(AP Photo/Timothy D. Easley)] Elsewhere, the weather service said wind chill temperatures as low as -45.6C were expected in most of North Dakota, which remained under an "extreme cold warning," along with large parts of South Dakota and Minnesota.
Extreme weather and life-threatening cold temperatures are set to hit western states near the Rocky Mountains - after severe flooding killed at least 10 people in the eastern US over the weekend.
The polar vortex is a large area of low pressure and cold air surrounding both of the Earth's poles and refers to the counter-clockwise flow of air that helps keep the colder air near the poles.
It also said that "a bitterly cold air-mass containing dangerous wind chills temperatures looks to stretch from the Great Plains to the northeast" - and that there is "high confidence for widespread, record-breaking cold" in the central states.
The National Weather Service's (NWS) weather prediction centre said a winter storm tracking from the Central Plains to the Mid-Atlantic is expected to strike later this week.
