CHICAGO • Forecasters are sending chills down some spines, with a prediction that much of the northern half of the United States could see frigid weather next week similar to life-threatening lows the polar vortex brought to parts of the country in 2014.
Anticipation of a freezing blast began to build this week when weather maps and forecast models showed similarities between next week's system and the one that developed in January 2014.
The polar vortex is an area of low pressure - a wide expanse of swirling cold air - that is parked in the Earth's polar regions.
The southward shift in the polar vortex in 2014 brought the American Midwest some of its coldest weather in two decades.
Icy conditions snarled travel and thousands of flights were cancelled or delayed. Frigid temperatures, combined with gusting winds, created life-threatening wind chills as low as minus 51 deg C that killed at least nine people.
The coldest weather next week is expected in the Midwest and northeastern US states starting around Tuesday, according to forecasts that show temperatures in the single digits in some cities.
"The air mass on the way for the middle of December is likely to be substantially colder when compared to that of this past week and this weekend," AccuWeather meteorologist Paul Pastelok wrote on Thursday.
US broadcaster The Weather Channel said: "Winter storm warnings have been issued for the Portland, Oregon, metro area, while Seattle has been placed under a winter weather advisory. This means significant amounts of snow, sleet or ice are expected, which will make travel hazardous."
From the Northern and Central plains to wide swathes of the Midwest, temperatures are likely to drop drastically this week, according to AccuWeather.
It is unclear how far south the cold air will be felt, said Mr Pastelok.
Chicago, the largest city in the Midwest, is bracing itself for temperatures in the teens next week, according to an AccuWeather forecast, which showed a low of minus 8 deg C forecast for next Wednesday and Thursday.
Further north in Minnesota, Minneapolis-St Paul NBC affiliate Kare forecast temperatures dropping to minus 12 deg C next Tuesday, then minus 13 deg C next Wednesday.