Why do temperatures in US cities change so quickly?

Saw that Dallas, Texas it will be 26 degrees Celsius, then two days later it will only be 9 degrees Celsius. Not sure if that’s normal but that’s a drop in temperature

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The polar vortex is a large area of low pressure and cold air surrounding the Earth's North and South poles. The term vortex refers to the counter-clockwise flow of air that helps keep the colder air close to the poles. Often during winter in the Northern Hemisphere, the polar vortex will become less stable and expand, sending cold Arctic air southward over the United States with the jet stream (right globe). NOAA