Numerous school systems across metro Atlanta and north Georgia have canceled classes for Tuesday in anticipation of the coldest weather in nearly two decades.

Officials in the cities of Atlanta, Decatur and Marietta as well as in Barrow, Clayton, Cherokee, Cobb, Coweta, DeKalb, Douglas, Fayette, Forsyth, Fulton, Gwinnett, Henry, Lumpkin, Newton, Paulding, Pickens, Troup and Walton counties announced Monday that schools would be closed Tuesday, when morning temperatures are expected to plunge as low as 6 degrees with sub-zero wind chills.

“We do not want students standing at bus stops when the temperature is six or seven degrees and the wind chill is below zero,” said Jay Dillon, the spokesman for the Cobb County School District. “If a bus were to fail to start, the students on that route could be stranded at the bus stop for a long time. The prospect is too risky in such extreme cold.”

Fulton County schools spokeswoman Susan Hale said this is the first time in at least a dozen years the system has closed schools due to abnormally low temperatures.

The system’s fleet of school buses haven’t run for nearly two weeks while students were out for Christmas holiday break. And there’s a possibility the buses may have problems starting up and running properly in the severely cold weather, Hale said.

Besides that issue, the school system does not want children waiting for school buses in the frigid temperatures, she added.

“We want to make sure students are safe from the cold,” Hale said.

Thomas Algarin, a spokesman for the Marietta schools system, said education officials there also decided to call off school for similar reasons as Fulton.

“The temperatures are expected to be abnormally low, so that is affecting diesel vehicles,” he said. “Ninety percent of our (bus) fleet is diesel.”

Diesel changes its form in cold weather.

“It becomes more like a gel than liquid,” Algarin said.

Temperatures dropped through the freezing point into the low to mid-20s across metro Atlanta Monday morning, but the overnight precipitation had mostly ended by 5 a.m., and no widespread icing was reported on metro roadways.

The temperature had dropped from the low 50s at midnight to the low to mid-20s by daybreak. Readings at 9 a.m. included 21 in Dunwoody, 22 in Alpharetta, Chamblee and Dallas, 23 in Marietta and Cartersville and 25 at Hartsfield-Jackson International Airport.

Northwest winds gusting to nearly 40 mph dropped the wind chill to as low as 7 degrees.

In the mountains, the mercury had dropped to 16 in Blue Ridge by 8 a.m.

The state Department of Transportation reported at 6:15 a.m. that road crews had been treating isolated icy patches on state routes in Dade, Murray, Walker, Whitfield, Fannin, Gilmer, Pickens, Floyd and Hall counties.

Later in the morning, as temperatures continued to drop, isolated icing problems surfaced in metro Atlanta.

Just before 6:30 a.m., the Forsyth County Sheriff’s Office tweeted that deputies were reporting black ice on Ronald Reagan Blvd near Peachtree Pkwy. Cobb County authorities reported before 7 a.m. that patches of ice had developed on Kennesaw Due West Road near Frank Kirk Road, at the intersection of Barrett Parkway and U.S. 41 and on Ga. 5 at U.S. 41.

Other icing was reported before 7 a.m. on the Howell Mill Road bridge over I-75 and on I-85 southbound north of Pleasant Hill Road in Gwinnett County, while in Clayton County, the ramp from Forest Parkway to I-75 southbound was blocked after a tree fell onto a vehicle, according to the DOT.

In DeKalb County, the DOT reported an icy patch just after 8 a.m. in the right lane of I-285 eastbound at Chamblee Tucker Road.

The DOT was still receiving scattered ice reports at 9 a.m., including one of an icy patch on Ga. 400 northbound near Martin Road.

North of Atlanta in Bartow County, a truck reportedly wrecked on ice on the I-75 northbound bridge over Lake Allatoona and was hanging off the bridge, according to the AM750 and 95.5FM News/Talk WSB Traffic Center.

In Cherokee County, authorities reported icing on I-575 between exits 11 and 14 as well as on several surface streets.

The bone-chilling cold front sweeping across the mountain counties brought occasional sleet, blustery winds and school closings to the region. A light dusting of snow was on the ground in Blue Ridge.

The threat of dangerous weather conditions prompted public school closings and delays throughout north Georgia. Cherokee, Murray and White counties were among the school systems that closed on Monday.

By 6:15 a.m. Monday — before her 3-year-old wakes up — Atlanta parenting blogger Joyce Brewer had made it to the Starbucks on North Druid Hills Road to begin writing for the day. She was amused by the threat of bad weather.

“I was expecting a horrible ice filled trip to Starbucks this morning where I come to blog about parenting,” Brewer said. “But it was smooth sailing. The first thing I thought was there’s no reason school should be canceled when it doesn’t feel like freezing weather. I’m speaking as a girl from Long Island NY who walked to junior high in six inches of snow.”

