In the second half of April, around April 27, a strong cold air swept through Xinjiang, Shaanxi, Gansu, Ningxia, Inner Mongolia and northern Hebei, around April 26, including Urumqi, there was rain to snow and then rain in northern Xinjiang, and there were heavy snowfalls to heavy snowfall in Altai Mountains and Tianshan alpine areas. With the further eastward movement of cold air, from the night of April 27, there was a rare weather in central Inner Mongolia with moderate to heavy rain turning to heavy snow, and there was also snowfall and snow cover in the mountainous areas of northern Hebei.
1. Large-scale spring snow hit many Asian countries
In fact, it's not just the northern part of the continent that has seen intense and rare spring snowfall, but elsewhere in Asia, some rare spring snow has also arrived ferociously – in late April, Afghanistan saw a rare spring snowfall, which Mohammed Salim, a local fruit farmer, said had devastating effects on fruit trees that destroyed the flowers of fruit trees. People have been toiling hard, but now everything is gone. Gula Young, 53, said snowfall is rare in the spring. He lived to be in his 50s, and this was the first time he encountered it.
Spring snow refers to the snowfall that occurs in the spring, usually due to cold air moving southward or a low-pressure system moving. Spring snow has both advantages and disadvantages for agriculture, on the one hand, it can increase soil moisture and improve drought, and on the other hand, it can also cause frost damage and affect crop growth. For a large country like Afghanistan, spring snow is a disaster, because the fruit trees bloom in the spring, and when it snows, the flowers wither, resulting in reduced or no fruit yields.
According to statistics, the area of fruit trees planted in Afghanistan is about 800,000 hectares, mainly apples, apricots, peaches, cherries, etc. Fruit trees are the main source of income for Afghan farmers and an important export product for Afghanistan. Afghanistan's fruit industry, which has been ravaged by years of war and instability, has been hit by spring snow that has left farmers in despair.
Second, it is a precursor to heavy rain in the south!
Supercomputer analysis pointed out that the cause of the spring snow was the result of the recent excessive amplitude of the westerly wind belt, which caused a low vortex to move southward to the vicinity of Afghanistan, bringing relatively strong cold air and water vapor, thus giving rise to rare spring snow.
As this vortex gradually moves eastward, a southern branch trough is developing south of the Tibetan Plateau and spreading eastward, so that the water vapor transport in the southern part of the mainland is greatly enhanced, which can be said to be a precursor to heavy rainfall in the south.
The westerly wind belt refers to the westerly air flow that prevails at high altitude in the middle and high latitudes, which is an important part of the global atmospheric circulation and has an important impact on the weather and climate of the continent. The westerly wind belt is not a straight line, but a wavy belt that changes with the seasons and climate change. When the amplitude of the westerly wind belt increases, the westerly belt oscillation occurs, that is, the position and intensity of the troughs and ridges on the westerly wind belt change, thus affecting the downstream weather system.
The southern branch trough refers to the low trough active in low latitudes, also known as the subtropical westerly trough, which is the product of the weakening and southward retreat of the subtropical system and the establishment and maintenance of the westerly wind belt system, and it is closely related to the eastward movement of the westerly wind belt trough and the southern branch system formed by the large topography of the Qinghai-Tibet Plateau. The southern branch trough generally refers to the shortwave trough on the 500 hPa south branch westerly airflow, and its position and intensity will also change with the oscillation of the westerly wind belt. There is a convergence of upward motion and precipitation in front of the southern branch trough, and a divergent downdraft behind the trough, and the weather is clear. It is often the key to winter and spring precipitation on the mainland, especially in the south.
Due to the eastward movement of the southern branch trough, the water vapor transport in the southern region was enhanced, and at the same time, it was stimulated by the cold air from the south, resulting in strong convective instability, which led to a wide range of heavy rainfall and strong convective weather. The forecast of the Central Meteorological Observatory pointed out that during the day from May 3 to 5, there will be a large-scale heavy rainfall and strong convective weather process in the central and eastern regions, with moderate to heavy rain in the eastern part of southwest China, Jianghan, Jianghuai, Jiangnan and southern China, of which there are heavy rains in parts of Jiangnan and southern China, and localized heavy rains in central and southern Hunan, central and southern Jiangxi, central and northern Guangxi, and central and western Guangdong.
For example, it can be seen from the precipitation forecast that by May 3, the area of heavy to heavy rain in the southern part of the mainland will rapidly expand to Hubei, Hunan, Jiangxi, Guangxi, Guangdong, Guizhou and other places, and Hunan and Guangdong will reach the level of heavy rainfall locally, and it will be further expanded on May 4.
The medium-term weather forecast also pointed out that in the next 10 days (May 2 to 11), the cumulative precipitation in Jiangnan, South China and Guizhou will be 50~100 mm, of which 150~250 mm will be in parts of southern Jiangnan and central and northern South China, and there will be as many as 6 provinces with more than 100 mm, and more than 250 mm in Guangxi and Guangdong provinces.