It is snowing heavily all over the country this year. What caused the cold weather and why?

The most important reason for this abnormal weather is La Nina. Under the influence of La Nina 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. To snow or rain, two conditions must be met: warm and humid airflow (air must have considerable humidity, moisture and relatively high temperature), from the south and tropical regions; 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.