Updated 4:36 p.m. ET
MOORE, Okla. With her son holding her elbow, Colleen Arvin walked up her driveway to what was left of her house of 40 years.
It was the 83-year-old grandmother's first time back at her home since a monstrous and deadly tornado ravaged her neighborhood in suburban Oklahoma City. Part of the roof was sitting in the front yard, and the siding from the front of the house was gone. As her son, Jeff, and her grandsons picked through what was left of her belongings, Arvin found some dark humor in the situation.
"Oh thank God," she said, laughing, when a grandson brought over her keys. "We can get in the house."
Monday's tornado killed at least 24 people and destroyed thousands of homes. Officials said Wednesday six adults remain missing, but it is unclear whether or not they simply haven't made contact with relatives and friends yet. The storm also reduced one elementary school almost entirely to rubble, killing seven children inside. In all, the twister is known to have taken the lives of 10 children, including two infants.
Courtney Brown, 8, one of the many children who took refuge at Plaza Towers Elementary School in Moore, told CBS News she saw the tornado rip away the roof. She survived, but seven others at the school did not.
The school was "turned into crumbles," Brown said.
More than 320 people were treated by local hospitals, according to a CBS News survey.
The tornado has now been officially classified as an EF5 -- the highest, most violent rating. Scientists say the tornado had the power of many atomic bombs.
Oklahoma City Mayor Mick Cornett told CBS News correspondent Jeff Glor he's amazed anyone's around to remember it.
"No one could possibly have survived this, and yet we know they did," Cornett said. "We know people crawled out of the rubble. This was the storm of storms."
Moore Police spokesman Jeremy Lewis said more than 200 people were rescued from the rubble -- all of them Monday night. No survivors were found Tuesday, he added.
Moore Fire Chief Gary Bird said Tuesday he was confident there are no more bodies or survivors in the rubble. Every damaged home had been searched at least once, Bird said, but his goal was to conduct three searches of each building just to be certain there were no more bodies or survivors.
"I'm 98 percent sure we're good," Bird said.
CBS Oklahoma City affiliate KWTV reports some of the 122 National Guard members deployed in the area were using thermal imaging technology as they scoured the rubble, looking for anyone still trapped and for any remaining bodies.
There have been conflicting reports about the number of homes damaged or destroyed. Moore police spokesman Lewis said about a quarter of the homes in Moore were damaged or destroyed, which would would amount to 4,000 to 5,000 houses. Oklahoma City Mayor Cornett said 12,000 to 13,000 homes were affected.
The cost of the tornado could be more than $2 billion, according to a preliminary estimate announced Wednesday by the Oklahoma Insurance Department.
Spokeswoman Calley Herth told The Associated Press that the early tally is based on visual assessments of the extensive damage zone stretching more than 17 miles and the fact that the tornado was on the ground for 40 minutes.
Federal, state and local officials have assured residents there will be ample funds for recovery. President Obama has promised "full focus" on the effort, while Okla. Sen. Tom Coburn said that as the top Republican on the Homeland Security and Governmental Affairs Committee, which oversees the Federal Emergency Management Agency (FEMA), "I can assure Oklahomans that any and all available aid will be delivered without delay."
President Obama plans to meet with victims and first responders, and view the destruction firsthand when he visits the area on Sunday, White House spokesman Jay Carney said.
Some 34,000 Oklahomans were without power Tuesday, including 14,000, in Moore, according to the Oklahoma Corporation Commission and State Office of Emergency Management.
Secretary of Homeland Security Janet Napolitano said FEMA has already begun helping expedite the removal of debris, and will soon begin assisting in the distribution of bulk goods like tarps, gloves and mops to aid in the recovery phase of the disaster.
As state and federal officials work to set up disaster recovery centers to provide aid and assistance, Arvin and other residents of Moore are beginning the deliberate process of assessing what's left of their homes and possessions and what comes next.
Officials are still trying to make sense of what will be needed in the coming days, weeks and months: Will homes be rebuilt or torn down? Where will the children go to school? How much will it all cost?
Officials were not certain of how many families had been displaced. Emergency crews had trouble navigating devastated neighborhoods because there were no street signs left. Some rescuers used smart phones or GPS devices to guide them through areas with no recognizable landmarks.
The Arvins and others looked for bright spots throughout an otherwise dark day. Arvin's son Jeff noticed a set of five dishes without a single crack. He and his nephews pulled out golf clubs, pictures and a decorative key and note holder.
It was an ordeal they've faced before.
Monday's tornado, which traveled 17 miles and was 1.3 miles wide at points, loosely followed the path of a twister that brought 300 mph winds in May 1999.
The National Weather Service said the latest tornado, which was on the ground for 40 minutes, was a top-of-the-scale EF5 twister with winds of at least 200 mph -- the first EF5 tornado of 2013.
This week's tornado was the fourth since 1998 to hit Moore, a middle-class community that has been one of the fastest-growing suburbs of Oklahoma City.
"'99 taught us a lot, especially in Moore -- such as, you've got to have a plan," Jeff Arvin said.
Billy McElrath's entire home was reduced to rubble, and even its concrete foundation was split. His wife and a friend McElrath hired to do some painting managed to make it into an underground shelter moments before the tornado shredded the home.
His 1968 red convertible Corvette was smashed under heaps of bricks and wooden frames inside what was left of his garage.
"My wife got it for my 50th birthday last August," McElrath said. "I haven't driven it since my son and I took it to a car show in Springfield last September."
His plan was simple: "We'll just start over."
Survivors emerged with harrowing accounts of the storm's wrath, which many endured as they shielded loved ones in hallways, closets and bathrooms.
Larry Harjo, his twin brother and their wives headed for the hospital at the end of the street only minutes ahead of the tornado that ripped the roof off their home and blew out its walls.
"We could see the tornado coming. We could see one side of it, but we couldn't see the other so we knew it was big," Harjo, 45, said while standing in his driveway. "There was no surviving that. It was either underground or out of the way kind of thing -- and we got the hell out of Dodge."
The hospital was their plan. They had sheltered there before, but this time, it took a direct hit.
"We were directly center of the hospital and we could hear the cars hitting the building, so we knew it wasn't going to be nice," he said. "Thump, thump, thump. Loud thumps."
"Ceiling tiles falling everywhere. I thought it was going to cave on us there for a minute," he said.
From the air, large stretches Moore could be seen where every home had been cut to pieces. Some homes were sucked off their concrete slabs. A pond was filled with piles of wood and an overturned trailer. Also visible were large patches of red earth where the tornado scoured the land down to the soil. Some tree trunks were still standing, but the winds ripped away their leaves.
Officials had revised the death toll downward from 51 to 24 on Tuesday after the state medical examiner said some victims may have been double-counted in the confusion immediately after the storm.