Drop by drop by drop, historic rainfall across a 150-mile expanse of Colorado’s Front Range turned neighborhood streams into rampaging torrents that claimed at least three lives and continued to flood homes and destroy roads into the night.

Heavy rain returned to the region Thursday evening, threatening an equally disastrous Friday.

By the end of Thursday, thousands had been evacuated from their homes in places as far apart as Loveland, Erie and Aurora as rain-swollen creeks and rivers threatened their homes. Nearly every road heading into the foothills of Boulder, Larimer and northern Jefferson counties was blocked by floodwaters or debris. Loveland and Longmont were essentially shorn in two by road closures near the Big Thompson and St. Vrain rivers that kept residents on one side unable to cross to the other.

At least three Colorado towns — Lyons, Estes Park and Jamestown — were entirely isolated by water. Xcel Energy cut off power to most of Lyons. In Estes Park, a community of about 6,000 people, both telephone lines and cellphone towers were down. As darkness fell, the only communication into or out of the town was by ham radio.

“God, it just needs to stop,” said Bob Stahl, who lives within a block of the St. Vrain River in Longmont. “I just hope it quits.”

So fierce and sustained was the deluge that officials said they don’t know how bad the damage is or how long it will take to fix. Roads crews couldn’t reach flooded areas. More heavy rain was expected overnight and Friday morning — both prolonging the rivers’ menace and delaying the recovery from their wrath.

All together, the floods were expected to be some of the worst in state history.

“It’s going to take us a while to rebuild from this, no question,” Gov. John Hickenlooper said Thursday afternoon. “A storm of this size is going to cause severe consequences.”

Even without more rain, flooding was expected to ripple for days.

Flooding is predicted on Friday along the South Platte River east of Greeley, said U.S. Geological Survey spokesman Robert Kimbrough. On Saturday, minor flooding is expected along the same river near Sterling.

“We can anticipate we will see rivers going above flood stages as that flood crest makes its way downstream,” Kimbrough said.

Hickenlooper said he had summoned help from the National Guard. The White House announced Thursday night that President Barack Obama had declared an emergency in Boulder, El Paso and Larimer counties, so that money and resources can come to the state more quickly.

Purely by the numbers, the storm’s might was staggering.

Dozens of communities from Fremont County to Larimer County reported flooding, a swath of rain roughly equivalent to the distance between Baltimore and New York.

For Boulder, which saw some of the worst flooding, Kimbrough said there was only a 1-in-100 chance that a storm of this magnitude would happen in a year — meaning the storm is a proverbial 100-year flood.

Boulder Creek’s flow rate, measured at one point at 4,500 cubic feet per second, was more than twice as large as the previous peak flow recorded during the river gauge’s quarter-century history. Typically the river runs at between 100 and 300 cfs.

With at least 10 inches of rain having fallen across the city since the storm began, Boulder’s 25 square miles were inundated with roughly 4.5 billion gallons of water.

On the University of Colorado at Boulder campus, one quarter of all buildings had suffered some type of water damage, although much of it was minor, a school spokesman said.

Flash-flood warnings lit up Adams, Denver, Larimer, Boulder, Jefferson, Arapahoe, Douglas, El Paso, Lincoln, Cheyenne and Kit Carson counties on Thursday night. The National Weather Service warned that any given storm cell was capable of dropping multi-inch amounts in only a few hours.

“(A) major flooding/flash-flooding event (is) underway at this time with biblical rainfall amounts reported in many areas,” the National Weather Service announced Thursday morning.

State climatologist Nolan Doesken said the floods are not the worst Colorado has ever seen but they are unusual for being so widespread. A stubborn low-pressure system from the north and a persistent suction of moisture from the south have collided over the state, he said. The result is a perpetual loop of rain.

Doesken said the storm is similar to one that occurred in September 1938, when flooding rampaged through Morrison, Eldorado Springs and parts of El Paso County — a storm The Denver Post at the time called “A moment’s madness of the skies.”

“This is not unprecedented,” Doesken said. “It is simply not common.”

The floods’ impact, though still unclear, was devastating.

One man, who neighbors identified as Joey Howlett, 72, was reported killed after a building collapsed in Jamestown, in the mountains above Boulder. Later, the body of a man family identified as Wesley Quinlan was found in north Boulder in the 200 block of Linden Drive. Officials said that man had been with a woman in a car that became stranded in the area. The woman is still missing.

In Colorado Springs, emergency crews checking flooding conditions early Thursday discovered the body of a man in Fountain Creek, near Nevada Avenue and Las Vegas Street. The man was identified Thursday afternoon as Danny Davis, 54.

“The event is far from over,” Boulder County Sheriff Joe Pelle said at a morning news conference. “We know we’ve lost lives. As the day goes on, we may find we’ve lost others.”

Only quick evacuations and moments of heroics prevented other deaths.

Officials in Erie, Longmont and Loveland moved rapidly to evacuate residents in flood-prone areas. Emergency crews in Aurora, Commerce City, Denver and Jefferson County scrambled to rescue drivers stranded in floodwaters.

Firefighters in Broomfield pulled two people out of cars that splashed into floodwaters when the section of Dillon Road that they were driving on crumbled beneath them. A third motorist was able to free himself from his vehicle.

“I have people banging on the doors,” one of the first police officers on scene shouted into his police radio. “There’s one overturned. I’m hearing people banging. I can’t get down there right now.”

North Metro Fire & Rescue firefighters used a raft to rescue the two, who suffered only minor injuries.

Throughout the day, residents in the flood’s path looked on with disbelief as their neighborhoods turned suddenly threatening.

Three Loveland police officers knocked on Julie Demaree’s door at 3 p.m. Thursday to deliver a fairly short, blunt order: “You have 30 minutes, … so get out.”

Demaree and her boyfriend collected their things and their dog and headed toward a hotel near Interstate 25 and U.S. 34. As they left, they looked back on the sliver of the Big Thompson River that runs by Demaree’s condo.

“I liked to walk on the little walking trail there, but now it’s completely flooded,” she said. “By the time we left, the water there had gone up 3 feet.”

Conditions worsened throughout the day in Longmont, and, by late afternoon, the evacuation center at Silver Creek High School had registered 150 people.

“We are having a hard time getting supplies,” said Steve Aubrey, a Boulder County Sheriff’s deputy. “We are checking with the National Guard to see if we can get cots for everyone tonight.”

Many tried to stay upbeat.

On Twitter, a man posted a picture of himself holding a fish he said he caught. The fish was swimming around the basketball hoop in his driveway.

For Grant Hetherington and Jyssica Lasco, the flood washed away their plans to be married Friday at the Stone Mountain Lodge in Lyons. They had spent a year-and-a-half planning the event.

A half-day’s work on Thursday quickly switched the wedding to a venue in Loveland.

“I cried a little, but I’m still marrying my best friend and the love of my life,” said Lasco, 24, “and we’re sending our thoughts out to those affected by the flooding.”

As rain continued to fall into the night, officials said that was about all that could be done. Earlier in the day, Hickenlooper was asked whether the state had the resources to deal with the flooding. The governor insisted it did. It was just that, on Thursday, the rains reigned.

“It’s not that we haven’t had the equipment or the manpower,” Hickenlooper said. “It’s that the conditions haven’t permitted it.”

Staff writers Suzanne Brown, Joey Bunch, Tom McGhee, Jeremy P. Meyer, Kirk Mitchell and Kieran Nicholson contributed to this report.