Suzhou issued a red warning for thunderstorms and strong winds. What precautions should be taken in the face of extreme weather?

What system caused this extreme convection process? In fact, the strong convective map is the East China radar puzzle this afternoon, and the red echo from Yancheng in central Jiangsu to Jiaxing in Suzhou is the main body of this squall line. A squall line is such a weather system consisting of hundreds of kilometers of thunderstorm cell. There is an obvious angle between the moving direction and the squall line, which often brings strong thunderstorms, strong winds and hail. Today's squall line is even a little different from the general squall line-this squall line is very long and extremely strong, and the area it passes through can even have gusts of more than 12, and there are some super-single storms embedded in it, and tornado warnings have been issued everywhere it passes.

For this squall line, there is actually another name called Derecho. There is no official Chinese translation, which refers to a strong squall line system with a width of tens of kilometers and a length of hundreds of kilometers, and a destructive gust of 25m/s appeared in most areas. In fact, this kind of Derek incident will only happen twice a year in our country. It was also the Derek incident that affected Zhengzhou yesterday. Two Derecho incidents happened in two days, which is obviously unusual.

There is positive vorticity advection in front of this deep trough, which makes the air pressure in front of the trough decrease continuously and the updraft become more active. If you look at the shear line at low altitude. You will find that the groove line of this groove is in front of the 700 HPA shear line and the 850 HPA shear line. In other words, it presents a forward-leaning structure, which is a forward-leaning groove. This structure can make the dry and cold airflow guided behind the mid-high altitude trough superimposed on the warm and humid airflow in the southwest at low altitude. On the contrary, it promotes the instability of stratification and is conducive to the trigger of strong convection.

From the meso-scale environmental field, the Yangtze River Delta in East China was affected by the low-altitude southwest warm and humid air flow, and the 850hpa isohumidity line of 12g/kg was pushed to the middle of Jiangsu, and the 700hpa isohumidity reached 9g/kg near Shanghai, which was beneficial to the formation of moist convection and short-term heavy rainfall. 850hpa is in the warm center of >: =24 degrees in the middle zone, and the temperature ridge of 20 degrees extends all the way to northern Jiangsu. The Yangtze River Delta is located at the apex of the warm center temperature ridge. These conditions reflect the high energy and high humidity in the lower atmosphere and provide abundant energy for the development of strong convection.

It can be seen from the radiosonde that the convective effective potential energy of the most unstable layer in Shanghai is 2200J/kg. If the ground observation data in the afternoon (T=36.4, Td=26) are used to correct the mixed layer, it can be seen that the effective potential energy of convection can exceed 5000J/kg, reflecting extremely strong unstable energy. It should be noted that if the sounding sky rises from the ground layer in the morning, the convection suppression index reaches-150J/kg, which shows that such a large amount of unstable energy cannot be released in advance because of the low-altitude inversion layer in the morning, because it can be used because of the strong rise provided by the approach of linear convection system after the ground is fully heated in the afternoon. Judging from the equivalent potential temperature, Shanghai's 850hpa.

The biggest feature of this process is the strong wind. For this thunderstorm gale process, the gale comes from two points-the moving speed of the system and the downward momentum of the middle layer caused by precipitation drag. For the former, the moving speed of Derek, which caused this severe thunderstorm, can reach 60km/h, and the high moving speed of the system itself warns of strong winds (generally speaking, when the moving speed reaches 12m/s, it means that there is a strong wind of magnitude 8, so we should pay attention to the storm of 19m/s). For the latter, strong precipitation resistance is the key factor causing extreme winds.

Observing the convection conditions, except for the high convective available potential energy, the precipitable water in the whole layer reaches 65mm, which is beneficial to the occurrence of short-term heavy precipitation. Besides, 0-3km? The wind shear reaches 8m/s, and the wind shear at 0-6km is 10m/s, all of which are weak-moderate conditions, which seems to be unfavorable to the organized development of convective storms. However, this condition has been improved with the further eastward movement of the forward tilting trough and the appearance of the strong linear system itself. In this way, the convection model is more inclined to the occurrence of multi-cell storms or super-cell storms. This highly organized storm monomer has a larger influence range and time and stronger intensity. This also further increases the intensity of precipitation, wind and lightning activities.

There was a strong wind in this process. Because Huzhou radar only has one public data, its observation distance is too far (100km), so it can only be used for reference. However, on the radial velocity map of Huzhou radar, it can be observed that the speed of the strong storm unit affecting Suzhou is vague, that is to say, there is a strong wind of more than 30m/s on the radar scanning level, and this destructive wind only appears when it reaches the ground. Is there a tornado in Suzhou? Actually, it is not. It is difficult for tornadoes to land in urban areas. In this process, there is no signal such as a middle cyclone in Suzhou to indicate tornado vortex. In fact, the tornadoes we see in the network diagram are just some broken rain clouds, but they are really reminiscent of the extremely destructive wind.

Of course, it should be noted that southern Jiangsu and Shanghai, including Suzhou, are frequent visitors to tornadoes. On May 14 last year, an EF3 tornado occurred in shengze town, Wujiang District, Suzhou, causing many casualties. At present, tornado warning is being vigorously promoted in China. If the words "there may be a tornado" appear in the warning information of thunderstorm gale/lightning gale warning/gale warning, we need to pay more attention. Even if there is no tornado, this strong convection process is often weak.

There is positive vorticity advection in front of this deep trough, which makes the air pressure in front of the trough decrease continuously and the updraft become more active. If you observe the low-altitude shear line, you will find that the groove line of this groove is in front of the 700 HPA shear line and the 850 HPA shear line. In other words, it presents a forward-leaning structure, which is a forward-leaning groove. This structure can make the dry and cold airflow guided behind the trough in the middle and high altitude superimposed on the warm and humid airflow in the southwest at low altitude, thus enhancing the instability of stratification and further facilitating the triggering of strong convection.