What is the Polar Vortex?

What's a polar vortex? - Vox

Analysis: Polar Vortex collapse causes heavy winter for North America and the Nordics - Kjeller Vindteknikk

The polar vortex is coming—and raising the odds for intense winter weather

Polar Vortex Causes Midwest States Of Emergency As Cold Pushes Farther South : NPR

What is the polar vortex?

What is a polar vortex? What to know about the weather phenomenon

The polar vortex, briefly explained - Vox

Polar vortex - Wikipedia

Brief visit from polar vortex to bring record-challenging cold to Northeast