The National Weather Service says it believes North Dakota's Red River crested Saturday at lower-than-predicted levels and a day earlier than expected, as residents of Fargo and nearby towns were bracing for devastating flooding.

Forecasts Saturday showed the river would rise to its highest level of 42 feet on Sunday.

But later Saturday, weather authorities in the region gave Fargo residents a dose of good news, saying the flood outlook for the Red River seemed to be improving and may not be as dire as originally expected.

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Mike Hudson of the weather service said the Red River may already have crested around midnight at 40.82 feet. As of 5:15 p.m., it had dropped to 40.53 feet, a significant shift from earlier forecasts that predicted the river would crest as high as 43 feet -- the same level as the dikes protecting Fargo.

But the river might still rise and recede by a foot either way, given that ice floes affect its flow and could lead to periodic increases.

"River levels may fluctuate over the next several days," said the NWS of Eastern North Dakota/Grand Forks. "The river is currently above record levels and at this time, the level is expected to very slowly decrease over the next several days."

Fargo officials said their analysis concluded the river hadn't yet crested and was on track to hit its high point Sunday.

"The river is still expected to crest tomorrow at 42 feet, even though the level has gone down slightly today," City of Fargo Police Sgt. Ross Renner told FOXNews.com, citing what was reported at an 8 a.m. Saturday briefing.

Melting snow will likely cause water levels to swell again in the coming days, and flood warnings continued for the region, according to weather officials and police.

The snow run-off "will more than likely raise the levels again," Renner said.

Earlier Saturday, the rising of the river slowed because of bitterly cold temperatures, buying time before potentially massive floods slammed Fargo and nearby towns.

The improved situation is a result of the frigid weather: Cold temperatures froze the water that would have flowed into the river, halting its rise, said Hudson. By the time that water thaws, the biggest flooding threat should have passed, he said.

Forecasters acknowledged that the situation could still take a turn for the worse, with a storm predicted to strike early next week with more snow and strong wind.

Fargo Mayor Dennis Walaker encouraged optimism — mixed with caution.

"The best news we can take from this is the river has crested," Fargo Mayor Dennis Walaker said. "But diligence is going to have to be required for at least eight more days and hopefully things will continue to drop.

"The only thing that would change all that optimism would be to have a significant storm that could change that. I'm optimistic."

The situation continues to be a waiting game for volunteers who have spent days shoring up dikes and levees to try to prevent widespread flooding destruction across the city.

Local officials sounded themes of war as they called on residents to stay strong.

"Now it's time to stand and defend," said Tim Mahoney, a Fargo city commissioner.

As the day wore on, North Dakota officials intensified their efforts to fend off the floodwater of the Red River, deploying high-tech Predator drone aircraft, calling up more National Guard troops and asking residents to be on the lookout for any breaches in levees.

Millions of sandbags were in place Saturday. Officials said they were increasing the number of guard troops from 1,700 to 1,850 and bringing in 300 large bags that hold a ton of sand and could be dropped by helicopter into breaks in the levees.

Predator drones from the Grand Forks Air Force Base began flying overhead Saturday morning, providing officials bird's-eye views of the situation and allowing them to react quickly if flooding worsens.

"They will be up there for 10 hours today providing video of the flood situation," North Dakota Gov. John Hoeven said in an interview with The Associated Press.

No major levee breaches or other issues were reported during the night.

Earlier Saturday, the National Weather Service predicted the Red River would crest at near 42 feet sometime Sunday, but said it was still possible the river could rise to 43 feet.

That's as high as the levees go and is nearly 3 feet above than the 1897 record.

President Barack Obama assured the nation Saturday he was keeping close watch on the Midwest floods and putting the government's full weight behind efforts to prevent disaster.

"Even as we face an economic crisis which demands our constant focus, forces of nature can also intervene in ways that create other crises to which we must respond — and respond urgently," the president said in his weekly radio and Internet address.

"I will continue to monitor the situation carefully," he pledged. "We will do what must be done to help."

The Red River was at 40.82 feet Saturday morning, and for the next week it could be bouncing within a couple of inches of 41 feet, meaning the agonizing wait will continue for several days in the Fargo area.

Even after the river crests, the water may not begin receding before Wednesday, keeping up the pressure threatening levees put together mostly by volunteers.

"There are a lot of variables in this whole process, a lot variables," said Fargo Mayor Dennis Walaker. He said there was not enough time to build the levees any higher than 43 feet.

While the situation in Fargo was getting the most attention, officials across the river in Moorhead, Minn., were also dealing with the threat of heavy flooding.

Thousands of people had evacuated that city of 30,000, although others stayed behind.

"Now we’re just collectively holding our breath," Moorhead Mayor Mark Voxland told FOX News on Saturday.

He said he has faith in the levees residents have built, but the full effects of the flooding wouldn't be known for seven days.

"The dikes are very solid. They’re built the right way: twice as wide as they are high," Voxland said. "It’s just going to be how the river reacts to these levees."

Added Clay County, Minn., Sheriff Bill Bergquist: "Right now we're confident, but if the dikes break we'll have people standing on their roofs."

Temperatures were in the single digits during the night, preventing snow from melting and feeding the rising river. The Red rose less than a foot Friday, compared to 2.5 feet on Thursday.

Officials of Fargo, a city of 92,000 people, said Saturday they didn't immediately need any more volunteers.

Volunteers had piled sandbags on top of miles of snow-covered dikes, with the frigid weather freezing the bags solid as they worked.

Hundreds more Guard troops poured in from around the state and neighboring South Dakota, along with scores of American Red Cross workers from as far away as Modesto, Calif. Homeowners, students and small armies of other volunteers filled sandbags.

Missouri Gov. Jay Nixon said Saturday his state's National Guard was sending two C-130 aircraft with at least 34 troops to help.

"It's to the point now where I think we've done everything we can," said Fargo resident Dave Davis, whose neighborhood was filled with backhoes and tractors building an earthen levee. "The only thing now is divine intervention."

Federal officials we prepared to shelter and feed 30,000 people for a week, said Homeland Security Secretary Janet Napolitano.

More people than that may be evacuated, but she said officials expect most people would seek help through friends and family first. She said the Coast Guard had participated in 82 rescues by Friday.

In a flooded small community north of Fargo and across the river, fire destroyed a house surrounded by so much water that firefighters couldn't get within 200 feet. More than 100 residents of Oakport Township, Minn., had to be rescued by boat.

Fargo escaped devastation from flooding in 1997, when Grand Forks was ravaged by a historic flood 70 miles to the north.

This year, the river has been swollen by heavier-than-average winter snow, combined with an early freeze last fall that locked a lot of moisture into the soil. The threat has been made worse by spring rain.

"I think the river is mad that she lost the last time," said engineer Mike Buerkley, managing a smile through his dark stubble as he tossed sandbags onto his pickup truck after working 29 straight hours.

National Guard member Shawna Cale, 25, worked through the night on a dike, handing up sandbags that were 30 to 40 pounds and frozen solid.

"It's like throwing a frozen turkey," said sister-in-law Tawny Cale, who came with her husband to help with the sandbags and then to help Shawna move her valuables as she evacuated.

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FOX News' Alicia Acuna, FOXNews.com's Catherine Donaldson-Evans and The Associated Press contributed to this report.