Formation conditions of snowfall How to classify snowfall levels?

We all feel that the weather is getting colder and colder recently, and the temperature has dropped in most parts of the country. At the same time, snowfall occurred in some areas. What are the conditions for snowfall? How to classify the snowfall level? Come and have a look with me.

The formation conditions of snowfall require that the atmosphere contains cold ice crystal nuclei. The maximum amount of water vapor that air can hold at a certain temperature is called saturated water vapor. Below 3.0℃ (freezing point). If the cold air is quite strong and carries moisture, it can snow at the temperature of 1℃ to 10℃. The temperature at which air reaches saturation is called dew point. When saturated air is cooled to a temperature below the dew point, the excess water vapor in the air becomes water droplets or ice crystals. There will be opportunities for snowfall where the climate zone belongs to the middle latitude to the high latitude (that is, the area south of the Tropic of Cancer/north of the Tropic of Cancer), and there will be the same opportunities if there are some mountains or plateaus with terrain above 2000 meters above sea level in the low latitude area.

The standard of how to classify the snowfall level usually refers to the standard of continuous snowfall or the transformation of snowfall into rainfall in a certain period of time. This standard generally adopts two standards: duration 12 hours and 24 hours. Based on the 24-hour precipitation, the precipitation is 0. 1 ~ 2.4 mm for light snow, 1.3 ~ 3.7 mm for small to medium snow, 2.5 ~ 4.9 mm for medium snow, 3.8 ~ 7.4 mm for medium to heavy snow, 5.0 ~ 9.9 mm for heavy snow and 7.5 ~/kloc-0. According to 12 hour precipitation, the precipitation is 0.1~ 0.9mm for light snow, 0.5 ~1.9mm for medium snow,1.0 ~ 2.9mm for medium snow, and 2.0 ~ 4.4mm for moderate to heavy snow, reaching 3.0.

Many places in the country ushered in the first snow after autumn. Recently, affected by strong cold air, the first snowfall since the fall of 202 1 was ushered in many places across the country. 10 On June 6, the National Day holiday, Zhangjiakou, Hebei Province ushered in the first snow in autumn. The Tianlu in Zhangbei Grassland was covered in silver and picturesque. 6543810.6, Tacheng and Yumin counties in Xinjiang ushered in the first snow in autumn. The golden leaves and the white snow flowers set each other off, forming a quiet and beautiful picture. 65438+ 10 9, Zhangye, Gansu, affected by cold air, Shandan Racecourse in the middle of Hexi Corridor ushered in snowfall, and the grassland in late autumn was wrapped in silver. 65438+1October 10, affected by strong cold air, many places in Gansu ushered in the first snowfall since 202 1 autumn. The streets of Pingliang City are wrapped in silver.

Temperature conditions of snowfall Snowfall requires not only that the water vapor temperature is below 3 degrees Celsius, but also other conditions. Water vapor in the atmosphere condenses directly or water droplets condense directly, which is snow. It can also be said that it snows when the temperature in the cloud is too low and small water droplets form ice crystals and fall to the ground or snow. Ice absorbs heat when it melts, so the ground temperature will be lower than when it snows. The atmosphere needs to contain cold ice crystal nuclei. A lot of water vapor. Below 3.0℃ (freezing point). If the cold air is quite strong and carries moisture, it can snow at the temperature of 1℃ to 10℃. Snow is beneficial to the growth and development of crops. Snow is a kind of material with good heat preservation effect, which can protect plants from frostbite in cold winter. The melting of snow water in the next spring can provide a good water supply for vegetation. The power of nature is definitely not a coincidence. Because of the poor thermal conductivity of snow, covering the soil surface with a layer of snow can reduce the diffusion of soil heat and prevent the cold from invading the snow surface.