Why is the precipitation of a heavy snow almost as small as that of moderate rain?

Are they big, too?

The difference in precipitation seems a little big? ?

Friends who are familiar with the weather forecast should be no strangers. When forecasting summer rainfall, the painting style is often like this:

"There is heavy rain somewhere, and there is heavy rain locally (100 ~120mm)."

When it comes to forecasting snowfall, there is a sudden change in painting style.

"There is heavy snow (5 ~ 8 mm) in some areas."

The same prefix is "big", and the feeling of going down to the ground is not small, but the difference in precipitation seems to be a bit big. Why?

The principle of precipitation is the same, and the landing form is different.

To find out why there is such a big difference between rain and snow precipitation, we must start from the source of rain and snow.

Whether it rains or snows, the basic principle is the same, but the state of precipitation falling to the ground depends on the specific weather conditions.

Near-surface temperature is a key factor to judge whether there is snowfall or rainfall.

Take the snowfall conditions in Anhui as an example: when the near-surface temperature is higher than 2℃, it is generally rainy, and when the near-surface temperature is lower than 2℃, it is generally snowy.

At the same time, the temperature distribution at high altitude is also very important.

If the near-surface temperature is above 2℃, but the high-altitude temperature is very low, and the snowfall has not melted into raindrops before reaching the ground, it is still snowfall rather than rainfall. If there is a melting layer at an altitude of 3000 meters, the ice crystals and snowflakes in the high-altitude clouds will become supercooled water droplets below 0℃, and will form freezing rain when they touch branches, wires, hay or other ground objects.

The snow depth and precipitation are roughly 10: 1.

The public's perception of snowfall depends largely on the thickness of snow. Here, the answer is obvious: the same water is much denser as rain than as snow. Therefore, the actual precipitation of heavy snowfall is much less than that of the same level.

If the process of snow melting is not considered, the relationship between snow depth and precipitation is about 10: 1. For example, there is 10 mm snow in a certain place, but the actual local precipitation is actually only1mm.

The precipitation is the same, but the depth of snow varies from place to place.

The correspondence of 10: 1 mentioned above is under ideal conditions. But everywhere, this correspondence is not exactly the same.

The water vapor condition in the north is not as good as that in the south. Cold air is in a dry and cold state, and precipitation will only occur when dry cold air meets wet and warm air. There may be deep snow in some parts of the north, but the snow is often accumulated by multiple snowfalls. There is no shortage of wet and warm air in the south, so it usually snows heavily. The snowfall of 20 mm is a "small case" in the south.

As far as the nature of snow is concerned, the difference mainly lies in the water content. In the north, snowflakes are usually big, like goose feather snow, but the water content is not high. It is usually wet snow in the south, with small shape but high water content, and the snow is in a "compacted" state. Therefore, in the south, the precipitation of 10 mm may be less than 10 cm.