The Weather and Climate of the Himalayas

If you have not been to the Himalayas before you might make the mistake of thinking the climate is fairly uniform across the entire mountain range but nothing could be further from the truth. If you’re planning a trip its key to understand how the weather changes throughout the year in each part of the Himalayas. The Indian monsoon is the main driver of climate and the impact of the monsoon or lack of it is of key importance for predicting the weather.

A monsoon is best described as a seasonally reversing wind system. It works because during the hot part of the year the sun warms up the earth’s surface causing the atmosphere to rise and as it does it pulls in moist air from the ocean. When the sun is no longer heating the surface during the winter this mechanism reverses and a generally dry subsiding air mass dominates. The monsoon first reaches the Himalayas in far eastern India, Bhutan and Nepal in early June and remains over these regions for the longest time. For this reason, the western Himalayas in contrast to the eastern Himalayas are much drier and the monsoon starts later in the year.

When to Visit the Himalayas
Let’s jump first to how the weather impacts where you can visit in the Himalayas and when is the best time to visit.

Region Season to Visit
Kashmir June to Sept
Ladakh June to Sept
Lahaul and Spiti June to Sept
Himachal Pradesh Mar to May & Oct to Nov
Uttaranchal Mar to May & Oct to Nov
Nepal Mar to May & Oct to Nov
Tibet April to September
Sikkim Mar to May & Oct to Nov
Bhutan Mar to May & Oct to Nov
Arunachal Pradesh Mar to May & Oct to Nov

 

Himalayas Map

Himalayas Map

Kashmir : Kashmir is only lightly influenced by the monsoon but heavy snows in the mountains preclude trekking during the winter. The best time to visit is from the middle of June to Sept. The abundant snowfalls give rise to the beautiful pine forests, rivers and lakes in the region. See More: Treks in Kashmir.

Ladakh : Ladakh is almost always dry as the Himalayas block monsoon progression and create a rain shadow. High altitude and dry conditions result in extremely cold conditions in the winter. Temperatures in Leh can reach -35 °C (-31 °F) and up to 35 °C (95 °F) in the summer. The best time to visit is from June to September. Sometime the snows on the high peaks like Stok Kangri preclude trekking all the way to early July. See More: Treks in Ladakh

Himachal Pradesh : The state of Himachal Pradesh is a land of climatic extremes the region on the south slopes of the Himalayas bears the brunt of the monsoon and is wettest from July to early September. Heavy snow falls by the end of November and high elevation treks are impossible until late March when the snows melt. On the northern slope of the Himalayas in the valleys of Lahaul and Spiti the climate is more similar to Ladakh due to the rain shadow conditions that set up and block monsoon moisture. See More: Treks in Himachal Pradesh.

Uttaranchal: The state of Uttarakhand lies just to the east of Himachal Pradesh and has similar climatic patterns except that monsoon might progress a week or so earlier. The best time to visit is generally from March to May and from late September until November.
See More: Treks in Uttarakhand.

Nepal: The general trekking seasons in Nepal run from March to May and from late September until November. The Everest and Annapurna regions are of such a high altitude that winter snows are generally light and trekking is possible from December to February (See – Weather of Everest). The north side of the Himalayas which include; the Mustang and Dolpo regions, lie in somewhat of a rain shadow and monsoon moisture is more limited. If you want to trek in Nepal in July and August these are the best regions.

Tibet: Tibet lies in the rain shadow of the Himalayas and is quite dry during the summer months. Winters have limited snow but are quite cold. The best time to visit is from April until early October. See More: Treks in Tibet.

Sikkim: The Indian Monsoon is at its full strength here as moisture from the Bay of Bengal is pulled almost directly northward to the high peaks, like Kanchenjunga. The Monsoon also begins here by the end of May which is earlier then further west in the Himalayas. The best time to trek is mid-March to the end of May and in October and November before winter snowfall closes off the high elevation trails. See More: Treks in Sikkim.

Bhutan: Bhutan receives quite a bit of rainfall and the famous Snowman trek is notorious for bad weather. The best period for trekking in Bhutan is probably from early October to the middle of November. April and early May can be a secondary choice but occasional showers are common. See More: Treks in Bhutan.

Arunachal Pradesh: This far eastern portion of the Himalayas receives heavy rainfall from May to September and is best visited in either April or October.

Average dates of Monsoon Onset Across India

Average dates of Monsoon Onset Across India

A generalized cross section of the Himalayas showing Monsoon Action

A generalized cross section of the Himalayas showing Monsoon Action

Interaction between the Indian Monsoon and the Himalayas
The weather of the Himalayas is clearly influenced by the monsoon but conversely the uplift of the mountain range along with that of the Tibetan Plateau has played a huge roll on the strength of the Indian Monsoon through time. The Himalayas create a boundary between the relatively warm and moist air of India and the cold dry air mass over Tibet. The contrast between these air masses drives additional mixing. In addition, the Tibetan Plateau may act like a large heat pump due to its high surface elevation. During the summer solar heating of the surface of the surface of the plateau drives convection which pulls in moisture from India. While during the winter intense cooling of the plateau results in an outflow of cold dense air which effectively shuts off any monsoon type action. In short, the development of the boundary due to the uploft of the Himalayas over the last 10-30 million years has served to amplify monsoon across the entire Indian Subcontinent.

More Reading on the Indian Monsoon and the Himalayas
Here are some science papers you can download if you want to learn more about the Indian Monsoon and how it has interacted with the Himalayas and the Tibetan Plateau through time. Some of these get a bit complex but are good reading if you want to have more than just a general overview.

Recent Trends in the Onset and Withdrawal of Summer Monsoon over Nepal – A scientific look at the timing of the onset and withdrawal of the Monsoon in Nepal. During the last 63 year the average monsoon onset was found to be June 10 and the withdrawal September 23.

A High-Resolution Millennial Record of the South Asian Monsoon from Himalayan Ice Cores – This is a short paper looking at changes in monsoon intensity during the last 300 years as recorded by Himalayan Ice Cores.

Evolution of Asian monsoons and phased uplift of the Himalaya Tibetan plateau since Late Miocene times – This is an interesting paper looking at how the uplift of the Tibetan Plateau has influenced the strength of the Indian Monsoon.

Rising Himalayas: Advent and Intensification of the Monsoon – This paper looks at the timing of the uplift of the Himalayas and correlates with changes in the strength of the monsoon.

Monitoring the Monsoon in the Himalayas: Observations in Central Nepal, June 2001 – This paper looks at just one monsoon season in Nepal in more detail. It has an interesting discussion as to why monsoon driven convection cells continue into the night although surface heating is decreased.