(CNN) — A major winter storm and cold snap will affect nearly every US state, bringing what the National Weather Service calls a “once-in-a-generation event” that will bring travel to a standstill on some of the busiest days of the year.
The strengthening storm will bring more than 12 inches of snow and possible blizzard conditions to the Midwest, as the weather service warns of wind chills that threaten the lives of millions of people.
More than 90 million people are under winter weather alerts and more than 87 million are under wind chill alerts. The alerts stretch across 37 states and dip as far south as the Texas-Mexico border.
The wind chill, which indicates how the wind feels, could be between 10 and 20 degrees Celsius below zero, according to the weather service.
“The wind chill of this magnitude can cause frostbite in less than 5 minutes if precautions are not taken, hypothermia also being possible due to prolonged exposure to cold,” the weather service warned Tuesday.
The cold will hold through Christmas weekend, making this the coldest Christmas in about 40 years for parts of the Plains and Midwest.
The storm forecast day by day
Wednesday: The storm will strengthen over the Northern Plains during the day as heavy snow falls across much of the Rocky Mountains, Northern Plains, and Midwest. Slippery roads will cause travel headaches and airport delays in places like Minneapolis, Omaha and Rapid City.
This system will bring 5 to 9 inches of light, fluffy snow across the region, with “higher amounts just north and west of the Twin Cities,” the Twin Cities weather service office said. While snow will fall steadily across the region, strong winds won’t start until Thursday.
Denver will go from a high of 8 degrees Celsius this Wednesday to a low of minus -25 degrees Celsius this Thursday morning. That would be the city’s coldest day in 32 years, according to the weather service.
Thursday: this thursday will be the most difficult day to travel. The storm will hit the Midwest extremely hard with heavy snow and winds. Western Minnesota will face not only blizzard conditions, but also life-threatening wind chills Thursday and Friday.
“Blackout conditions are expected during that time and travel becomes very difficult or impossible,” the weather service said. “This event could be life-threatening if you are stranded with wind chills in the range of -1 to -7 degrees Celsius.”
Chicago could also face blizzard conditions with winds up to 50 mph, with 2 to 4 inches of snow forecast.
“Overall, concern continues to grow over the rapidly developing hazardous conditions Thursday afternoon with potentially significant impacts on peak travel overnight,” the Chicago weather service office warned.
Additionally, high winds can down power lines in the Midwest, especially in areas where heavy snow fell last week that is already downing tree limbs.
Snow could fall as far south as Jackson, Mississippi, Memphis and Nashville in Tennessee and even Birmingham, Alabama on Thursday. Little to no accumulation is expected for most southern cities, however Nashville could accumulate around an inch of snow.
In anticipation of what could be a nightmare week for travelers, United, American, Delta, Southwest and Jet Blue have issued travel waivers for dozens of airports across the country, from the South to the Northeast, because in addition to the With snow covering the roads, low visibility could make air travel dangerous.
Friday: The storm is expected to become a “bomb cyclonic” Thursday afternoon through Friday. A bomb cyclone is when a storm rapidly intensifies and drops 24 millibars (a term used to measure atmospheric pressure) in 24 hours.
The storm is expected to reach pressure equivalent to a Category 3 hurricane when it reaches the Great Lakes, with the weather service describing the force of the downpour as a “once-in-a-generation” event.
“This is a case where snow totals may not tell the whole story. Even small amounts of snow, when combined with very strong wind gusts and plunging temperatures, can cause poor visibility and slippery patches on roads. The sudden arrival of these conditions can increase the danger,” the weather service explained.
The storm will be over the Great Lakes this Friday and will continue to produce heavy snow across much of the Midwest. Parts of Michigan could accumulate more than 12 inches of snow by Friday, making travel impossible.
Heavy rain will also cover much of the I-95 corridor, adding to travel issues and long airport delays.
Even in places where the snow has ended, strong winds will continue to blow at 30 to 40 mph across much of the Midwest and into the Northeast.
From this Friday night through this Saturday morning, New England will receive a snapshot of snow and wind conditions.
a threatening cold
Places that will escape the snow, will not escape the cold. Areas from eastern Montana to the Dakotas will experience the coldest air beginning this Thursday morning. Temperatures will be 40 degrees below normal for these locations. The combination of cold temperatures and windy conditions will send freezing winds down to minus 45 degrees Celsius.
Rapid City will feel like minus 42 degrees Celsius this Thursday morning. By this Friday morning, Chicago’s wind chill will bottom out at minus-zero.
“Dangerously cold wind chills could cause frostbite on exposed skin in as little as 5 minutes,” the weather service office in Bismarck warned.
Even the South will be dangerously cold. Nashville and Atlanta’s wind chill will drop to minus 23 degrees Celsius this Saturday morning and Birmingham will feel minus 20 degrees Celsius.
Georgia Governor Brian Kemp declared a state of emergency on Wednesday due to upcoming “record low temperatures” across the state, with icy winds near zero or negative digits by noon this Friday.
The declaration will help “ensure that essential supplies, especially propane, can be delivered for both commercial and residential needs,” the governor told reporters.
“Communities across the state are about to see temperatures they haven’t experienced in a decade or more,” Kemp said.
The state will pre-treat roads and bridges in anticipation of inclement weather and officials urged residents to avoid travel if possible.
Kentucky Governor Andy Beshear has also declared a state of emergency, with wind gusts expected to reach 40 to 50 mph this Friday and freezing temperatures of minus 23 to minus 32 degrees Celsius expected this Saturday. Beshear asked residents to stay off the roads and have a backup heat source.
Jackson and Birmingham will experience more than 80 hours below zero between Friday and Monday. Houston could remain below freezing for 46 hours between Thursday and Saturday.
The low temperatures will continue through the Christmas weekend, before finally moderating next week.
A “bomb cyclone” in development
So far, snow has fallen mainly in parts of northern and central Montana, northern and central Idaho, eastern Oregon, western North Dakota, central South Dakota, and western Colorado.
The storm, which is expected to become a bomb cyclone, is forecast to strengthen rapidly as temperatures drop sharply across most of the US later in the week.
For a storm to be defined as a bomb cyclonic, it must drop 24 millibars (a measure of atmospheric pressure) in 24 hours.
These storms are more typical of winter nor’easters. But in this week’s case, the bomb cyclone is expected to occur on the Plains, where there is an extreme temperature difference between the warm, moist air preceding the storm and the arctic air mass moving from Canada behind. her.
The storm is expected to reach pressure equivalent to a Category 2 hurricane upon reaching the Great Lakes, with the weather service describing the force of the downpour as a “once-in-a-generation” event.
“This is a case where snow totals may not tell the whole story. Even small amounts of snow, when combined with very strong gusts of wind and plummeting temperatures, can cause poor visibility and slippery areas on roads. The sudden arrival of these conditions can increase the danger,” explains the meteorologic service.
In addition, strong winds can bring down power lines from the Midwest to the Northeast, especially in areas where heavy snow fell last week and is already weighing down tree limbs.
CNN’s Ray Sanchez, Caroll Alvarado, Michelle Watson, Sharif Paget, Devon Sayers, Amanda Musa, Leslie Perrot, Pete Muntean and Robert Shackelford contributed to this report.