Under what circumstances can it snow heavily?

◆ Water vapor condition is very important for the formation of heavy snow.

The better the water vapor condition, the bigger the snowflake will be. We know that the water vapor conditions in the air in the middle and lower reaches of the Yangtze River are much better than those in the middle and lower reaches of the Yellow River. Often cold air goes south, and the range and quantity of snowfall are larger than those in the northern region with low humidity. Sometimes it snows all over the sky, which is spectacular and even reaches the level of blizzard. 1955 1 In Shouxian County, Anhui Province and Nanjing, Jiangsu Province, a heavy snow once reached 52 and 5 1 cm.

◆ Strong cold air process is easy to form heavy snow.

If it's not cold, it can't snow. Otherwise, even if there is snow in the sky, it will melt in the air because the temperature is higher than 0℃ and land in the middle and low altitude in the form of rain. Every year, due to the early influence of cold air in the north, there is snowfall in the north first. However, we know that clouds are places where snowflakes are bred, and large-scale deep clouds are places where large-scale snowfall is bred, and those persistent cold waves or strong cold air going south provide temperature conditions for heavy snow and even local snowstorms. Strong dry and cold air lifts a wide range of warm and humid air to the condensation height, forming wide and deep clouds, which often leads to the spectacular scene of heavy snow and white clothes wrapped in Wan Li from north to south in China.

However, many articles have pointed out that when the temperature is below 0℃ and close to 0℃, the merging ability of snowflakes is particularly great, and it is easy for multiple snowflakes to connect with each other to form larger snowflakes and land in the form of wet snow. This statement further shows that "goose feather and heavy snow" is neither a patent in high latitude cold areas or high altitude mountainous areas, nor a patent in the severe winter of 65438+ 10.

When China is in a cold cycle, such as 1950s and 1970s, it is very normal for large-scale snow to form, not only in the north, but also in the middle and lower reaches of the Yangtze River. Since 1980s, China has turned into a warmer cycle, but it does not mean that there is no strong cold air in a specific year of the warmer cycle. As long as there is stable strong cold air invading our country, even in the late autumn and early winter of 165438+ 10, there will be heavy snow weather, such as the heavy snow process in several northern provinces and cities on June 6-7, 2003.

◆ The lower the temperature, the smaller the snowflake.

The size of snowflake crystals is closely related to the temperature at which water vapor condenses and crystallizes. The colder the weather, the lower the temperature and the smaller the snowflake crystal. When the weather is very cold, the diameter of snowflake crystals formed is often less than 0.05 mm. Meteorologists have observed that prismatic ice crystals will form when the temperature is between -8℃ and -5℃. When the temperature is -5℃ to -3℃, needle-like ice crystals are formed; When the temperature is -3℃ to 0℃, thin hexagonal plate-like ice crystals are formed. It can be seen that when the temperature is -3℃ to 0℃, the shape of snowflake is the largest and most complete. Snowflake crystals formed in very cold weather are so small that they are almost invisible to the naked eye. Only when they shine in the sun can people find them as fine powder. This kind of snow is called dry snow.

◆ Heavy snow is not a patent in alpine regions.

Since 1980s, China has been in a warming cycle, and heavy snow with goose feathers is rare in many areas. In people's imagination, it seems that the hometown of "goose feather and heavy snow" is only in the cold area with high latitude and the alpine area with higher altitude in winter. When describing the cold in winter, we sometimes like to describe it as "goose feather and heavy snow". When it comes to goose feather and heavy snow, people often think of the Linhai Snowfield in the northeast, which seems to be the product of cold areas at high latitudes, but in fact, the colder it is, the easier it is to form. Here, we will not elaborate on the specific formation process of snowflakes, but only talk about the related factors that form heavy snow. In recent years, some scientists have found that the crystal form of different snow and the size of snowflakes depend on the air temperature and the amount of water vapor.

◆ Snowflakes fuse many times to form snowflakes.

The so-called goose feather snow is actually not a piece of snowflake. Snowflakes fall from the clouds to the ground, and the journey is very long. Multiple snowflakes are easily attached to each other and blended together. This kind of snowflake, which is made up of many snowflakes stuck together or even fused many times, is what we call goose feather snow. The diameter of a single snowflake crystal we see falling from the sky is generally 0.5 to 3 mm, but the largest diameter of snowflake formed after many times of merger can reach about 15 mm.