After a short break during the day on April 28, strong convective weather such as strong winds, heavy rains, and hail on the night of April 28 could not wait to make a comeback, and the momentum was as fierce as before, first in Guizhou and Sichuan, with large hail in Guiyang and violent storms in Sichuan. Around noon on April 29, strong thunderstorm clouds swept across Changsha, Hunan, and the local sky changed its face almost instantly, and then a storm comparable to a typhoon swept across the city, and hail appeared in some areas.
First, there is a dragon fruit-type echo in the south
However, heavy rainfall and strong convective weather in Changsha and other places are only part of the large-scale intense weather in the south, and a strong squall line is sweeping across the central and southern parts of Hunan and northeastern Guangxi from late night on April 29. The Guilin Meteorological Bureau once warned that there might be a tornado, and the maximum gust in Hunan reached 11.
Monitoring data show that from yesterday to this morning, Chongqing, Guizhou, Hubei, Hunan, Guangxi, Guangdong, Jiangxi, Fujian and Zhejiang have experienced short-term heavy rainfall, thunderstorms and strong winds and other strong convective weather -- Guitian Village, a subordinate of Longyan, Fujian, has a level 13 thunderstorm gale (37.4 m/s); Guangdong Renhua 28.7 m/s, Fujian Liancheng 28.6 m/s, 11 thunderstorm gales; Hunan Nanyue 25.1 m/s, Jiangxi Dongxiang 26.5 m/s, Wan'an 28.2 m/s, Nanfeng 24.7 m/s, Xinfeng 26.7 m/s, Huichang 27.3 m/s, Guangdong Ruyuan 25.8 m/s, Fujian Nanping 25.1 m/s, 10 thunderstorms and gales.
On the morning of April 30, the largest squall line this year was sweeping across Fujian and Guangdong, and the fiery radar echoes on the radar map were connected.
2. Large-scale dangerous weather outbreaks!
Therefore, the Central Meteorological Observatory will continue to issue an orange warning for strong convective weather at 10 o'clock on April 30, and it is expected that in the next 24 hours, there will be thunderstorms and gales or hail above level 8 in parts of eastern and southern Jiangxi, northeast Zhejiang, Fujian, southern Guangxi, Guangdong and other places, of which some areas in central and southern Fujian and central and eastern Guangdong will have thunderstorms and gales above level 10, with maximum winds of up to 12 and possible tornadoes; Some areas in southern Guangxi, central and eastern parts of Guangxi, Guangdong and other places will have short-term heavy precipitation weather with hourly rainfall greater than 20 mm, of which the maximum hourly rainfall in southern Jiangxi, southern Fujian, central and eastern Guangdong and other places will be greater than 50 mm, and the maximum can reach more than 80 mm.
What is a squall line? A squall line is a narrow severe convective weather zone with a small range, a short life history, and abrupt changes in air pressure and wind. When it comes, there will be sudden changes in wind direction, sudden increase in wind strength, sudden rise in air pressure, and sudden drop in temperature. Because of its great power, some people call it an "aircraft carrier" in severe convective weather. Two conditions are generally required for the formation of a squall line: first, there is a strong horizontal temperature gradient in the lower layers, that is, the junction of cold and warm air, and second, there is strong wind shear in the upper atmosphere, that is, where the wind speed or direction varies greatly with the altitude. When these two conditions are met at the same time, it is possible to form a squall line.
The forecast of the Central Meteorological Observatory indicates that there is even a risk of tornadoes in some areas. Tornado refers to a weather phenomenon in which a high-speed rotating column of air is produced in a convective cloud system due to the action of strong updrafts and horizontal wind shear, extending from the base of the cloud to the ground, and has extremely destructive power. The formation of a tornado requires three conditions: first, there is a warm and moist airflow in the lower layer, which provides sufficient water vapor and unstable energy, second, there is strong wind shear in the upper atmosphere, which provides horizontal vorticity and vertical wind speed difference, and third, there is cold air in the middle layer, which enhances the vertical temperature gradient of the atmosphere. When these three conditions are met at the same time, it is possible to form a tornado.
At present, there is a possibility of tornadoes due to large-scale severe convective weather outbreaks in the southern region. For example, not long ago on April 27, at around 15 o'clock on April 27, a strong tornado appeared in Zhongluotan Town, Baiyun District, Guangzhou City, and the tornado affected a distance of about 1 km, bringing casualties and serious infrastructure damage.
On the one hand, the subtropical high is strong and westward, causing the southern region to be affected by warm and humid airflow, with higher temperature, higher humidity, and increased atmospheric instability, which provides favorable thermal conditions for the occurrence of severe convective weather. On the other hand, cold air from the north continues to move southward, forming an obvious intersection zone of cold and warm air flow with the warm and humid airflow from the south, which enhances the horizontal temperature gradient of the atmosphere and provides favorable dynamic conditions for the formation of the squall line.
In conclusion, with the formation of the intense squall line, severe convective weather with wide range, high intensity, long duration and deep impact is sweeping the southern part of the continent. Moreover, according to the forecast of the Central Meteorological Observatory, after entering May, there will still be heavy rainfall and strong convective weather in the southern region, which may be accompanied by thunderstorms, strong winds, hail, tornadoes and other disastrous weather.