Expert analysis of the characteristics of the recent strong convective weather and early warning

The Spring is warm, everything recovers, and the strong convective weather begins to “null up”. Right after the Ching Ming, thunderstorms, hail, strong winds, heavy rain and other strong convective weather began to become apparent. What are the characteristics of strong convective weather? Where is the difficulty in forecasting it? What is the current warning of severe convective weather? How should the public deal scientifically and reasonably with possible strong convective weather? To solve these problems, April 11, the reporter interviewed the Central Meteorological Station chief forecaster Zhang Tao.

Hidden in the ice against Guiyang, how probable is your chance of being caught in the ice?

Reporter: Just after the Ching Ming, a glutinous rice dumpling of the size of a glutinous rice dump hit Guiyang. What is the reason for this hailstorm process? How often does a hail weather usually last?

Zhang Tao: In simple terms, the atmosphere is the main physical condition for the occurrence of strong convective weather. The physical conditions mainly consider four aspects. First, the convergence of water vapor, the second is the accumulation of unstable energy, and the third is the switch to activate strong convective weather. . Usually this kind of switch mechanism is more complicated. For this strong convective weather in Guiyang, it can be said that the ground cold air intrusion is the key to start. The fourth is the high-altitude strong wind power environment, which is a necessary condition for the “growth” of hail.

The duration of hail is generally relatively short, typically a few minutes to tens of minutes for a fixed location. For hailstorm thunderstorms, the process of hailfall will be longer than the fixed time. In general, the history of a thunderstorm has tens of minutes to an hour or two. The thunderstorm has a replacement process of disappearing, regenerating, and growing. Under such circumstances, the strong convective system will last for several hours or even more than a dozen hours.

Reporter: According to the "Guiyang Evening News" report, there are citizens in the Guiyang hail. Some netizens have asked: How big is the probability of being hail? What kind of hailstone is considered "big hail"? What are the provinces with the most hail and the least hail weather in our country?

Zhang Tao: It is not easy to calculate this probability, but we can look at it from a multi-year average. According to the statistical data of our observations from 1980 to 2010 , the highest probability of occurrence of hail in China is on the Tibetan Plateau, with the highest observation site being 10-20 times per year. In the eastern plains of China, one observation site per year is average. Occurrence of 0.5-1 times, taking into account the inhomogeneity of hail and observable factors under observation sites, is actually a small probability event.

According to current observations, the number of “big hailstones” that occur in China is not particularly large. In general , hailstones with a diameter of more than 2 cm are considered “big hailstones”, and hailstones with a diameter of 5-10 cm are rare.

In China, the provinces with the most hail weather are the Qinghai-Tibet and Qinghai, but large hailstones are not so much, and small hailstones are very easy to form. The probability of occurrence of hail in the plains is much lower than that in the plateau, but it is easy to form hailstones. The occurrence of hail in the arid regions is less likely. For example, in the northeastern part of Gansu Province, the condition of water vapor is poor, and the probability of occurrence of hail is very low. China's southern Xinjiang also has a low probability of hail.

Strong convective weather is a big family with short-term strong precipitation, strong winds, heavy rain, hail, tornadoes, etc.

Reporter: The strong convective weather is a big family. Apart from the hail weather, what are the weather conditions and strong convective weather?

Zhang Tao: "Strong convective weather" has two meanings as its name suggests : one is "strong" and the other is "convection." "Convection" refers to the vertical movement of the air. Like boiling water, the bottom water is heated and rolled up. The vertical movement driven by the difference in buoyancy is "convection." Such convective movements are strong and weak, and the convective movement of "strong convective weather" is relatively intense. The specific manifestations of strong convective weather are various, and a strong convective storm over it can show various forms such as wind and rain thunderstorms. Short-term strong precipitation, strong winds, heavy rain, hailstorms, and tornadoes all belong to strong convective weather.

Reporter: What are the seasons of the year when strong convective weather usually occurs? What are the characteristics of strong convective weather?

Zhang Tao: Strong convective weather needs cold and warm conditions. The probability of occurrence is highest at the turn of the spring and summer. From south to north, South China is from March to April , Jiangnan is from April to May , and North China is from May to July . Heavy storm convection is high in midsummer, and the probability of occurrence in autumn is lower than in spring, and the probability of occurrence in winter is extremely low.

The main characteristics of strong convective weather are small space-time scales and strong bursts, that is, come and go fast. Another is the strong locality, the specific location of poor predictability. Another point is that the conditional sensitivity is relatively strong, and it takes several conditions to closely cooperate with each other before strong strong convective weather occurs. If a certain condition is worse, there will be no events like the hailstorm in Guiyang. This also increases the difficulty of our forecast.

