Fifty years after a downpour transformed the Big Thompson Canyon into the site of one of the deadliest natural disasters in Colorado history, the focus of a lineup of speakers in Estes Park was not only on what happened the night of July 31, 1976, but on what has been learned since.

Scientists, historians, emergency managers and flood experts gathered Friday at the Estes Valley Community Center for the Big Thompson Flood 50th Anniversary Symposium, using the anniversary to reflect on a tragedy that claimed 144 lives while reminding residents that the same hazards remain today.

Colorado State Climatologist Russ Schumacher opened the symposium by reminding attendees that while forecasting technology has advanced dramatically over the past five decades, the ingredients that created the catastrophe still exist.

“The Big Thompson storm really maximized the rainfall rate and the duration in this very localized area,” Schumacher said. “That led to the flood disaster.”

Schumacher explained that extreme rainfall depends on two simple factors — how hard it rains and how long it rains in one location. On July 31, 1976, the storm achieved both.

Powerful easterly winds carried unusually moist air up the Front Range while weak upper-level winds kept the thunderstorms nearly stationary over the headwaters of the Big Thompson Canyon. The result was an estimated 11 to 12 inches of rain falling in just a few hours.

Although meteorologists now have Doppler radar, satellites, sophisticated computer models and far more atmospheric observations than were available in 1976, Schumacher said, predicting the exact location of a storm capable of producing catastrophic flooding remains one of meteorology’s greatest challenges.

Flashback to the world in 1976

In her presentation at the symposium, Colorado State University water resources archivist Patty Rettig focused on what the world was like when the the Big Thompson Flood occurred.

In 1976 there were no smartphones, internet, social media, wireless emergency alerts or reverse 911 notifications. Cameras required film, telephones were tethered to walls by wires, and flood insurance was still relatively uncommon.

“There was no 911, and there was no (telephone notification system),” Rettig said. “Only one person in the canyon had flood insurance.”

An estimated 600 people lived in the canyon, she said, but as many as 3,500 visitors were there that Saturday enjoying picnics, camping and recreation.

“There were more tourists in the area,” Rettig said. “People were ready to celebrate. They were relaxing. They were picnicking.“

Drawing from oral histories preserved in CSU’s Water Resources Archive, Rettig described first responders recalling a night so dark they could hear propane tanks hissing as they floated downstream but could barely see the water itself.

Others remembered neighbors refusing to believe the warnings because what was happening seemed impossible.

“They didn’t believe what was happening,” Rettig said. “There was just this feeling of disbelief.”

When daylight arrived, Highway 34 had been ripped apart. Forty-two bridges were destroyed. Entire homes had disappeared from their foundations. The Big Thompson hydroelectric plant at what is now the Historic Fall River Hydroplant site had been demolished. Helicopters spent days rescuing survivors stranded on rocks and in trees.

The statistics remain staggering: A river that normally carries about 165 cubic feet of water per second surged to an estimated 31,000 cubic feet per second. The flood crest rose roughly 19 feet and traveled 8 miles from Glen Comfort to Drake in only 25 minutes.

A tragedy that reshaped emergency management

For Larimer County Director of Emergency Management Lori Hodges, last year’s deadly flooding in the Texas Hill Country was a deeply personal reminder that even half a century after the Big Thompson Flood, the work of protecting lives is never finished.

“I actually went into kind of a deep depression when that flood happened,” Hodges told symposium attendees. “I had kind of my first crisis of faith in emergency management because I felt like, ‘Have we learned nothing?’ “

As she researched the Big Thompson Flood in preparation for the symposium, however, that discouragement gradually turned into optimism.

“What I learned from that is that we did learn a lot,” she said. “I actually came out of that much more hopeful than I was this time last year.”

The reports written after the 1976 disaster did more than document what happened, Hodges said. They became blueprints for change.

“They didn’t just write a report about it and put it on a shelf,” she said. “They took those reports and they made something better. They made a stronger system from it.”

In 1976, radar coverage was limited, rain gauges were sparse, and emergency alerts often depended on first responders driving through the canyon or members of the Larimer County Sheriff’s Posse riding horseback to warn residents as floodwaters rose.

Larimer County has developed new warning protocols following more recent disasters, including an “imminent threat” alert implemented after the 2020 Cameron Peak Fire to warn residents of life-threatening flooding in burn scars.

But the lessons, she said, extend beyond emergency management.

