At 14:47 on February 20, 2024, the Shanxi Provincial Meteorological Observatory upgraded and issued an orange warning for blizzard, warning areas: southeast of Xinzhou, Taiyuan, Luliang, northern Linfen, Jinzhong, and Yangquan. More than 10 mm of snowfall is expected in the warning area in the next 6 hours.
As soon as the early warning manuscript was released, many netizens questioned it in the background
To tell you the truth, when I first saw the warning message, I was puzzled: didn't it say "Blizzard"? Why is it only 10 millimeters? It's not as thick as the sole, is there a mistake?
Could it be that the meteorological department made a mistake? Of course not! After many searches and inquiries, the meteorological department was finally returned a "clean slate".
First of all, we need to figure out, how are the snowfall levels divided?
The snowfall level is not based on the thickness of the snow on the ground. According to the standards of the meteorological department, the amount of snowfall varies from low to high depending on the size and shape of the snowflakes that fall to the ground, and the density of the snow.
Light snow: Less than 1 snowfall in 12 hours0 mm (equivalent to the amount of rainwater after melting, the same below).
Moderate snow: 10～3.0 mm or 2 snowfall in 24 hours5～5.0 mm.
Heavy snowfall: 30～6.0 mm or 5 snowfall in 24 hours0～10.0 mm.
Blizzard: More than 6 snowfall in 12 hours0 mm or more than 10 snowfall in 24 hours0 mm.
Heavy Blizzard: 20 snowfall in 24 hours0～30.0 mm of snowfall process.
Heavy Blizzard: A snowfall of more than 30 mm in a 24-hour period.
For those who are dazzled by the above numbers, please continue to look below:
What does 1mm of snowfall mean?
Let's be clear here: the amount of snowfall does not equal the thickness of the snow!
The average ratio of snow depth change to the corresponding snowfall in winter is 07 cm mm, that is, an average of 1 mm of snowfall corresponds to an increase in snow depth of 07 cm. However, this ratio is affected by the temperature, and the lower the temperature for the same amount of snowfall, the greater the increase in snow depth.
What will a 10mm blizzard bring?
1 mm of snow may not be a big deal, but knowing the relationship between 1 mm of snow and snow depth, we can speculate about the impact of a snowstorm of more than 10 mm.
Blizzards mostly occur in the long and cold winter in northern China, due to the low temperature, dry snow is the majority, and the corresponding ratio of snow depth increment to snowfall is about 09～1.2 cm mm, then more than 10 mm of snow means more than 9 cm of snow.
Maybe for pedestrians, 10 centimeters of snow just below the surface of their feet can walk, but for cars, it is much more dangerous. It is important to know that the coefficient of friction of a dry pavement is usually 06 or so, and the friction coefficient of the road surface with ice and snow will drop sharply to 01 - 0.2 or so, this will greatly reduce the adhesion of the road surface, the stability of the car steering and braking decreases, it is difficult to control, it is easy to slide left and right, and the braking distance increases, and the driving safety is greatly threatened.
Now, I finally know why a snowfall of more than ten millimeters can be called a blizzard
In addition, when traveling in snowy days, please pay attention to safety and drive slowly!
The content is synthesized from China Weather Network and CCTV Network.