Spring is the season of high incidence of severe convective weather on the mainland, and many places in the south have been frequently hit by strong convective weather such as thunderstorms and hail recently, which has brought a lot of troubles and hazards to people's lives and travel. From April 18th to April 19th, there was a fierce strong convective weather phenomenon such as a squall line in the south, for example, on April 18, the squall line swept through Guangdong during the day, and many places were once as day as night, and there were thunderstorms and strong winds and other fierce weather, and in the evening, the squall line appeared again in Guizhou, Guangxi, and Hunan. Thunderstorms and strong winds occurred in Guizhou, Guangxi, Hunan and other places, and hail fell locally.
1. National-level severe convective rainstorm warning superimposed
On April 19, the Central Meteorological Observatory predicted that there will be heavy to heavy rain in parts of central and southern Jiangsu, central and southern Anhui, western Zhejiang, most of Jiangxi, western Fujian, eastern and southern Hunan, northern Guangxi, and central and northern Guangdong, and heavy rain (100~180 mm) in some areas of central Jiangxi, eastern Hunan, and northern Guangdong, with the maximum hourly rainfall of 30~50 mm in some of the above areas, and more than 70 mm locally.
There will be 8~10 thunderstorms or hail in southern Guizhou, central and southern Hunan, Jiangxi, central and northern Guangxi, northern Guangdong and other places, and some areas in southern Hunan, central Jiangxi, and central and northern Guangxi will have thunderstorms and gales above level 10, and local winds can reach more than 11. The Central Meteorological Observatory upgraded and issued a yellow warning for heavy rain this morning, and also continued to issue a yellow warning for severe convective weather.
This means that the strong convection and heavy rain in the south are still continuing, and on the morning of April 19, the intense weather has kicked off: it can be seen on the radar map that the strong convective echo has appeared again in Guangdong, and there are even strong purple echoes in some places, and many places in Guangdong have once again ushered in the attack of fierce thunderstorms and strong winds.
Second, the rain belt will move south
However, the forecast of the Central Meteorological Observatory pointed out that the rain belt in the southern part of the mainland will shift to the south from the 20th, and it can be seen on the precipitation forecast map that from April 20, a wide range of purple rain bands will be aimed at Guangxi and Guangdong, and after that, the rain belt will stabilize in South China, bringing continuous heavy rain that lasts for many days.
So why is there such a strong convective rainstorm in the south? This is mainly due to the convergence of cold air and warm and moist air currents. Cold air refers to the cold air transported from high latitudes to low latitudes, which is usually accompanied by high-pressure systems and has the characteristics of high density and strong stability. Warm and moist airflow refers to the warm and moist air transported from low latitudes to high latitudes, which is usually accompanied by low pressure systems, and has the characteristics of low density and poor stability. The subtropical high refers to the high pressure system formed in the subtropical region, which is the main controlling factor of continental summer precipitation, and its strength and position change will affect the transport and distribution of warm and humid airflow.
When the cold air moves southward and meets the warm and humid airflow, it will form a particularly strong vertical movement of air movement in some areas, that is, a strong convective weather system, so that the water vapor and energy accumulated in the air can be released in a short time, so that strong convective weather such as strong thunder, thunderstorms, strong winds and even hail is formed. Severe convective weather occurs suddenly and the energy release is intense, which is dangerous.
According to the forecast of the Central Meteorological Observatory, in the next few days, strong convective heavy rain in the southern region will continue - for example, from April 19 to 21, there will be moderate to heavy rain in Jianghuai, Jiangnan, South China and Guizhou, and some areas will have heavy rain or heavy rain, accompanied by short-term heavy precipitation, thunderstorms, strong winds or hail and other strong convective weather. There was light to moderate rain in the eastern part of Northwest China, North China, Huanghuai and other places, and in the eastern part of Xinjiang and the southern Xinjiang Basin, the central and western parts of Inner Mongolia, and the central part of Gansu, there were blowing sand or floating dust, and local sandstorms or strong sandstorms.
This is due to the strong warm and humid airflow of the subtropical high and the cold vortex from the north pushing the cold air southward. The strength of the subtropical high makes the warm and humid airflow over the southern region more active, bringing a large amount of water vapor and heat to the southern region, and providing convective energy for the strong convection. The cold air from the north continues to move southward and meets the warm and humid airflow of the subtropical high, forming a clash of cold and warm airflow, which provides instability for the strong convection. Therefore, the strong convective rainstorm in the south is difficult to stop, and the rain belt is also difficult to lift northward, so it can only stay in South China, bringing continuous heavy rain that lasts for many days, and the thunderstorms and dust weather in the north are also increasing due to cold vortex activity.
In the face of strong convective rainstorms in the southern region, we should pay attention to the weather forecast and early warning information in time, make preventive preparations, and avoid unnecessary outdoor activities, especially when strong convective weather occurs, avoid being in open areas or high places, such as fields, golf courses, rooftops, tower cranes, etc., so as not to suffer from lightning strikes or strong winds, and also avoid under trees, billboards, temporary structures, etc., so as not to be struck by lightning or injured by objects. If you encounter strong convective weather outdoors, you should seek shelter from buildings or vehicles with lightning protection facilities as soon as possible, close doors and windows, and stay away from dangerous power sources.