What is causing the severe winter storms across multiple states in the US?

The severe winter storms affecting multiple US states are being caused by a polar vortex that was expected to grip the Rockies and Northern Plains. This weather system moved westward after initially pummeling the eastern US over the weekend, bringing arctic air temperatures and dangerous conditions. The impact has been severe, with at least 14 fatalities reported nationwide, including one death in West Virginia and another in Atlanta, Georgia. The storms have washed out roads in parts of West Virginia and created hazardous conditions across several states, prompting local officials to issue safety advisories as dangerous wind chills continue to affect the impacted regions.