Mountain climbing is an excellent way for people to get close to nature, understand nature, and gradually come to know themselves. It is one of the outdoor leisure activities people engage in, as well as a great form of physical exercise. In addition to possessing sports and medical knowledge related to mountaineering, climbing enthusiasts must also understand the weather-related knowledge associated with mountain climbing, grasp the natural laws connected to weather, and follow these rules when planning climbing activities in order to achieve the aforementioned goals.
Generally speaking, when making their own climbing plans, enthusiasts must understand the climatic conditions and weather patterns of the climbing area, as well as the natural laws related to those conditions. This chapter mainly discusses mountain climbing at high altitudes (above 5,000m).
Mountain Climate Knowledge
There is a lot of mountain climate knowledge, primarily including the start and end times of the rainy season, changes in high-altitude winds above 5,000m, and the daily variations in surface wind speeds at different altitudes. Understanding the start and end of the rainy season is mainly to help plan climbing activities—climbing should be scheduled during the dry season and avoid the rainy season as much as possible. Knowing how high-altitude winds above 5,000m change is extremely important for climbing in high-altitude regions. According to the experience of Chinese mountaineers, for amateur climbers, it's best to choose seasons with low wind speeds (less than force 7) when climbing in high-altitude areas, and avoid windy seasons (greater than force 7). The aforementioned climatic conditions are important meteorological references for climbers when choosing the right season. Understanding the daily variation of surface wind speed in mountainous areas is mainly to assist in planning daily climbing schedules.
Choosing the Climbing Season
China’s major high-altitude mountainous regions are concentrated on the Qinghai-Tibet Plateau and the Tianshan Mountain Range.
On the Qinghai-Tibet Plateau, due to the average altitude of 4,000–4,500m and the influence of rugged terrain, strong winds often occur above 6,000m. Therefore, when climbing mountains above 6,000m on the Qinghai-Tibet Plateau, besides considering the start and end of the rainy season, it is also necessary to take into account the seasonal variations in high-altitude wind speeds to more accurately select the climbing season.
In most parts of the Qinghai-Tibet Plateau (such as the northwest and the northern side of the Himalayas), the rainy season occurs from June to September, with the heaviest rainfall in July and August; however, in the southern edge areas of the plateau, the rainy season occurs in April and from June to October. Therefore, climbing in these areas should try to avoid their rainy seasons. Generally speaking, the seasonal variations in high-altitude wind speeds above 6,000m on the Qinghai-Tibet Plateau are mainly determined by changes in the subtropical westerly jet stream (also known as the "southern branch of the westerly jet stream"), with the location of the subtropical westerly jet stream being where the strong winds occur. Statistics show that the wind speeds at altitudes of 6,000–9,000m over the Qinghai-Tibet Plateau are highest from January to March and November to December, and it is generally not advisable to climb mountains above 6,000m during these periods. Considering both of these conditions, the best seasons for climbing mountains above 6,000m on the Qinghai-Tibet Plateau are from late April to early June and from mid-September to early October.
The peaks in the Tianshan Mountain Range are relatively lower compared to those on the Qinghai-Tibet Plateau, with altitudes typically ranging from 5,000 to 7,500m. The highest peak in the Tianshan range, Tomur Peak, is only 7,435.3m. The high-altitude wind speeds in the Tianshan region are influenced by the mid-to-high latitude westerly jet stream (also called the "northern branch of the westerly jet stream"). Because the mid-to-high latitude westerly jet stream occurs at a lower altitude, the wind speeds between 5,000 and 8,000m in the Tianshan region are very high. Therefore, when climbing peaks above 5,000m, the seasonal variations in high-altitude wind speeds must be considered. This is different from climbing on the Qinghai-Tibet Plateau. The rainy season in the Tianshan Mountains occurs from June to August, and the high-altitude (5,000–8,000m) wind speeds are lower from April to July, with the smallest wind speeds occurring in May and June. Clearly, April and May are suitable for climbing.
Choosing the Climbing Time
Statistical analysis shows that in mountainous areas, the daily variation of surface wind speeds is greater than in plain areas, and the higher the altitude, the greater the daily variation in wind speed. For example, in spring and early summer on the Qinghai-Tibet Plateau, the daily variation of surface wind speed at an altitude of 4,500m is 4.5 times that at 1,000m altitude. At 4,500m altitude, the wind speed between 2 pm and 6 pm local time is on average 5.5 meters per second greater than during the night and morning. It can be inferred that at altitudes of 6,000–8,000m, the daily variation in surface wind speed is about 6–8 times that at 1,000m altitude, meaning the afternoon wind speed is roughly 7.3–9.8 meters per second greater than during the night and morning. Based on this, the mountaineering meteorology team has advised the Chinese Mountaineering Team to “set out early and camp early” when climbing at high altitudes. Since 1975, the Chinese Mountaineering Team has adopted “set out early and camp early” as one of its climbing regulations. In the Everest region, the Chinese Mountaineering Team stipulates setting out at 2 am local time and camping at 2 pm local time. Recently, mountaineers from various countries climbing to the summit of Everest, whether via the north or south slope, have advanced their departure time from the assault camp to 00:00 local time to ensure completion of the summit before 12:00 noon local time. Climbing enthusiasts may refer to this and determine their own “early departure” and “early camp” times based on different seasons and altitudes. In principle, the higher the altitude, the earlier the departure and camping times should be. The daily variation of surface wind speeds is greater in spring and autumn, so departure and camping should be as early as possible. In summer, the daily variation is smaller, so it's acceptable to start a little later. (China Outdoor Exploration Association)