Portland’s emergency shelters were filled to capacity Thursday night as dangerous cold drove much of the city’s homeless population indoors.

Margaret Curtis, a meteorologist with the National Weather Service in Gray, said Portland’s low was expected to drop to one degree below zero overnight, the coldest since the temperature in the city dipped to 10 below on Feb. 15. By midnight, the temperature at the Portland International Jetport was 2 above – and the wind chill was minus-20.

Curtis said the wind chill Friday morning will make it feel as though it’s 20 below. It will gradually warm up during the day, reaching a high of about 12 degrees. But Curtis said winds will make it feel like it’s 4 below zero.

Curtis said the forecast calls for snow to start late Friday and continue for most of Saturday before turning to freezing rain Saturday evening. Sunday’s forecast calls for rain and highs around 40 degrees, she said.

“In my line of work, these are the kind of days that I spend a lot of time worrying. It can be a life-or-death thing on the streets,” said Rob Parritt, director of Portland’s Oxford Street Shelter, on Thursday evening. “We will be busy tonight.”

Oxford Street provides 154 beds. When those beds fill up, Preble Street, a social services nonprofit, serves as an overflow location where 75 people can stay – sleeping on mats.

Parritt and another shelter spokesperson said all of the city’s shelters would be at capacity Thursday night.

Parritt said the Oxford Street Shelter would take the unusual step of remaining open all day Friday because of the extreme cold. It usually doesn’t open until 2:30 p.m.

As sea smoke blankets the Atlantic in the background, commuters make their way along Old Orchard Street Friday in sub-zero temperatures. Carl D. Walsh/Staff Photographer

Parritt also ordered his staff to lift restrictions on homeless people who have been banned because of behavior. Provided they are not violent, those people would be allowed to spend the night.

There are several other shelters in the city, including a shelter for women, teenagers and families. Preble Street, a private agency, operates the shelters for women and teens.

“We are trying to work together as a community to make sure that a homeless person has as many options as possible,” Parritt added.

Donna Yellen, chief program officer for Preble Street, said the agency’s Joe Kreisler Teen Center reached capacity Wednesday night. The center has 24 beds. Yellen said the staff brought in cots to accommodate the overflow.

Florence House on Valley Street is a 40-bed shelter for women. When it reaches capacity, women are sent to the Oxford Street Shelter. Florence House exceeded its capacity Wednesday night, according to Yellen.

Yellen said the overflow area at Preble Street would be full Thursday night. During the day, Preble Street “was packed, the need is so great.” Preble Street serves three meals a day to the city’s homeless population.

“Homelessness, especially in these weather conditions, is life-threatening,” Yellen said.

A woman bundled up for frigid weather makes her way up the sidewalk on Factory Island in Saco on Thursday. The temperature was expected to drop below zero overnight. Shawn Patrick Ouellette/Staff Photographer

Yellen said Preble Street’s annual vigil to remember homeless people who have died this year will be held Dec. 21 in Monument Square. The event will start at Preble Street around 4 p.m. with participants marching up Preble Street to Monument Square. In 2015, 43 homeless people died in Portland, the highest number ever recorded.

Shelter workers can’t force a homeless person to come to a shelter, but they have several resources if they find someone in trouble.

“People really look out for each other,” Yellen said. “People who have experienced homelessness are incredibly powerful advocates for each other.”

Roger Goodoak, 63, of Portland is a homeless advocate.

Goodoak, a Vietnam War veteran, said he was homeless for eight years before he sobered up and created a new service – Maine Homeless Veterans Alliance.

“Roger is a very kind and generous person,” Yellen said.

“I drank my way across 50 states,” Goodoak said Thursday evening during an interview in his van, which was filled with blankets and handwarmers. He was heading north to Brunswick to pick up more donated supplies before driving back to Portland.

Goodaak said he planned to spend most of his evening hunting down homeless veterans and others who were still outside and who might need something to keep them warm. He was planning to look for people in alleys, under loading docks and in tents.

“People may not realize this, but there are a lot of places for homeless people to hide,” he said.

Goodoak said he relies entirely on donations. He keeps a supply of hats, gloves, blankets, sleeping bags and tents in a local storage unit.

Temperatures started to plunge Thursday afternoon as a strong Arctic cold front moved across the Northeast. AAA Northern New England spokesman Dan Goodman said the chilly conditions were having an impact on motorists.

Goodman said AAA responded to 250 calls for service between 5:30 and 6:30 p.m., with 70 percent of those calls asking for jump starts or car battery replacements.

“The Portland area has been really busy,” Goodman said Thursday night. Goodman said many motorists don’t realize that when temperatures drop to zero, a battery loses 60 percent of its strength.

He said AAA expects to respond to about 5,000 calls for service Friday morning. That is more than double the 2,000 calls on a typical day in winter.