On April 6, it can be seen from the satellite cloud image that on the third day of the Qingming holiday, the weather situation of "rain in the south and sunny in the north" on the mainland is quite significant: in the southern region, a large area of thick clouds flooded most of the southern provinces and regions, only Yunnan and Hainan can enjoy the sunshine on a large scale, and other provinces continue to be shrouded in rainy weather. In the northern region, the sun is clear in many places in North China, Huanghuai and Northeast China, and the temperature continues to rise.
First, the squall line is approaching the Pearl River Delta
It is already April, and the solar radiation intensity in the northern hemisphere has begun to increase, so the temperature pattern of the sunny north and the rainy weather in the south has shown an obvious "upside down" today - when the temperature is only more than 10 degrees at 10 o'clock in many places in the south of the Yangtze River, the temperature in many places in North China and Northeast China has approached or exceeded 20 degrees, and the temperature difference between the north and the south will further increase as the afternoon sun further bakes.
On the morning of April 6, the most intense weather on the mainland was Guangdong: radar charts showed a strong squall line forming in Guangdong and rapidly approaching the Pearl River Delta, with echoes in some areas turning purple to whitish, indicating extremely intense internal convective activity.
Thunderstorms, gales and hail hit many places in Foshan, Guangzhou, and Foshan Nanhai National Station received 61.6 mm of rain per hour and local gusts of 12, and the Foshan Meteorological Bureau even suggested that there may be local tornado activity. Guangzhou has a significant rainfall, some areas have 1 hour 60 ~ 80 mm of short-term super fierce rain, automatic station monitoring data show that there are automatic stations in Liwan District, Guangzhou 1 hour 80 mm of violent rainstorm.
What is the cause of this severe convective weather? In simple terms, it is the collision of cold air and warm and moist air currents. Cold air is a low-pressure air mass that is located in the northern part of the continent and is the dominant weather system in spring. It has a cold-dry airflow on its southern edge, which brings cold temperatures and dryness to the northern regions, providing instability for severe convective weather. The subtropical high is a high-pressure air mass located in the southern part of the continent and is the dominant weather system in summer. It has a warm and moist air stream on its northern edge, which brings a lot of water vapor and heat to the southern regions, providing convective energy for severe convective weather.
When the cold air moves southward and meets the warm and humid airflow of the subtropical high, 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 hail is formed. At present, the subtropical high is located near the coast of South China, which pushes a large number of warm and humid airflows into South China, while cold air from the north further infiltrates into South China, thus triggering strong convection and heavy rainfall.
Second, the fierce rainstorm locked Guangdong
What are the characteristics of this severe convective weather? First, its duration is short, with a life history of about one hour to more than ten hours, and the shorter one is only a few minutes to a few tens of minutes. Secondly, it is highly localized, and its influence range is generally a few kilometers to tens of kilometers, and the horizontal scale of the squall line is larger, which can reach several hundred kilometers. Thirdly, its elements change strongly, such as a sudden increase in wind, enhanced precipitation, and obvious changes in temperature in a short period of time. Finally, it is very destructive, causing local floods, thunderstorms, strong winds and hail, which can cause damage to houses, crops and trees, and damage to telecommunications and transportation.
For example, from the strong convection monitoring of the Central Meteorological Observatory, this morning, dense lightning symbols appeared in Guangxi and Guangdong, especially in Guangdong, dense lightning symbols appeared in the Pearl River Delta, showing that the impact of this strong convective weather is very large, it covers precipitation, wind, hail, Thunder and lightning and other strong convective weather elements, and reached a very dense and intense degree, and the impact of this strong convective weather is mainly concentrated in the Pearl River Delta region, especially Foshan and Guangzhou, where the population is dense, the industry is developed, and the urban construction is intensive, so the impact and loss will be greater.
The Central Meteorological Observatory continued to issue a yellow warning for heavy rain at 10 o'clock on April 6: It is expected that from 14 o'clock on April 6 to 14 o'clock on the 7th, there will be heavy to heavy rain in parts of southeastern Hunan, central and southern Jiangxi, central and western Fujian, central and northwest Guangdong, among them, there will be heavy rain (100~160 mm) in central and northwest Guangdong. Some of the above areas are accompanied by short-term heavy precipitation (the maximum hourly rainfall is 30~50 mm, and can exceed 60 mm locally), and there are strong convective weather such as thunderstorms, strong winds or hail locally. Judging from this early warning, on April 6, the most intense heavy rain on the mainland will appear in Guangdong.
April is the spring of the continent, and it is also the season of cold and warm air, which is the peak period of severe convective weather. In spring, the activity of cold air is frequent, and the position of the subtropical high is also constantly changing, resulting in a large difference in temperature between the north and the south, and the pressure field is also more complex, which provides conditions for the formation of strong convective weather. The forecast of the Central Meteorological Observatory pointed out that tomorrow, the scope of heavy rainfall will be slightly reduced, but the rain will be stronger in some areas of northern Guangdong, Fujian, southern Jiangxi and other places, and there will be heavy rain locally. From the 8th, the rainfall in Jiangnan, South China and other places weakened significantly, and the weather improved. Before the heavy rain weakens, Guangdong, Fujian and other places should pay close attention to meteorological information and weather warnings, and take timely measures to deal with strong convection and heavy rain.