The polar vortex is sending temperatures plummeting in the US Midwest and Northeast this weekend, says the National Weather Service.
Millions of Americans in more than a dozen states from the Great Lakes to New England are under wind chill advisories or warnings.
Wind chills are expected to drop below -30F (-34C) by Saturday night, with gusts to reach 45mph (72kph).
Forecasters predict as many as 15 cities in the Northeast, including Boston, Philadelphia and Washington DC, could see record lows on Sunday, Valentine's Day.
It is the third winter in a row that the polar vortex - an icy blast of air from the North Pole - has punched southward into the US.
The National Weather Service said: "An eddy of the polar vortex over Quebec, along with a reinforcing cold front, is expected to bring the coldest weather of this winter season from the Great Lakes to New England.
"Wind chill warnings and lake effect snow warnings are in effect for these areas, with wind chill readings dropping below -30 degrees by Saturday night.
"Actual temperatures will also be frigid with highs in the single digits and teens, and subzero lows across much of upstate New York and New England."
The cold has already been blamed for a reported three deaths in a pile-up involving more than 50 vehicles in Pennsylvania on Saturday.
Emergency services battled snow and freezing temperatures to reach multiple casualties at the scene on Interstate 78.
State police said weather was probably a factor in the crash, reports PennLive.
New York City Mayor Bill de Blasio has warned city-dwellers to heed the weather warnings and take "extreme precautions" over the weekend.
He urged residents to check on vulnerable family members, friends and neighbours.
"Extremely cold weather can be life-threatening, especially for seniors, infants and people with medical conditions," he said.
He said homeless people would be brought by city workers to shelters or hospitals.
The cold has forced organisers to cancel an ice festival on Saturday in Central Park.
Racing officials have also cancelled all meetings at New York's Aqueduct Racetrack.
Apart from the odd snow flurry in the nation's capital on Saturday morning, the region is not expected to see a repeat of last month's blizzards.
NOAA Monitors the Stratosphere
NOAA monitors meteorological conditions and ozone amounts in the stratosphere. On this page we present graphics to aid in visualizing the evolution of the South Polar "ozone hole" and factors important for ozone depletion in the polar areas. Several other web pages (see links) discuss the processes of ozone depletion. Here we provide information on the size of the polar vortex, the size of the ozone hole, the size of the area where air is cold enough to form Polar Stratospheric Clouds (PSCs), and which parts of this cold air are sunlit such that photo-chemical ozone depletion processes can occur. In addition, the latitudinal-time cross sections shows the thermal evolution at all latitudes.
- Ozone Hole Size
- OMPS and SBUV/2 Total Ozone Southern Hemisphere Analyses
- Erythemal UV Daily Dosage Estimate
- South Polar Vertical Ozone Profile
- Time Series of Size of S.H. Polar Vortex
- Time Series of Size of S.H. PSC Temperature
- Time Series of Size of N.H. Polar Vortex
- Time Series of Size of N.H. PSC Temperature
- Time Series of Eddy Heat Flux towards the South Pole at 100 mb
- Time Series of Eddy Heat Flux towards the North Pole at 100 mb
- Temperature at 50mb Latitude vs Time Contour Plot
- S.H. Tnat and Tice Pressure vs Time Contour Plot
- N.H. Tnat Pressure vs Time Contour Plot
- Temperature over the South Pole Height vs Time Contour Plot
- Links to Additional Stratospheric Information
