The "goose feather snow" in Beijing has exploded the circle of friends, but why is the snowfall only 1 mm?

On February 12, it finally snowed in Beijing, which exploded the circle of friends.

However, from the meteorological professional point of view, this snowfall can only reach a light snow level of one millimeter. Why does this little 1 mm snowfall explode the circle of friends?

This leads to a professional question: how is the snowfall measured?

Meteorologically speaking, snowfall refers to the value measured by meteorological observers in millimeters after the snowflakes collected in 12 hours or 24 hours are turned into water in standard containers.

It can be seen that a place with a 24-hour precipitation of 0. 1~2.4 mm is classified as light snow, and the snowfall of 1 mm is only at a medium level in the light snow magnitude.

But don't underestimate that this little 1 mm, 1 mm rain may not feel anything on the ground. Maybe sometimes the ground won't be slippery, but the snowfall of 1 mm is enough to make the roof white.

What is the concept of 1mm snowfall?

In order to let people feel this 1mm intuitively, we also want to introduce another professional name in meteorology, "Snow Depth".

Usually, people see if it snows. First, they look at whether there are snowflakes floating in the sky, and then they look at whether objects such as the ground have turned white, and how thick the snow is when they crunch on it.

The depth of snow is the thickness of snow we usually see. It is the vertical depth from the snow surface to the ground, usually in millimeters. It is a value that changes constantly with the increase of snowfall.

So what does 1mm snowfall mean?

Usually, how much snow can be accumulated by 1 mm snowfall has a great relationship with factors such as ground temperature and water content in snow. If the ground temperature is high, the snow will melt as soon as it falls to the ground and will not form snow.

The water content in snow will also directly affect the depth of snow. If the water content is high, the snow is thin, and if the water content is low, the snow depth is deep.

Our intuitive feeling is that some snow is easy to pinch together in our hands, and it is easy to make a snowman, while some snow is particularly easy to disperse even if it is pinched hard, and it is relatively difficult to make a snowman, which is related to the water content in the snow.

Now we assume that the ground temperature is low and all the snow falls to the ground, so how much snow can be accumulated by 1 mm snowfall?

Usually, the water content of snowfall in the north is smaller than that in the south. 1mm of precipitation is equivalent to 8 ~ 10mm of snow in the north, and 6 ~ 8mm of snow in the south. The snow in the north is looser than that in the south.

According to the Central Meteorological Observatory, from 00: 00 on 12 to 04: 00 on 12, the average snowfall in Beijing was 0.5 mm, the average snowfall in urban areas was 0.6 mm, and the maximum snowfall was 3.0 mm in Erhaituo, Yanqing. The average city is only 0.5 mm, but the ground in many parts of Beijing has turned white, and the snow in many places is quite thick.

Reference: Popular Science China.