Colorado floods: Over 500 unaccounted for as 'devastating' rain looms

Boulder, 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.

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.