“I think people learned that nature doesn’t negotiate,” Hodges said. “We have to live with nature instead of trying to fight against it.”

Retired Denver7 Meteorologist Mike Nelson gives a presentation at the Big Thompson 50th Anniversary Symposium on Friday at the Estes Valley Community Center. (Jeffrey Bear / Trail-Gazette) Changes in forecasting

Retired Denver7 meteorologist Mike Nelson echoed Hodges’ message in his presentation, noting that flash flooding remains one of Colorado’s greatest weather hazards.

Showing television coverage from Aug. 1, 1976, Nelson reminded attendees how differently weather information was delivered a half-century ago.

“That would have all been on film,” he said. “It would have been edited and sliced together with Scotch tape.”

Since then, weather forecasting and public communication have been transformed.

Nelson pointed to the Community Collaborative Rain, Hail and Snow Network, better known as CoCoRaHS, which was created after the 1997 Fort Collins flood to dramatically increase volunteer rainfall observations across Colorado and around the world.

He also warned that climate change is expected to increase the severity of heavy rainfall events.

“We know that severe flooding will happen again,” Nelson said. “It’s a matter of history and time.”

Nelson encouraged residents not to rely solely on free smartphone weather applications, arguing that receiving warnings through multiple sources improves the chances of taking action in time.

“Layers save lives,” he said.

Communication is key

Jennifer Stark, meteorologist in charge of the National Weather Service office in Boulder, offered a personal perspective in her presentation.

A Colorado native, Stark was a child when the Big Thompson Flood occurred.

“I remember waking up the morning after the flood,” she said. “We were listening to the big console radio and listening to the news because that was a really effective way to understand the magnitude of what was happening.”

The experience left a lasting impression.

“Every summer afternoon after the flood, if it would start to rain, my sister and I would start crying in the back seat of the car, saying, ‘It’s going to flood.’ “

Today, Stark said, the National Weather Service has shifted its focus beyond simply producing forecasts.

“Our focus is on communicating the forecast and the impacts of the weather to the people that are going to be impacted,” she said.

That communication depends on partnerships with emergency managers, broadcasters and local governments to make sure warnings reach people before disaster strikes.

“The last mile is getting the word out to the public,” Stark said. “And then the public taking action.”

She urged residents to ensure wireless emergency alerts remain enabled on their phones and to keep NOAA weather radios in homes and campsites, especially for nighttime storms.

Hydrologist Bob Jarrett, who was one of the U.S. Geological Survey scientists dispatched into the Big Thompson Canyon immediately after the 1976 flood disaster, gives a presentation at the Big Thompson 50th Anniversary Symposium on Friday at the Estes Valley Community Center. (Jeffrey Bear / Trail-Gazette) Nature still sets the rules

Hydrologist Bob Jarrett has spent much of the last 50 years studying the Big Thompson Flood.

As one of the U.S. Geological Survey scientists dispatched into the canyon immediately after the disaster, he helped measure the flood’s peak flow, map the damage and document an event that would shape flood science for decades.

“We were flown in courtesy of the National Guard,” Jarrett recalled. “The USGS was sent out to document the peak discharges around the storm and determine the overall extent of the storm.”

The work, he said, was sobering.

Members of the survey team encountered victims while conducting field measurements, a reminder that the scientific data represented a human tragedy that had claimed 144 lives.

Those early investigations challenged several assumptions that existed in 1976.

One common belief, Jarrett said, was that the Big Thompson Flood was simply a “100-year flood,” implying residents could expect another century before facing a similar disaster.

He said that subsequent research showed the event was far rarer.

Using decades of stream gauge records, rainfall measurements and a technique known as paleoflood hydrology, which studies ancient flood deposits, tree scars and other geologic evidence, Jarrett and fellow researchers concluded the Big Thompson Flood was closer to a 10,000-year event at that location.

Jarrett said that while the exact combination of atmospheric conditions that produced the 1976 storm was extraordinary, the potential for catastrophic flooding remains throughout Colorado’s foothills.

Jarrett encouraged people to pay attention to the natural warning signs that often precede catastrophic flooding, such as darkening skies, persistent lightning, heavy rainfall, rapidly rising water and the unmistakable roar of a flood moving downstream.

“Virtually every large flood I’ve studied,” Jarrett said, “people said, ‘I thought I heard a large locomotive just coming out of control.’”