Recently, the eastern United States has been hit by winter storms. Heavy rain, floods, strong winds and other severe weather have caused at least 13 deaths. This winter storm not only has a serious impact on the lives of local residents, but also has aroused people's attention to the causes of extreme weather. So, how are winter storms formed? Why does North America frequently encounter such weather?
Experts pointed out that the southward movement of the Arctic vortex, the violent convergence of cold and warm air, and the unique terrain conditions in North America have jointly contributed to the ravages of this winter storm. At the same time, global warming is also increasing the frequency and intensity of extreme weather events.
Lin Nan, meteorological analyst at the China Meteorological Administration: Winter storms are essentially temperate cyclones. They are a type of low-pressure vortex center formed in mid- and high-latitude regions. They may appear all year round, but they will be more intense and more frequent in winter. Their appearance is often accompanied by a variety of severe weather such as drastic cooling, heavy snowfall, heavy rainfall, freezing rain, and strong winds, and may also cause secondary disasters such as mountain torrents, landslides, and mudslides.
Lin Nan, meteorological analyst at the China Meteorological Administration: Winter storms are not uncommon in North America. The splitting of the vortex from the Arctic and its southward movement is conducive to the formation of winter storms. There is a counterclockwise rotating vortex over the Arctic, with super cold air inside and a strong westerly jet stream outside. Generally, the westerly jet stream will restrain the cold air, and the greater the temperature difference between the Arctic and the tropics, the stronger this restraining ability. When the Arctic vortex produces unstable disturbances, the vortex boundary expands and sinks toward the equator, it will carry strong cold air southward.
Lin Nan, meteorological analyst at the China Meteorological Administration: From this 500 hPa altitude field situation map projected southward from the Arctic region, it can be seen that there is a deep vortex over the eastern United States to eastern Canada, which is also the key weather system that caused this winter storm. When the Arctic vortex extends all the way south to Canada and the United States, there is strong cold air behind the vortex, and there is strong warm and humid water vapor transport from the Gulf of Mexico in front of the vortex. The violent intersection of cold and warm air is very likely to produce cyclones, thus triggering winter storms.
Lin Nan, meteorological analyst at the China Meteorological Administration: In addition, the unique terrain conditions in North America are also a powerful driving force for the formation of winter storms. The terrain of North America is distributed in a north-south vertical column, with the Appalachian Mountains and the Rocky Mountains running north-south on the east and west sides, and the vast Great Plains in the middle. Therefore, when the strong cold air from the Arctic moves south, it can almost drive straight in, and the sharp drop in temperature will start from Canada and spread all the way south to Texas in the southern United States. At the same time, the vast plain terrain is also conducive to the long-term convergence of cold and warm air, bringing continuous precipitation.
Lin Nan, meteorological analyst at the China Meteorological Administration: In addition, against the background of global warming, the warming rate in the Arctic region is 2 to 3 times the global average, which will weaken the "binding force" of the westerly jet stream on the polar cold air, making it easier for the cold air to move south to the mid-latitudes. The frequency of extreme weather events will also increase accordingly.
