CNN  — 

The bitter cold in Chicago has kept hospitals busy, with doctors at one facility during the brunt of an Arctic freeze treating 50 frostbite victims, including some people who may lose an arm or a leg.

“It’s a horrific situation,” says Dr. Stathis Poulakidas, the head of burn and wound care services at Cook County Health.

Poulakidas works at John H. Stroger Jr. Hospital, a level 1 trauma center, that in a really bad year will see 150 cases of frostbite for the season. He said based on what he has seen thus far, this could be one of those years.

Half of the patients that came in over the past few days are homeless, while others had jobs that kept them out.

Poulakidas said they’ve seen “horrific injuries to feet and hands,” some so severe that some victims may lose limbs.

Frostbite in these extreme conditions can set in as quickly as three to 10 minutes, depending on age or exposure or other factors, such as wet gloves and socks, or even alcohol consumption, he said.

Colder than Alaska in some states

The brutally cold weather that’s held millions in its frozen grip for days was so intense Thursday morning that 11 states in the continental United States hit a temperature lower than the one recorded in Alaska’s northernmost city.

The Dakotas, Minnesota, Illinois, Iowa, Indiana, Michigan, New Hampshire, Wisconsin, New York and Pennsylvania all saw temperatures fall below -14 degrees, according to CNN meteorologist Taylor Ward. That was the temperature in Utqiagvik (also known as Barrow) a town of about 4,400 that sits north of the Arctic Circle.

But the end is in sight. The historic deep freeze that’s killed 16 people will let up by the end of the week, according to CNN meteorologists.

At the cold’s peak Thursday morning, about 7 a.m. ET, more than 216 million people saw temperatures below freezing, including 84 million who dealt with subzero temperatures, CNN meteorologist Dave Hennen said.

By the afternoon, about 30 million people were still under wind chill warnings and advisories – down from a peak of 140 million in the morning.

But the misery will slowly melt away Friday, with a warming trend that could give many Americans thermal whiplash.

“Today is the last of the extreme cold air,” Hennen said Thursday. “Temperatures will rebound quickly over much of the area that saw the extreme cold, creating a yo-yo effect of extreme temperature difference.”

Chicago, for example, will see a temperature rise of almost 75 degrees – from extreme cold of 20-25 below zero to temps in the low 50s on Monday.

And Atlanta, which has shivered in the 20s this week, will enjoy temperatures in the 60s when it hosts the Super Bowl on Sunday.

Chicago may have been hit with ‘frost quakes’

Across the country, the bone-chilling weather has shattered dozens of records.

Chicago came close to breaking its record of 27 below zero when temperatures plunged to 21 below, Hennen said.

But for a while, the Windy City had something other than a negative-41 wind chill to worry about: frost quakes.

A train travels in Chicago as a gas-fired switch heater on the rails keeps the ice and snow off switches.

Some Chicagoans were startled awake Wednesday by a series of large booms, CNN affiliate WGN reported.

“I thought I was crazy! I was up all night because I kept hearing it,” Chastity Clark Baker said on Facebook, according to WGN. “I was scared and thought it was the furnace. I kept walking through the house. I had everyone’s jackets on the table in case we had to run out of here.”

That boom was probably a weather phenomenon known as cryoseism – and dubbed a “frost quake.” It happens when water underground freezes and expands, causing soil and rock to crack.

At least 16 deaths have been linked to this week’s extreme weather.

Ice lines the shore of Lake Michigan before sunrise on Thursday in Chicago.

Eight of those deaths have been in Iowa; four occurred Thursday in traffic accidents during snowy conditions.

Three people died on US 59 in Crawford County when a car crossed into the other lane and hit another vehicle at about 5 a.m., Iowa State Patrol Sgt. Nathan Ludwig said.

A person in Johnson County died in a single-car accident on Thursday afternoon, he added.

Storm-related deaths were also reported in Illinois, Michigan, Minnesota, Indiana and Wisconsin, authorities said.

The cold weather killed a zebra on a private farm near Delphi, Indiana, according to the Carroll County Sheriff’s Office. The zebra had gotten stuck in a metal fence, Sheriff Tobe Leazenby said. Officials consulted a veterinarian, who said the air likely crystallized in the zebra’s lungs, killing the animal.

Mail service is still suspended

The massive cold snap has also frozen some mail and blood donation services.

The US Postal Service said due to arctic temperatures, Thursday deliveries are suspended in parts of Illinois, Indiana, Michigan, Ohio, Pennsylvania and Wisconsin.

Mike Calen, left, and Steve Goyette, right, prepare to tie off as the ice-covered fishing boat  Buzzards Bay  arrives in the harbor in New Bedford, Massachusetts on Thursday.

The American Red Cross said 370 blood drives across the country were canceled as temperatures dropped.

“The Red Cross currently has an emergency need for blood and platelet donors of all types to help ensure lifesaving medical treatments and emergency care are not delayed or canceled this winter,” spokeswoman Stephanie Rendon said in an email.

State government offices in Michigan were closed for a second day on Thursday due to “emergency weather conditions.”

The weather also caused headaches for travelers. More than 2,300 flights involving US airports were canceled on Thursday, the majority of which were due to fly out of Chicago O’Hare International Airport and Chicago Midway, according to FlightAware. More than 3,600 flights from or to US facilities were delayed.

CNN’s Faith Karimi, Steve Almasy, Andrea Diaz, Marlena Baldacci, and Joe Sutton contributed to this report.