FORT COLLINS - A late-night surge of water on the Poudre River has prompted the closure of city bridges that cross the river in Fort Collins.

City officials said they would be closing the bridges after flooding became more severe after 11 p.m. Thursday.

Emergency responders using radio communications indicated the river could begin to see flows of 10,000 cubic feet per second after water began topping over Seaman Reservoir in the Poudre Canyon.

Bridges along the Poudre will be closed at Overland Trail, Taft Hill Road, Shields Street, College Avenue, Linden Street, Lincoln Avenue, Mulberry Road, Lemay Avenue, Timberline Road, Prospect Road and Harmony Road west of I-25.

By 9 p.m., the Poudre River had surpassed flood stage at the mouth of the Poudre Canyon, according to readings from the city of Fort Collins' stream gauges.

In Weld County, mandatory evacuations were ordered Thursday night for the River Valley and Idaho Creek subdivisions in Johnstown.

Earlier Thursday, the Larimer County Sheriff's Office warned Poudre Canyon residents to evacuate or be prepared to move to high ground after the Poudre River surged to near flood-stage levels. The sheriff's office sent 408 emergency notifications to Poudre Canyon residents living in low-lying areas near the river.

An American Red Cross emergency shelter has been set up for canyon evacuees at Timberline Church, 2908 S. Timberline Road, in Fort Collins.

An additional 80 notifications were sent to residents living along Buckhorn Road between Bear's Lair and Masonville.

The forecast peak of 10.6 feet would set a record. City officials advise people to avoid low-lying areas around the Poudre River, as an expected peak flow of 7,000 cubic feet per second is close to the all-time peak flow set in April 1999. That's the equivalent of 52,360 gallons of water passing by a point each second.

Areas in Fort Collins along the Poudre River city crews are closely monitoring include the east side of College Avenue, Mulberry Street east of Lemay Avenue, the area around East Prospect Road and Sharp Point Drive, West Harmony Road west of I-25 and all bridge crossings.

No evacuations have been ordered within the city and the flooding hasn't impacted city drinking water, according to a release.

Two people were killed in Boulder County, where up to 6 inches of rain fell in 12 hours overnight Wednesday and Thursday morning. Another person was killed near Colorado Springs.

Hillsides damaged by the High Park, Waldo Canyon and Four Mile wildfires let loose debris as water from the heavy rains washed down into the Front Range. From Colorado Highway 14 in the Front Range's northern reaches in the Poudre Canyon, to points south of Colorado Springs, mountain residents were trapped by roads covered by water or clogged with debris.

State highways across Northern Colorado sustained extensive damage. Colorado 14 collapsed in at least two places in the Poudre Canyon, according the Colorado Department of Transportation. U.S. 34 collapsed in at least two places, while Colorado 7 and U.S. 36 were also damaged, cutting off the Front Range's prime routes to Estes Park and Rocky Mountain National Park.

Shortly after 9:30 a.m. Thursday, county emergency officials said a portion of U.S. 34 in the Big Thompson Canyon near Drake collapsed due to flooding. Shortly after, emergency officials issued a mandatory evacuation order for the Big Thompson Canyon west of Loveland due to the risk of rising water.

Those west of mile marker 74 were advised to head to Estes Park, while those east were asked to evacuate to Loveland. Those stuck in the Drake area were advised to stay in their home but have a plan to quickly reach higher ground.

"This thing continues to rise," Larimer County Sheriff Justin Smith said of the engorged Big Thompson River. Smith called the response to widespread flooding a "72-hour operation" that will keep his deputies running into the weekend.

South of the Big Thompson, a family of thee and a dog remain stranded but uninjured atop their home along Larimer County Road 47 between Estes Park and Lyons after the road washed out Wednesday night.

Would-be rescuers in vehicles and helicopters have been turned back by the fast-flowing water and steady rain across the county, Smith said. Deputies are still unable to get into flood areas, while others are stuck in their current location, walled-in by water.

More than 1,000 evacuation calls have been sent to the Big Thompson and Big Elk Meadows areas Thursday morning, Smith said. Sheriff's deputies have asked people to avoid both U.S. Highways 34 and 36, as sightseers are blocking the roadways.

By 2 p.m. Thursday, about 20 people had come to the Loveland evacuation shelther at the Thompson Valley Schools Administration Building, 1800 S. Taft Ave. People brought pets, used the phone to check in with loved ones and grabbed some food while American Red Cross workers strived to gather towels so evacuees could shower.

Virtually all mountain roads west of Fort Collins are closed in some form, including Colorado 14, Rist Canyon, Stove Prairie, Buckhorn, Redstone Canyon and County Road 23. Rocky Mountain National Park remains open, but virtually inaccessible from the Front Range due to flood-related road closures.

Stove Prairie Elementary School is closed Thursday due to the closure of Stove Prairie Road, according to Poudre School District. Other PSD schools are operating regularly.

The county has no estimated time for re-opening the roads, as officials are assessing much of the damage they couldn't see at night and unable to access some areas. Larimer County has opened its Emergency Information Center for public calls at (970) 498-5500.

Smith said before the 12:30 p.m. news conference in Loveland that flooding is happening along Stove Prairie and to the bottom of Poudre Canyon, with water closing in on homes in Poudre Park.

He said flooding began last night in Poudre Canyon, with storms hitting Estes Park later on. One sheriff's deputy was trapped by water in the Big Elk Meadows area but was safe, he said.

A flood warning remains in effect for much of Northern Colorado through 8:30 p.m. Thursday, while a flash flood warning for southwestern Larimer County is in effect through 9:30 p.m. A warning indicates that potentially life-threatening flooding could occur.

As of 1:30 p.m., nearly 6 inches of rain have fallen on Rist Canyon in the past 24 hours, according to U.S. Geological Survey rain gauges. About 4 inches of rain have fallen at Glacier View Meadows near Livermore.

Across Fort Collins, between 2-3 inches of rain fell. As rain continues, anyone who notices drainage problems in Fort Collins is encouraged to call the city at (970) 221-6700.

Nearly 900 customers of Poudre Valley REA were without electricity at 1:50 p.m. Thursday. Most lived in the Lyons area, but some outages were reported in the mountains west of Fort Collins.

Weld County remains under a NWS flood warning until 8:30 p.m. Thursday. Those who want to report high water, washouts and other road hazards should call (970) 304-6522. The Town of Windsor has not reported any flood-related problems or road closures.