Why do extreme weather events such as blizzards and tornadoes often occur in North America?

The most fundamental reason is the weakening of the polar vortex. Why is the polar vortex weakening? Observations have found that an explosive stratospheric warming event recently occurred about 30 kilometers above the North Pole, which in turn caused the polar vortex to weaken. Explosive stratospheric warming is a unique atmospheric movement phenomenon in the stratosphere, which mostly occurs in winter and spring in the northern hemisphere. Its occurrence is accompanied by adjustments in atmospheric circulation. Strong explosive stratospheric warming will cause the circumpolar westerly winds to turn into easterly winds, and the polar vortex will collapse. The polar vortex is an area of ??low pressure and cold air around Earth's north and south poles, surrounded by swirling westerly jet streams. Typically, these winds are strong enough to "hold" the coldest air in the Arctic during the winter, like a rubber band stretched tight to trap the cold air. When the polar vortex weakens and the rubber bands loosen, cold air will spill into mid-latitudes, including the United States. In addition, Canada's blocking high pressure develops strongly, and the high pressure ridge points directly to the Arctic Circle. Meanwhile, Mexico's low trough remains. "One high and one low" built a bridge connecting the Arctic Circle and the southern United States. The cold air moved smoothly from the Arctic Circle south to Texas. After encountering the strong warm and humid air flow from the ocean, large-scale cold air was produced. of rain, snow and freezing weather.