "...mainly fair throughout the kingdom", always expect clouds in the afternoon and be prepared for occasional rain.
Most of the precipitation in the Himalaya occurs during the summer monsoon. There is less snow on the mountains and on many of the high trails during winter. Everest itself is black rock during the trekking season, becoming snow-covered only during summer. There are always exceptions to this weather pattern, so be prepared for extremes. Winter snowstorms in December and January may make an early spring pass crossing difficult and can present an avalanche danger, especially on the approach to the Annapurna Sanctuary.
In Kathmandu, spring and autumn days are comfortable and the evenings are cool, usually requiring a light jacket or pullover. Winter in Kathmandu brings cold foggy mornings and clear evenings, but pleasant day temperatures with brilliant sunshine most days after the morning fog has lifted. It never snows in Kathmandu, though there is frost on cold nights in January and February. The hottest month is May, just before the rains start.
Temperatures in Kathmandu are as follows: Maximum Minimum
Temperatures in the Everest Region average 20 to 30° F (10 to 15° C) colder than the above figures up to about 14,000 feet, the highest point reached on a short Everest trek. Near Pokhara, temperatures are 5 to 10° F (3 to 5° C) warmer than Kathmandu. Remember that it will often feel quite cold because you will be outdoors all day