The valleys south of the Himalaya have a generally temperate climate with typical northern hemisphere seasons but, of course, altitude makes distinct variations. During the summer, it is affected by the monsoon, a hot damp wind that blows along the mountain slopes, originating in the Indian Ocean.

Much of the high country above 5,000 metres is under the realm of snow and ice although the permanent snowline varies according to aspect and gradient. In Nepal the snowline is believed to be at 5,500 metres. Winter snowfall occurs up to an elevation of 2,000 metres and is much heavier in the western part. Owing to the high relief, glaciers are not very extensive in the Nepal Himalaya and avalanches are frequent during the warm summer season. Late summer is also the season of alpine flowers when the high pastures teem with grazing animals from lower valleys. For the mountain communities, it is the time for harvesting their main crop before their winter migration to warmer climes.

The passes in the Himalaya, which often lie along or across glaciers, are the highest in the world, with an average height of about 3,050 m (10,000 ft). All passes above about 4,880 m (16,000 ft) are often snowbound and may be closed from November to May.

Basically, you can take a trip at any time of the year – it will always be warm enough or cold enough, there are benefits to every season. However you should be prepared for the worst as mountain weather can be extremely unpredictable sometimes. Sudden rainstorms or snow flurries are always possible at high altitude. The following charts give you a guideline for different regions at different altitudes.

Winter

Winter: the air is clear, views satisfactory and the trails quieter (December to February) It offers cool to mild and clear days with often very cold nights. The mountain air is crystal clear and the views are satisfactory. The best months for lowland and middle valley treks. With few trekkers visiting the region, this leaves the mountain trails significantly quieter which could be taken advantage of.

Ghorepani starting from Pokhara at the foot of Annapurna, Helambu region, lying north of Kathmandu, and the Sherpa villages of the lower Everest region are excellent. Tour extension to Chitwan National Park for three-day jungle safari is also a good option.

Spring

Spring: rhododendron galore, views ok, forests teeming with wildlife
(March to mid-June) Haze often builds up during the day. Very warm to hot in the lowlands and increasingly warmer as the season progresses and as the clouds build up to the next monsoon, afternoon rain is common. Myriads of rhododendrons, magnolia, daphne and orchids are in bloom in the hills towards the end of this period, and in the Tarai the elephant grass for thatching has been cut, making this the optimum time for viewing wildlife. In late February and March, the dramatic mountain views provide good trekking throughout the Himalaya.

Langtang and the Kali Gandaki Valley in the Annapurna Region are ideal. In April and May, with the opening of the high passes, treks to Everest Base Camp, Around Annapurna are at their best.

Summer

Summer: profusion of wildflowers, monsoon, lush countryside, festival season
(Mid-June to mid-September) The monsoon sweeps up over India every summer from the Bay of Bengal and makes the south of the Himalayan region very wet and humid. Beautiful flowers and warm days come higher up in the Himalayas.

The Nepalese monsoon provides unique trekking through the rainshadow into the flowered valleys of Dolpo, Mustang, Nar-Phoo and Jumla which lie behind the Himalayas on the Central Asian Plateau better known as Trans-Himalayan region. It is also the time to tackle the challenging high passes such as GanjaLa, MesoKanto, KangLa, etc, which otherwise remain snowbound the rest of the year. Wild flowers are at their best in Langtang. Trips to Mt Kailash in Tibet and Lhasa-Kathmandu overland journeys are also very popular.

Autumn

Autumn: great views, lush countryside, best time to visit (Mid-September to November) The trekking season starts in Nepal at the end of September, reaching its peak during October and November. Usually regarded as the most popular time of the year to visit Nepal for any activities, the autumn days are sparkling and crisp, has generally the clearest skies with good visibility, and mild to warm days/cool nights gradually turning cooler later in the season. The countryside is lush and green as the rice harvest approaches. The two important festivals of Dasain and Tihar fall during this season, adding to the cultural interest of the holiday. It is possible to do any treks, though high altitude treks are most popular.

Nepal’s climatic types

The Sub-Tropical Climate -occurs in the Terai and inner-Terai region upto an altitude of 1200m. Summers are very hot and winters are cool
The Cool Temperate Climate -occurs in the regions of altitudes between 1200m and 2100m. The climate is moderately hot and winters are cool
The Cooler Temperate Climate -occurs in the higher parts of Mahabharat Range between 2100m and 3300m. Warm in summer and cold in winter
The Alpine Climate -occurs in the regions of altitudes between 3300m and 5000m. Summers are slightly warm but the winters are very cold, with the temperature always falling below zero
The Tundra Climate -occurs above 5000m and is similar to the Tundra regions of the Northern Hemisphere

Mean temperature

Altitude and latitude are the greatest influences on temperature in the mountains. The gradient of temperature change with altitude, known as the environmental lapse rate, coupled with latitudinal influences on temperature, produces generalised climate patterns in the Himalaya that range from tropical to frigid alpine (tundra).