What is causing dangerous temperature drops across the southern United States?

A polar vortex is pushing temperatures down to dangerous levels across the southern United States, extending as far south as the Mexico border. This extreme weather phenomenon has triggered cold advisories affecting more than 87 million people throughout 22 states. The severity of this cold snap is unusual for southern regions, creating hazardous conditions that require special attention from residents and authorities alike. The widespread nature of these extreme cold advisories highlights the significant impact of this weather system on a substantial portion of the country.