Evacuations were ordered across Colorado after heavy rain pounded the state throughout Thursday evening and was expected to continue in patches throughout the day Friday. Water levels continued to rise, leading to flooding of "biblical" proportions, according to the National Weather Service.
The deluge extended from the eastern Rockies west to Sterling and reached south toward Colorado Springs. The hardest hit area was in and around Boulder, though flash flood warnings are still in place in central, north central and northeast Colorado.
"There's so much water coming out of the canyon, it has to go somewhere, and unfortunately it's coming into the city," said Ashlee Herring, spokeswoman for the Boulder office of Emergency Management, referring to the Boulder Canyon.
President Obama declared an emergency in Boulder, El Paso, and Larimer counties late Thursday evening that will allow for federal aid, and permit the Federal Emergency Management Agency (FEMA) to coordinate disaster relief efforts.
The Colorado National Guard began evacuating over 4,000 residents along Boulder Creek in Boulder County. The Guard has been using high-clearance trucks to transport residents, according to the Boulder County Sheriff's office.
But the heavy rain has stymied movement.
"We are all pretty much locked in Boulder right now," said Gabrielle Boerkircher, a county spokeswoman. "The main concern is keeping people off the roads. They need to stay safe at home." Regular-sized vehicles can easily be washed away, or tip over in the flood waters.
Over 11 inches of rain had fallen in Boulder from Monday through Thursday evenings, and the city saw more than seven inches of rain in 24 hours, shattering the town's 95-year record for rainfall. The overflow of Boulder Creek, which runs through the city's center, has blocked off thoroughfares in Boulder.
"There's no way out of town. There's no way into town. So, basically, now we're just on an island," Jason Stillman told weather.com. Mr. Stillman and his fiancee were forced to evacuate their home in Lyons at about 3 a.m. Friday after a nearby river began to overflow into the street.
Official reports said that there were mudslides at the mouth of Boulder Canyon due to the saturation from consecutive days of heavy rainfall.
The state's long history of wildfires makes it more susceptible to flooding: scorched earth absorbs water more slowly and holds less, meaning more water from heavy rains is converted into runoff, which converges and produces floods. However, it is unprecedented for Colorado to be hit with such a steady onslaught of rain so late in the year. These "monsoon"-style rains usually occur in late July and August, but are typically brief events that provide the normally dry state with a quick downpour of moisture, reported weather.com.
Seventeen people were unaccounted for early Friday morning, said Boulder County spokesman James Burrrus, with the addendum that "unaccounted for doesn't mean missing.... It means that we haven't heard back from them."
Three reported deaths have been attributed to the flooding. One person was killed by a collapsing house near Jamestown.
A man's body was recovered after a couple were swept away in their car by floodwaters northwest of Boulder. The woman was missing and feared dead, said Commander Heidi Prentup of the Boulder County Sheriff's Office.
The body of a third confirmed fatality, a man, was found by police on flood-watch patrols in Colorado Springs, about 100 miles to the south of Boulder, according to officials.
"It's going to take us a while to rebuild from this, no question," said Colorado Gov. John Hickenlooper Thursday afternoon. "A storm of this size is going to cause severe consequences."