On April 17, the rain in Northeast China and Sichuan and Chongqing today was clear, and the temperature immediately rose sharply, and the cooling brought by the cold air in April was difficult to suppress the temperature for a long time without relying on rain. In contrast, many places in the Yangtze River Delta, Yunnan, southern Jiangnan and South China are in the cooling zone under the influence of rainy weather today, showing that the impact of lack of sunshine on the daytime temperature has been very significant, and the temperature in many cities in Northeast China this afternoon is even higher than that of cities in the Yangtze River Delta.
1. National-level severe convective warnings continue
Recently, many places in the southern part of the mainland have been hit by strong convective weather, resulting in frequent disastrous weather such as heavy rains, thunderstorms, strong winds, and hail, which have had a serious impact on people's production and life.
According to the yellow warning for severe convective weather continued to be issued by the Central Meteorological Observatory at 10 o'clock on April 17, it is expected that from 14 o'clock on April 17 to 14 o'clock on the 18th, there will be 8-10 thunderstorms and strong winds or hail in parts of southern Zhejiang, northeast Fujian, southern Guizhou, Guangxi, central and western Guangdong, northwest Hainan Island, northeast Inner Mongolia, western Heilongjiang and other places, and local winds can reach more than 11.
Judging from this forecast, compared with the previous strong convection and heavy rainfall in the Yangtze River Basin, the focus of severe convective weather on the mainland began to shift to the coast of South China on April 17. Corresponding to the strong convection warning, with today's strong convection flow battle between Guangzhou, Guangdong Zijin, where the strong convective cloud swept by, recorded a 12-level gale of 34.6 m/s at 14~15 o'clock in the afternoon, refreshing the record of this station.
Second, dangerous weather aims at the Pearl River Delta!
In fact, at 6 p.m. on April 17, the Central Meteorological Observatory also continued to issue a yellow warning for severe convective weather, indicating that large-scale dangerous weather will continue tonight and tomorrow.
It is expected that from 20 o'clock on April 17 to 20 o'clock on the 18th, there will be 8-10 thunderstorms and strong winds or hail in parts of southern Guizhou, Guangxi, Guangdong, northern Hainan Island, Ningxia, northeast Inner Mongolia, western Heilongjiang and other places, among them, some areas in southwest Guizhou, northwest and central and eastern Guangxi, central and southern Guangdong will have thunderstorms and gales above level 10, and local winds can reach more than 11. In fact, it can be seen on the forecast map that the Pearl River Delta region of Guangdong will become a focus of severe convective weather, with local winds exceeding level 11, and in some areas, strong convective winds may even be close to the power of typhoons.
Severe convective weather refers to the small and medium-scale weather systems that occur in convective cloud systems or single convective cloud masses, and the horizontal scale of such weather is generally less than 200 km, and some are only a few km. There are six main manifestations of severe convective weather, namely squall lines, tornadoes, hail, thunderstorms and gales, short-term heavy precipitation and thunderstorms. These weather have a common characteristic, that is, the duration is short, the locality is strong, the elements change strongly, and often accompanied by lightning and thunder, hail, thunderstorms, winds, tornadoes, etc., so the destructiveness is very strong, will cause local floods, mountain disasters, etc., can cause houses to collapse, crops and trees to be damaged, telecommunications and traffic damage, and even cause casualties.
The formation of severe convective weather is mainly due to the instability of the atmosphere and the abundance of water vapor. The instability of the atmosphere refers to the distribution of air pressure, temperature, humidity and other elements in the atmosphere in the vertical direction, if the air in the upper layer is colder than the air in the lower layer, then the atmosphere is stable, because the air in the upper layer is heavier and not easy to rise; if the air in the upper layer is warmer than the air in the lower layer, then the atmosphere is unstable, because the air in the upper layer is lighter and easy to rise. When the atmosphere is unstable, if a warm and moist air flow is lifted, then it will be affected by buoyancy during the ascent process, accelerating its rise, forming a strong vertical motion, that is, strong convection. The abundance of water vapor means that the atmosphere contains enough water to ensure the sustainable development of strong convection, because when water vapor condenses into clouds, it will release a large amount of latent heat, which will further enhance the instability of the atmosphere and promote the strengthening of strong convection.
3. Locally close to typhoon
The formation of this severe convective weather is mainly due to the combined effect of cold air and warm and humid airflow. Beginning on April 15, a wave of cold air moved south from Siberia and affected the northern part of the continent, bringing strong winds to cool the dust weather. This cold air then continued to push southward, forming a significant cold and warm air mass with the warm and humid airflow over the southern region, resulting in a wide range of severe convective weather in Jiangnan and South China.
It can be seen from the numerical simulation forecast map of the Central Meteorological Observatory that by the afternoon of April 18, strong convective clouds will erupt in southern China, and the purple-red simulated echo will approach the Pearl River Delta region of Guangdong in a big way, which means that after the large-scale strong convection in the south shifts to the south on April 17, a key point of strong convective weather will fall in the Pearl River Delta area of Guangdong, and there are more than 11 winds in the current forecast, and the strong convective winds in some areas may even approach the power of the typhoon.
In April, the direct point of the sun has been in the northern hemisphere and moved further northward, the atmospheric energy is becoming more and more abundant, and it is normal for the scale and power of severe convective weather to gradually increase. However, severe convective weather often occurs suddenly, and the energy release is violent, which is dangerous. We should pay close attention to weather forecasts and early warning information, keep abreast of the development and changes of severe convective weather, and take preventive measures. Also try to avoid outdoor activities when strong convective weather comes, stay away from tall buildings, billboards, power poles and other objects that are prone to collapse in strong convective weather, and do not stay in dangerous areas such as hillsides, rivers, and trees.