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It’s Tuesday. We’re off tomorrow for Christmas and back on Thursday.

Weather: Sunny, breezy and a little warmer than usual, with a high that could reach the upper 40s or even 50. Christmas Day: Still sunny but a bit cooler.

Alternate-side parking: In effect today. Suspended tomorrow for Christmas.

The Times’s Matthew Haag reports:

Pedestrians in New York City are usually aware of the dangers by their feet: cars, bicyclists, sidewalk grates.

Increasingly, a threat may be coming from above: ice falling from a building’s facade.

The danger is not new: The police warned of “falling ice slabs” from Manhattan towers in 1939. But the threat is greater today because of a surge in angular towers built from materials like glass and steel that actually promote more ice growth. The acceleration of climate change may also contribute to icing issues.

Last week, ice dislodged from a tower in Midtown and struck a 55-year-old man in the face. On Sunday, the police closed three blocks of Central Park South as ice fell from towers and crashed to the ground.

[Add falling ice from glass towers to a New Yorker’s list of worries.]

A climate for falling ice

While ice and snow may melt upon contact with a warm sidewalk or street, they adhere to the cold nooks and crannies of a building. It’s also easier for ice to form on energy-efficient buildings because they retain heat that otherwise could melt ice.

Then, when the sun appears, the surface below the ice heats up, allowing the ice to release. Now the ice is plummeting down, onto something, or someone, below.

Frank Moscatelli, a clinical professor of physics at New York University, said that falling ice could reach its maximum speed, between 60 and 70 miles per hour, from the top of a 15-floor building.

It would travel the same speed at that height as it would if it fell from the tip of the city’s tallest building, 1 World Trade Center, whose spire climbs to 1,776 feet, Professor Moscatelli said. That’s because of terminal velocity, the maximum speed of a freely falling object.

Clear roofs, trees and gutters

The city’s Department of Buildings alerts building owners, construction companies and landlords when the weather is conducive for snow or ice to melt and fall. In fact, city law requires property owners to clear snow and ice to prevent accidents.

They must clear roofs and overhangs, as well as remove ice and snow from trees and gutters.

“Building owners have a legal responsibility to keep their properties safe for the public, which includes taking steps to prevent ice and snow on their properties from posing a falling hazard,” the department said in a statement.

Want more news? Check out our full coverage.

The Mini Crossword: Here is today’s puzzle.

What we’re reading

In an interview, Rudy Giuliani said he was more Jewish than George Soros and used explicit language to describe prosecutors in the United States Attorney’s Office for the Southern District of New York. [New York magazine]

After 32 years, Kevin O’Hara, a mail carrier in Syracuse, is retiring. [Syracuse.com]

For only the second time in his 47-year career, Assemblyman Joseph Lentol of North Brooklyn may face a Democratic primary opponent. [The City]

Coming up today

Decorate cookies and make snow globes at the Museum of the City of New York in Manhattan. 11 a.m. [Free with museum admission]

“The Muppet Christmas Carol” screens at the Metrograph in Manhattan. 4:30 p.m. [$15]

Celebrate the lighting of the largest menorah in Brooklyn, with live music and latkes, at Grand Army Plaza. 6 p.m. [Free]

— Melissa Guerrero

Events are subject to change, so double-check before heading out. For more events, see the going-out guides from The Times’s culture pages.

And finally: From the archives

Even Santa needs a pick-me-up.

Mr. Claus ventured into a Chock Full o’Nuts coffee shop at Fifth Avenue and 35th Street in Manhattan on Dec. 20, 1975, for a cup of joe to keep his Christmas spirit going. After being captured by the Times photographer Paul Hosefros, Santa must have gotten back to work: After all, he had only a few days left to make his list, check it twice and churn out enough goodies for those who made the “nice” cut.

See more old photos at our archival storytelling project, Past Tense, and on Instagram @nytarchives.

It’s Tuesday — be nice.

Metropolitan Diary: Overheard in Midtown

Dear Diary:

A woman on her phone is giving directions to someone on the other end of the call.

“I’m on 57th Street, between Fifth and Madison.”

Pause.

“The Chanel side.”

— Nancy Turner

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