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 precipitation forecast map from January 31 to February 5, and you will see a tense color.
According to the latest news from the ** Meteorological Observatory, from January 31 to February 5, the central and eastern regions of China will encounter the largest and longest rain and snow weather process since this winter, and it will also be the strongest rain, snow and freezing weather in winter since 2009. In view of its causes, impacts, responses and other issues of public concern, Sun Jun, chief forecaster of the ** Meteorological Observatory, gave a comprehensive interpretation.
The characteristics of the first question: wide range, long time, complex phase of rain and snow, and certain extremes
*The Meteorological Observatory predicts that the process from January 31 to February 5 will basically cover the entire central and eastern regions, of which the eastern part of Northwest China, North China, Northeast China, and northern Huanghuai will be dominated by snowfall, and most areas in the middle and lower reaches of the Yangtze River and south will have moderate to heavy rain, and some areas will have heavy rain. However, the central and southern Huanghuai, Jianghan, western and northern Jianghuai, northwestern Hunan, and central and northern Guizhou, which are sandwiched between the two forces of rain and snow, will have complex changes in rain or sleet turning to snow.
As far as snow is concerned, in the next 6 days, there will be heavy snowfall, localized heavy snowfall or extremely heavy snowfall in parts of eastern and southern Shaanxi, southern Shanxi, southern Hebei, Henan, Shandong, Hubei, northwestern Hunan, eastern Guizhou, eastern Liaoning, and eastern Jilin, with a cumulative snowfall of 10 mm to 20 mm, and locally more than 30 mm. Among them, the daily precipitation or cumulative precipitation in eastern Liaoning, southern Hebei, southern Shanxi, southern Shaanxi, Shandong, Hubei, Anhui, Jiangsu, northern Jiangxi, northern Hunan, eastern and northern Chongqing will be close to or exceed the same period in history.
From the perspective of freezing rain, this will be the most freezing rain in provinces since this winter: from February 1 to 4, there will be freezing rain in southern Henan, central and western Hubei, northern Anhui, northern Jiangsu, southern Shandong, northwest Hunan, eastern Guizhou, eastern Chongqing and other places.
During this period, the southern region will also be accompanied by a wide range of thunder and lightning weather.
The second question is the cause: the north and south branch troughs echo each other, opening the channel for the warm and humid airflow to the north
One of the important causes of the rain, snow and freezing weather 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, a deep low-pressure trough extending from the high latitudes to the middle and low latitudes will form in the central and eastern parts of China, and the southwest warm and humid airflow can take advantage of the northward trend.
However, there is no strong enough cold air in the north to resist - the weak cold air from the south from January 31 to February 1 can only travel to the middle and lower reaches of the Yangtze River at most.
As a result, from January 31 to February 5, a clear water vapor "artery" runs through the central and eastern parts of China on the weather map, continuously transporting warm and humid airflows, forming snowfall in cold areas and rainfall in warm areas. In addition, a strong Jianghuai cyclone is expected to form in front of the southern branch trough, which will extract a large amount of coastal water vapor and provide further dynamic lifting conditions for rainfall and snowfall.
The situation in the Jianghuai region is more complicated. It is the place where cold and warm air meet, and the temperature of the south and west sides of the Jianghuai cyclone is different from the north and east sides, which aggravates the complexity and intensity of the phase transition of rain and snow.
It is worth mentioning that this widespread freezing rain is also the result of the superimposed effects of warm and humid airflow and cold air. In the area from Huai to the northwest of Hunan and the eastern part of Guizhou, the ground temperature dropped below 0 due to the infiltration of weak cold air, but at an altitude of 700 hPa, the southwest warm and humid airflow was still controlled, and the temperature was above 0, which also caused the ice crystals in the upper air to melt into rain and then touch the ground into ice when they fell.
Three questions about the impact: Large-scale rain, snow and ice are superimposed on the peak of returning home, so it is necessary to be vigilant against risks and strengthen responses
This year is expected to be the "hottest" Spring Festival in history - according to the Ministry of Transport, the cross-regional flow of people is expected to reach 9 billion during this year's Spring Festival, a record high.
During the Spring Festival, there was a wide range of rain, snow and freezing weather, which was impressive in the early 2008 low temperature rain and snow freezing disaster in the south, and the "overlord" cold wave in early 2016.
The duration, low temperature intensity, and freezing range of this process are not as good as the low temperature rain and snow freezing process in the south in early 2008, and the cold degree is not as good as the "overlord" cold wave in early 2016, or even the cold wave process from January 21 to 23 in the past. The scope and intensity of snowfall in the south of the Yangtze River are also weaker than those in the process from January 21 to 22 this year, but the overall location of the snowfall and freezing areas in this process is northerly, and the rainfall in the middle and lower reaches of the Yangtze River and the south of the Yangtze River is obvious, and its power should not be underestimated: the impact period of rain and snow overlaps with the peak of returning home, and the serious impact areas are mostly in the central and eastern transportation hub provinces; The impact range of freezing rain is large, and there is great harm to the operation of highways, railways and flights. Severe convective weather such as thunder and lightning can also be catastrophic.
Meteorological experts suggest that all localities should make various emergency preparations in advance, strengthen the management of traffic safety and urban operation, remind the public to pay close attention to the forecast and warning information issued by the meteorological department, and arrange travel plans reasonably; Relevant departments in southern Henan, Hubei, northern Anhui, central and northern Hunan, and eastern Guizhou have done a good job in inspecting power and communication facilities. Jiangnan, South China and other places should pay attention to preventing geological disasters that may be caused by continuous rainfall and local heavy rainfall, and need to do a good job in lightning protection.
After February 7, the north-south branch trough will move eastward to the coastal areas of China, and the weather in the northern part of the Yangtze River and most of the areas north of it will become clear, but there may be a certain degree of weak rain and snow in the northern region.
*: China Meteorological Administration's WeChat official account.