China Youth Daily and China Youth Network reporter Qiu Chenhui.
At 10 a.m. on February 1, the ** Meteorological Observatory issued a freezing orange warning for the first time, which is the highest level of freezing warning issued since the establishment of the freezing warning standard in 2010. The forecast released the day before said that the central and eastern parts of China will experience the largest and longest rain and snow weather since this winter, and 10 provinces are expected to have heavy snowfall or heavy snowfall.
This will be the heaviest winter rain, snow and freezing weather since 2009, with a certain degree of extremeness. * Xu Jun, chief forecaster of the Meteorological Observatory, told a reporter from China Youth Daily and China Youth Network.
National rain and snow forecast map. **Courtesy of the Meteorological Observatory.
To the north, light gray and dark gray represent the amount of snowfall, superimposed with light purple and strong purple; To the south, the dark blue rose, which represents precipitation, is overlaid with pale green and dark green; There are large shadows lurking at the "short encounter" of the two colors, which indicates that the rain and snow will change violently here......Open the national rain and snow forecast map from January 31 to February 5, and you will see a piece of intense color.
Why is there heavy rain and snow in "warm winter"? What is the cause of this widespread rain, snow and freezing weather? What will be the impact of rain and snow on the Spring Festival? Focusing on these issues, the reporter interviewed a number of meteorological experts.
Zhao Junhu, chief duty officer of the National Climate Center, said that historically, it is rare to have large-scale and long-lasting freezing rain and snow weather in China.
The most impressive one was at the beginning of 2008, when the southern region of China suffered a historically rare freezing rain and snow low temperature disaster, which was rare in history. Zhao Junhu said that the most recent one was from January to February 2022, and there were many obvious rain and snow weather processes in southern China, but the scope was small, the intensity was weak, and the impact was not as large as in 2008.
According to the latest monitoring by the National Climate Center, the peak of the moderate-intensity El Niño event that began in May 2023 occurred in December and is now in a recession period, which is expected to continue until the early spring of 2024. According to statistics, El Niño events have the most significant impact on the weather and climate systems of the tropics and the southern hemisphere in the early stage. In the winter of the peak development period, it will affect the winter climate of the northern hemisphere.
Why is there still this heavy rain and snow in the "warm winter"? Zhao Junhu explained that in the winter of El Niño, the temperature in most parts of China is close to normal to high (there will be warm winters in some years), but the cold air is active in stages, and the temperature in China fluctuates greatly. On the other hand, in the winter of El Niño, the intensity of the subtropical high in the northwest Pacific is stronger, and the water vapor conditions in the central and eastern parts of China are better, and the precipitation is likely to be more than that of the same period in normal years. Therefore, the El Niño event is an important climatic background for this widespread freezing rain and snow weather.
So, what is the cause of this rain and snow? **According to Sun Jun, chief forecaster of the Meteorological Observatory, one of the important causes is the superposition of the north and south branch troughs, which opens a "green channel" for the warm and humid airflow to move northward. In the northern hemisphere winter, the mid-latitude westerly wind belt is divided into two branches when passing over the Tibetan Plateau, and the westerly trough on the northern branch westerly jet is referred to as the "northern branch trough", while the westerly trough on the southern branch westerly jet is referred to as the "southern branch trough".
When the two troughs coincide and superimpose during the eastward movement, forming a deep low-pressure trough extending from high latitudes to middle and low latitudes in the central and eastern parts of China, the southwest warm and humid airflow will take advantage of the trend to move northward. However, there is no strong enough cold air in the north to resist, resulting in a steady stream of warm and humid air, which forms snowfall in colder areas and rainfall in warmer areas. Sun Jun said that the overall location of the snowfall and freezing area in this process is northerly, and the rainfall in the middle and lower reaches of the Yangtze River and the south is obvious, and its power should not be underestimated.
What impact will this process have on the Spring Festival? Liu Yanxiang, chief of meteorological services at the Public Meteorological Service Center of the China Meteorological Administration, said that in terms of road traffic, low visibility caused by rain, snow and freezing weather may reduce drivers' ability to predict road conditions. Slippery roads caused by snow and ice can cause traffic jams or congestion. In aviation, low visibility and icy runway snow will also affect aircraft take-off and landing, causing flight delays; At the same time, it is also necessary to pay attention to the impact of aircraft ice causing instability in high-altitude flight.
In terms of railways, in addition to low visibility affecting the driver's judgment of road conditions, snow and ice on the railway may cause the rails to freeze and crack or deform, so it is necessary to be highly vigilant against the potential risk of ice at railway crossings affecting train operation. In addition, railway signalling systems and communication equipment may also be affected. Liu Yanxiang suggested that the public pay close attention to the weather and road conditions, prepare in advance, and make reasonable travel arrangements.
*: China Youth Daily client.