Thousands of antiabortion protesters make their way past the U.S. Supreme Court last year in D.C. for the annual March for Life, to protest the court’s decision to legalize abortion. (Andrew Harnik/For The Washington Post)

D.C. schools will be closed on Friday. The District government will operate under a state of emergency, sending non-essential personnel home at noon. And tow trucks will begin hauling away cars parked on downtown thoroughfares to make room for expected mountains of snow.

But one group — perhaps numbering in the tens or even hundreds of thousands — will be filling the streets around the U.S. Capitol just as others have been told to stay at home. The annual March for Life, which protests U.S. abortion policies, will go on, according to federal law enforcement officials.

The antiabortion demonstration has been held in D.C. without interruption for more than four decades on the anniversary of the 1973 Supreme Court decision in the case of Roe v. Wade.

But this year’s march is the first to coincide with the arrival of a potentially historic snow storm that could dump 24 inches or more on the nation’s capital.

The federal permit required for the march to take place could be withdrawn under a provision that prevents gatherings in D.C. during severe weather events.

But U.S. Park Police spokeswoman Sgt. Anna Rose said that as of Thursday afternoon, representatives of federal and local law enforcement agencies had agreed to tread lightly and allow the event to go on because the bulk of the snowfall is expected overnight Friday into Saturday.

“As of this moment, it’s on,” Rose said. “This is a First Amendment event, and if people want to come and demonstrate, we want them to be able to come say what they have to say.”

Rose said authorities have only once in recent years stopped a First Amendment demonstration. In that event at the federal law enforcement memorial, an intense thunderstorm prompted police to clear the public plaza.

Not everyone is endorsing the march continuing, however. At a news conference Thursday morning, D.C. Mayor Muriel E. Bowser (D) declined to say directly whether she thought that the event should go on.

“We’re watching it very closely,” she said. “I would ask that organizers make good decisions for their participants.”

Jeanne Mancini, president of the March for Life Education and Defense Fund, said organizers are doing just that.

“We are not forcing anyone to come, we are encouraging everyone to do what they think keeps them safest,” including watching the event at home on television.

But Mancini said organizers were adamant about continuing. “For those who have marched for the last 42 years on the anniversary of Roe v. Wade, we want to provide that opportunity to continue doing so.”

More than 1,000 teenagers and young adults already in town from as far away as California and Canada gathered at a D.C. hotel for an indoor pre-rally on Thursday.

Mancini said she could not predict how many people would turn out on Friday, but she acknowledged the event would be smaller, with several groups that were planning to travel long distances by bus contacting organizers in recent days to say they would not make it this year.

Mancini said that despite the comments from Bowser, organizers had not felt discouraged from continuing. A rally is scheduled at noon, the march at 1 p.m., and a final ceremony will take place at 3 p.m. in front of the steps of the Supreme Court. By that time, snowflakes will likely be falling in the District, and an expected early evening rush hour could be in full swing.

“We have worked very closely with police, we have emergency plans and weather plans, we think that is in the best interest of everyone that we continue,” Mancini said. “We haven’t received any negative feedback from police.”