Reporter: What are the signs before the convective weather? Where are the difficulties of strong convective weather forecasting?

Zhang Tao: According to different time considerations, one or two days in advance, the sky is a clear skies, which is conducive to solar radiation to warm the ground. Closer to the hour, people usually feel hot during the hours of strong convective weather, which means that in the case of high-temperature and hot “sauna days”, strong convective weather is prone to happen. This process is actually unstable energy. And water vapor is accumulating. As the time approaches, you will find that the sky is surging, and there are some cumulus clouds. It is a cloud like cotton. When it is relatively large, it is prone to strong convective weather. In the near future, strong convective weather may have appeared in the distance. If you hear distant thunder gradually approaching and becoming dark (professionally known as “black cricket”), the direction of the wind turns sharply and the wind suddenly rises. It is a thunderstorm. You are not far, it will happen after a few minutes.

The fundamental reason for the difficulty of strong convective weather forecasting comes from the small scale of the weather system. In general, the cold waves, typhoons, and other processes have a long history of life, lasting for days or weeks or even longer, and a thunderstorm with a life history of only tens of minutes. From the standpoint of space, the cold air corresponds to the huge cold and high pressure on the ground, spanning thousands of kilometers, and the scale of a thunderstorm may be dozens of kilometers. For larger and slower systems, predictability is higher because our atmospheric simulation can simulate these weather processes. For small weather systems, simulations are more difficult and some small factors cannot be eliminated. Another reason is that strong convective weather systems are fast-changing and localized, creating forecasting challenges.

Strong convective weather is harmful, and public travel needs to be guarded against

Reporter: At present, how do we divide the warning of strong convective weather? Where can the public receive early warning information?

Zhang Tao: Strong convective weather warning is a short-term warning. At present, the central government's early warnings issued by the Central Meteorological Observatory are mainly about the possibility of strong convective weather within 24 hours, mainly hailstorms and thunderstorms. We classify the warning of severe convective weather into blue, yellow, and orange. Its level is related to the intensity of lightning and thunderstorms, and it is also related to the range of occurrence of strong convective weather.

For provinces and cities, the area of ​​concern is smaller, shorter, and more accurate, perhaps a few hours. At present, there are lightning warning, thunderstorm warning, and hail warning in the provinces. Due to different precipitation and topography in different regions, the types of warnings involved are also different.

For the public, receiving the strong convective weather warning issued by the meteorological department usually requires one or two days in advance to pay attention to whether there is a possibility of strong convective weather in the weather forecast, and if so, it is necessary to pay attention. The time limit for strong convective warnings is short. Therefore, we must pay special attention to whether there are strong convective weather warnings on the day. We generally issue early warnings through various channels such as SMS, TV, and the Internet.

Reporter: Strong convective weather is harmful, which will have adverse effects on production and life?

Zhang Tao: Strong convective weather involves wind and thunder and lightning, so the damage is also manifold. From the wind, the damage caused by the strong winds of thunderstorms is also varied. The following storms are the most dangerous disasters for aviation. In the event of a sudden storm during the take-off or landing phase, the aircraft can crash. . In case of strong thunderstorms, windstorms will be caused and buildings will be torn down causing casualties. The wind will also cause damage to agriculture, especially in the growing and harvesting stages of wheat. In case of strong winds, it will cause lodging and result in poor wheat harvest. In addition, a special form of the wind is a tornado. In the case of a strong tornado, the places passed will be razed to the ground.

In the case of rain, convective precipitation that lasts for several days can cause floods, and heavy rainfall in a short period of time can cause guilt. For example, in urban areas, everyone is surely familiar with the sea phenomenon. Infighting occurs in rural areas, which can affect cropland and cropland. In the case of thunder and lightning, the most influential one is also aviation, which will cause a large number of flight delays. In addition, it will also cause harm to people's lives and property and the number of deaths due to lightning strikes in our country is still relatively large.

Reporter: How should the public properly protect mines in daily life?

Zhang Tao: When thunderstorms happen, the most important thing is: Avoid becoming a commanding height. If you are in the wilderness, don't stay under a big tree or under a power pole. For the wilderness, big trees and utility poles are the commanding heights. In spring and summer, for most of China, most regions will have strong convective weather. Therefore, public travel should pay close attention to weather information and make travel arrangements and defenses.

This article is from China Meteorological Society.