AAABoulder, Colorado (CNN) -- Colorado residents are keeping a wary eye on the sky as more rain is forecast for Sunday. As dawn broke, officials worried about continued rescue operations.
"We're going to be in for some steady rain over the next 12 hours," said Kim Kobel, a spokesperson for Boulder's Office of Emergency Management. It shouldn't total more than 1 to 2 inches though. "So that's the good news," Kobel said.
Still, authorities worry that any additional water on ground that's already soaked by up to 15 inches of rain will cause more flooding and dislodge mud and debris. Also, the omnipresent clouds pose a problem for aerial rescue efforts. "It's unlikely at this point that we'll be able to reach those who are stranded in the hard-to-reach areas," Kobel said.
Hundreds unaccounted for
At least four deaths have been blamed on the flooding, and a fifth person is presumed dead. More than 500 were unaccounted for, although authorities cautioned that designation included people who simply have not yet contacted concerned relatives elsewhere.
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Elected officials were looking past the crisis to plan the recovery.
Gov. John Hickenlooper said he spoke by phone with U.S. Transportation Secretary Anthony Foxx, who "was adamant that the $5 million that was released Friday was just the beginning" of federal assistance.
"We're going to come back and rebuild better than it was before," the governor said.
Hickenlooper said experts from Vermont will arrive next week to share lessons about improved road-building learned in the wake of Hurricane Irene.
Damage worth millions
Boulder County alone will need an estimated $150 million to repair 100 to 150 miles of roadway and 20 to 30 bridges, county transportation director George Gerstle said. The repair bill will be "10 to 15 times our annual budget," he said.
A helicopter surveillance mission Saturday carrying Hickenlooper and members of Colorado's congressional delegation was diverted twice to pick up people waving to be rescued.
After the officials' delayed arrival at a Boulder airport, U.S. Sen. Mark Udall promised a bipartisan push in Congress for federal aid for flood recovery. "That dog and the cat and those seven people on those two helicopters didn't ask us whether we were Democrats or Republicans," Udall said.
President Barack Obama signed a major disaster declaration for Colorado on Sunday and ordered federal aid to supplement state and local recovery efforts in Boulder County.
Some storms appeared Saturday slightly east of the most flood-damaged areas, pounding southeast Denver with 1.73 inches of rain in less than 30 minutes.
But skies were clear for much of the day elsewhere, allowing rescues and a more complete count of those not yet located.
The Larimer County sheriff's office said that about 350 people were unaccounted for in the county. That number jumped sharply Saturday afternoon as rescuers reached more empty homes, even though authorities believe those residents got to safety.
In neighboring Boulder County, 231 people were on the "unaccounted for" list as of 7 p.m., said Gabrielle Boerkircher, spokeswoman for the county Office of Emergency Management. She said that number was fluctuating as some people were found safe even as the county received new requests to locate people.
Death toll may rise
Boulder County Sheriff Joe Pelle said authorities have to be "realistic" about the chances that the death toll will rise as rescuers penetrate farther into isolated areas.
No new deaths were confirmed Saturday, but Larimer County officials said a 60-year-old woman was presumed dead after witnesses saw her being swept away by floodwaters that demolished her home. Neighbors tried unsuccessfully to rescue the woman, said Nick Christensen, executive officer of the sheriff's office. Her body had not been recovered.
Teens swept away
The four confirmed deaths included a man and a woman, both 19, who were swept away after leaving their car Thursday in Boulder County. Authorities said the woman left the car first, and the man jumped out to try to save her. Authorities recovered both bodies.
Another body was found in a collapsed home in Jamestown in the same county. Rescuers recovered another body on a roadway in Colorado Springs in El Paso County.