Elise Johnson commutes from Warner Robins to the Silver Skillet restaurant near midtown.

“I was on the road at 0-dark-30, but it was a normal commute for me,” she said. “I was expecting to be in before it all hit anyway.”

In metro Atlanta, the worst icing early on was on Roswell Road near Northridge Road, where the northbound lanes were icing over because of a nearby broken water main.

But DOT crews were ready for whatever Mother Nature threw at them Monday morning.

“We had crews come in last night at 10 o’clock and they’ve been working the overnight hours, pre-treating the bridges and making sure all the equipment is ready to go just in case we need it,” DOT spokesman Mark McKinnon told The Atlanta Journal-Constitution.

“We’re really not expecting any snowfall, but we are noticing that temperatures will be dropping and that could cause some icing on the roads, so we’re a little concerned about that,” he said. “We’re hoping that the wind will dry it out before it actually has time to freeze, but there will be some patches of ice and motorists should take heed, drive carefully and if they see any ice, please call 511 and report it.”

By 7 a.m., a group of eight city of Marietta street crew workers had gathered at the Marietta Diner for breakfast - or as one said, dinner.

The crew had been on standby since midnight mixing sand and preparing for icy roads that never came.

“Nothing is going to happen,” said Donnie Lyle. “We been up all night and we are ready, but we think this is about it.”

Spiro Lourentzatos, the diner’s manager, said the morning crowd was typical.

“The weather has had no impact at all. This is a normal day,” he said. “I from New York. I am use to this. I just hope people drive safe.”

Before walking into the diner, Acworth resident Ray Gary stopped to get a paper out of the box. An older regular in the diner shuddered because he left the door open too long.

“The only thing is the cold makes me very uncomfortable. I have to wear more clothes,” said Gary, who was wearing a blazer and sweater. “I am not a spring chicken anymore.”

An hour north of Marietta, the snow was falling heavily in East Ellijay around 7 a.m. as Art Dawe ate fried eggs and hash browns at the Waffle House just off Highway 515. The fishing guide had driven in from Copperhill, Tenn., chaperoning a relative here for a job interview. Dawe said he drove his Dodge pickup cautiously.

“No need to be in a hurry on a day like today,” he said.

A police officer sitting next to Dawe chuckled as he spotted motorists rolling through a nearby stop sign. He guessed they didn’t want to hit their brakes out of fear that they would spin out.

Moments earlier, Tucker Plouffe was trudging through the snow to start bagging groceries at the Ingles grocery store across the street. He had just arrived from Whitepath. He said he drove “slow and in a low gear,” slipping only once on his way to work. Standing nearby in the parking lot, his coworkers shrugged at the thin layer of snow on the ground, saying they had seen worse in North Georgia and in other states.

“I’m from Michigan, so this isn’t anything,” one said.

Atlanta firefighters battled the elements as well as the flames to douse a blaze that broke out just before daybreak Monday in an abandoned house on Center Hill Avenue near Donald Lee Hollowell Parkway in northwest Atlanta.

The house was almost 100 percent consumed by flames when firefighters arrived, Atlanta fire Battalion Chief Stephen Hill said.

“Flames were already through the attic, and we could see them up in the sky on our ride over here,” Hill said.

He told The Atlanta Journal-Constitution that the subfreezing temperatures make firefighting particularly dangerous.

“With the runoff from the hoses, we have ice build-up. Ice builds up on their turnout gear and equipment,” Hill said.

“In conditions like this, we have to swap [firefighters] out and give them the ability to get water and Gatorade,” he said.

“A lot of times, MARTA will bring a bus and we will go rehab on the bus in extreme temperatures, hot or cold,” Hill said. “It’s just as important in cold weather as it is in hot weather to stay hydrated.”

Hill said there’s usually a spike in fires during extremely cold weather because “people are trying to stay warm and they will go to extreme measures to stay warm using more space heaters, using more unconventional methods of heating, and sometimes those will end up catching structures on fire.”

With no major metro icing issues, the concern Monday was turning to the bitter, Arctic cold expected to rush into the state by early Tuesday.

Channel 2 meteorologist Karen Minton said temperatures would remain in the 20s Monday afternoon before plummeting to around 6 degrees before sunrise Tuesday. That would be the coldest temperature in metro Atlanta in nearly two decades, and would shatter the old record low for the date of 12 set in 1970.

Wind chills will be well below zero metro-wide Monday night, forecasters warned.

Tuesday will be continued cold and windy, with highs only climbing to around 24 degrees before dropping back into the mid-teens Tuesday night, Minton said.

The rest of the week will be a little warmer, with highs in the low 40s Wednesday and Thursday and around 50 degrees Friday. Late-week lows will warm into the mid-30s.

Staff photographer John Spink and reporters Jeremy Redmon, Rose French, Ernie Suggs, Michelle Shaw, Andria Simmons, Ty Tagami and Tammy Joyner contributed to this article.