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 meters and 3500 meters. 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. 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.

Nepal climate varies according to its season. Autumn and spring are the two most favorable seasons for visiting Nepal. Autumn starts from early September to early December and brings in clear weather with sunny days and warm nights. Whereas spring starts from the beginning of March to the end of May with occasional rain falls. From June to September, is the monsoon season. Trekking is generally difficult and uncomfortable as the climate of Nepal at this time of year brings about hot weather and rain falls almost every day. The trails become muddy and are often leech-infested. Moreover, the mountains are usually obscured by cloud. There are, however, possibilities for summer trekking in the trans-Himalayan regions of Mustang, Dolpo and Tibet. These regions lie in a rain-shadow and therefore receive significantly less precipitation than the more southerly areas.

CLIMATE CONSIDERATION FOR TREKKING TRIPS
The best seasons to trek in Nepal are autumn, from mid September until end November and spring, from the beginning of March until the mid May.

Autumn (mid-September to end-November).
This is the most popular time to trek. Generally during autumn, the weather is clear with mild to warm days and cold nights. However, in the higher altitude, the nights drop into freezing temperature. In this season, the mountains views are astonishingly clear.

Approach to winter and the mid winter (End-November through March).
It is also possible to trek during winter, from December until the end of February. Daytime temperatures will be cooler; however, the nights will often be very cold. The days are generally clear but occasional winter storms can bring snow as low as 2500m. Early October through late November is also the busiest period for trekking. But in mid winter (January through March), trekking is more challenging in the high altitudes with semi-regular snowfall followed by more winter storms, which break the long fine periods. The mid-December to mid-February is the coldest time.

As snow gets harder and wind condition remains stabilized in early winter, climbing some of trekking peaks is possible. Climbing Mera peak, Island peak, Chulu, and trekking in Annapurna, Everest, Langtang in early winter have been quite popular over the past few years.

Spring and early summer (mid-March through May.

In the spring, the mornings are usually clear but afternoon cloud build-up brings occasional showers. The days are mix up with warm and rain, which displays wildflowers like rhododendrons. The whole country is lush and an abundant green at this season. This period instigate the second most popular and pleasant trekking season as this is rice-planting time. Late-march into April is especially beautiful. It is also a good time for climbing as the high passes are usually snow free and the mountain views are still clear in April. Up to May, the weather becomes hazy and disturbed with the clouds.

The monsoon (June to mid-September).

From June to September, is the monsoon season. Generally the morning is cloudy and cloud wisps form on random ridges and peaks. Trekking at this time of year is generally difficult and uncomfortable as the weather is hot and it rains almost every day. The trails become muddy and are often leech-infested and the mountains are usually obscured by cloud. During April and May, there is an expectation of thunderstorm, hail shower and strong winds among the fine periods. There are, however, possibilities for summer trekking in the trans-Himalayan regions of mustang, Dolpo and Tibet. These regions lie in a rain-shadow and therefore receive significantly less precipitation than the more southerly areas.

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