Why is it so cold?

Mr. Yang, chief forecaster of China Meteorological Bureau, said: In winter or early winter, there is less cold air in most parts of China, one is weak and the other is not frequent. Because we all know that the two conditions that snow or rain must meet are warm and humid airflow (air must have considerable humidity, moisture and high temperature), which comes from the south and from the tropical region; Another condition is that there must be cold air, which comes from the polar regions and from the mountainous areas. The cold air affecting our country in the early winter of this year is relatively weak, and the frequency is not much. Even with warm and humid airflow, it is not easy to snow without cold air. Therefore, before 1 month, there was relatively little precipitation, dry air and high temperature in most parts of China. However, in 1 month, great changes have taken place in the atmospheric circulation, making the cold air activities in China more active. After the cold air is active, the warm and humid air flow at low latitudes gradually strengthens, just combining cold and warm. Therefore, during this period, the cold air is relatively strong, the cold air activity is relatively frequent, and the warm and humid airflow is relatively strong. These two air currents have the same influence and meet coincidentally, so recently, especially in the Yangtze River basin, there have been more rain and snow, and the low temperature weather has been maintained for a long time. This is the main reason. There is also the cold front weather caused by the cold air mass formed by the Asian high originating from Mongolia and Siberia. But simply from the perspective of the Asian high and cold front heading south, isn't it a bit one-sided? In that case, there will be low temperature snowfall in eastern China every winter. But how to explain the reason for such a rare large-scale continuous snowfall this year? After thinking, I think the most important reason for this abnormal weather phenomenon is La Nina phenomenon. Affected by La Ni? a phenomenon, the water temperature in the equatorial western Pacific Ocean is high, and the water evaporation increases, which leads to the abnormal meridional circulation in East Asia. In addition, since the spring, the northerly airflow has prevailed in the north of China, while the warm and humid airflow in the southeast is relatively weak. Therefore, cold waves and strong winds frequently appear in the north. We know that at this time, East Asia is being affected by the Asian high. Therefore, it has strengthened the power of Siberian cold air moving rapidly southward. After the cold air passes through the border, the temperature drops sharply, and after being blocked by Qinling and Daba Mountains, it goes south and stays in these areas for a long time. In addition, the warm and humid air flow from the southwest Indian Ocean to the north continuously increases the humidity and interacts with the cold air, thus forming continuous topographic precipitation (snow). Perhaps it caused the recent continuous low-temperature snowfall.