What kind of weather system is behind the cold wave and heavy snowfall?

In the second half of this year, the first cold wave came with the momentum of "big brother", and when it moved east and south, it hit the warm and humid air head-on, and as a result, the warm air stepped on the "brother" and traveled all the way north, and the cold and warm were entangled in a typical "extratropical cyclone" blizzard weather.

Listening to the following song, you may be able to be more calm in the face of a blizzard: "The cold wind is Xiao Xiao, the snow is drifting, the long road is long, and the song is walking. ”

1. The cold wave and cold air of the strong south-frozen northerners

Since yesterday, the temperature in most parts of the north has dropped sharply, and the wind is blowing strongly:

The pink color in the above figure represents an instantaneous gust of more than 8 years, the orange color is more than 10 or more, and the black color is close to level 12, which is much more affected than a typhoon, and the instantaneous wind force in the local area is not inferior.

The result of this strong wind is cooling:

The temperature in the Beijing Plain is only about 3°C:

Riding against the wind this morning gave me numbness.

2. Blizzards under cold waves

Although Beijing is frozen and numb, it is much worse than Inner Mongolia, not only the cooling range and the minimum temperature have been crushed, but also since yesterday in Inner Mongolia's Ximeng, Chifeng and Tongliao have also snowed heavily:

The purple area in the picture above is the area where the rain turns to snow, although the total precipitation is large, but the snowfall is not much for the time being, mainly rain and sleet, and the total precipitation is of course heavy rain in the south, after all, the amount of blizzard 10 mm is also a medium rainfall if it rains.

There should be a lot of photos of wind and snow on the Internet, here are a few photos of the observation equipment in the meteorological observation field:

Weather phenomenon: Chifeng Station took a photo at the zenith at 08 o'clock on the 6th

Snow depth meter: Snow cover conditions at 08:00 on the 6th at Chifeng Station

3. The weather system that causes blizzards - extratropical cyclones

The weather system that caused this blizzard is the same as the North American blizzard that you often hear about, called an extratropical cyclone (some are called winter storms), but the intensity of extratropical cyclones on the continent is generally much weaker than that in North America and Europe. Here's what it looks like on a satellite image:

Visible image of Fengyun 4A at 11 a.m. on November 6, 2023

The cloud system of an extratropical cyclone is very different from that of a tropical cyclone (typhoon, hurricane) with a circular cloud system around the center, often half with clouds and half without it. Stack the isobar diagram to see:

Visible light image of Fengyun 4A at 11 a.m. and sea level pressure at 08 a.m. on 6 November 2023

Because extratropical cyclones are the result of the convergence of warm and cold air – Tai Chi Yin and Yang, while the most typical tropical cyclones are produced in a single warm and humid tropical air mass – with yang and no yin. Of course, there are also Taiji yin and yang typhoons, as mentioned above, autumn typhoons in the South China Sea, and typhoons degenerate after bypassing the subtropical high and entering the westerly wind belt.

Fourth, the three-dimensional convergence of cold and warm air currents of extratropical cyclones - warm air walks on the "brother".

In fact, the image above is only part of the simplest two-dimensional planar image that gives the intersection of warm and cold in an extratropical cyclone, and the full picture in three dimensions is much more complex. Here's a quick look at the most important part of the warm, humid updraft in the 3D image, which is the key to the formation of blizzards.

Let us recall that the extratropical cyclone was formed and developed: at 08 o'clock on the morning of the 5th, the cold wave moved from the northwest to the east and south, and the southwest warm and humid airflow rushed to the north of the mainland, and the cyclone was "rubbed" out in this way.

Low-altitude wind at an altitude of about 1,500 meters at 08:00 on November 5, 2023

Combined with the temperature and humidity field, we know that this is a confrontation between cold dry air from the continent and warm and moist air from the ocean:

Air temperature at an altitude of about 1,500 m at 08:00 on November 5 (left) and total water vapor content in the wind field and atmosphere (right)

With the cold wave to the southeast and the warm and humid airflow to the northeast, the convergence intensified and the cyclone development also moved eastward, and by 20 o'clock on the 5th, its center came from Henan to Liaoning, as shown in the following figure:

Low-level winds at an altitude of about 1,500 meters at 20:00 on November 5, 2023

If we extend the field of view from low altitude to mid-altitude altitude of 3 km, 5 km, and 10 km, we will see that this rotation center is actually tilting and changing towards the northwest, that is, the side of the cold zone:

Wind at an altitude of about 3,000 meters at 8 p.m. on November 5, 2023

Medium-altitude wind at an altitude of about 5,000 meters at 20:00 on November 5, 2023

High-altitude wind at an altitude of about 10,000 meters at 20:00 on November 5, 2023

The complete cyclone structure is only in the lower layers, and in the upper layers, it is manifested as an upper-level cold vortex, and warm air will go up when it is swept into the center of the cyclone, as shown in the conceptual diagram below:

The above figure uses different colors to represent the different climbing heights of the northbound warm and humid airflow, and also depicts its rotation and eastward outflow of the upper layers, which rise very slowly before coming to the vicinity of the cyclone center, and if there are no convection conditions, there will be no strong precipitation or even no clouds, and after coming to the vicinity of the cyclone center, it rises sharply, the upward movement is strong, the clouds are thick, and the precipitation is large, and the temperature is relatively low when you step on the cold air (stepping on the "brother" and walking) below, so the landing is snow, so the blizzard weather comes out. You can use the cloud map to experience this updraft and related cloud systems.

Finally, please pay close attention to the weather forecast and related precautionary interpretation of the meteorological station, the wind and cold wave and snowstorm are really not a joke.

Schematic diagram of cold wave weather