Cars move through flooded Denver streets after unprecedented rain and hail fell at the intersection of Broadway and and 20th streets on June 15, 1950.
Lowell Georgia, The Denver Post
Hailstorms in Denver in June 1962.
David Mathias, The Denver Post
This is how the 2400 block of S. Marion St. looked at 7:30 a.m. Monday, July 4, 1960, more than 10 hours after a violent hailstorm pounded the area.
Denver Post archive photo
Grant Tyson, 8, son of Denver Post reporter Monk Tyson, gathered a dish of king-size "Sky bullets" from his front yard in Lakewood, 1961.
Ira Gay Sealy, The Denver Post
Hail in Denver June 1968.
Duane Howell, The Denver Post
At 5 A.M. Monday, June 9, 1969 State Highway Department crews were still working to clear Valley Highway. The hauling loader at left broke through piles of hail that reached depth of six feet near South Logan Street.
Duane Howell, The Denver Post
Colorado State Highway Department crews plowed through hail drifts south of the South Logan Street overpass on I-25 on June 9, 1969.
Steve Larson, The Denver Post
Residents of Indian Hills, west of Denver, check a damaged car after a flash flood swept away garages and cars as hail and rain sent the creek surging out of its channel in August 5, 1970.
Barry Staver, The Denver Post
Thunderstorms pound Denver with heavy rain and hail in July 1973.
John Sunderland, The Denver Post
Rain and hail failed to daunt a young bicycle rider in Denver Sunday afternoon, June 6, 1976.
Steve Larson, The Denver Post
A brief hailstorm pelts southeast Denver along County Line Road, just west of Interstate 25 In June 1977.
Bill Peters , The Denver Post
Betty Van Pelt, Douglas County District Court clerk, surveys the shattered windshield of a car, one of many damaged by hail in Castle Rock during a thunderstorm Sunday night, June 20, 1977. The car, which belongs to Rick Rozycki, a dispatcher with Douglas County sheriff's office, was parked out side by when storm hit. Three sheriff's cars were damaged. Bill Peters , The Denver Post
John Sunderland, The Denver Post
An automobile moves through the village of Glen Haven on the North Fork of Big Thompson River during a rainstorm in May 1978. The area west of Loveland was the scene of a tragic flash flood July 31, 1976, and flood worries rose as heavy rain, hail and sleet fell again.
Lyn Alweis, The Denver Post
Snow, fog, and hail are seen on I-70 west of Denver on April 30, 1978.
Rain mixes with snow and hail in the Cherry Creek Shopping Center May 22, 1979. Many intersections became small lakes during downpour.
Karl Gehring, The Denver Post
Vic Chrisman indicated where golf ball sized hail shattered the windshield of his Toyota Camry Saturday, August 4, 1981 in Longmont.
Ed Maker, The Denver Post
Carol Ramb of Wheat Ridge checks a large mound of hail Wednesday morning, June 3, 1981 at 26th Avenue and Quay Street. Hail fell over a wide area overnight,
reaching depths of 6 inches or more in some areas.
Dave Buresh, The Denver Post
Sheridan firemen Ron Packard, left, and Don Ezell shovel hail that was 2 feet deep in spots at the intersection of West Hampden Avenue and South Santa Fe Drive Thursday, June 25, 1982. The avenue was closed to traffic for about two hours because of high water caused by hail-clogged drains.
Dave Buresh, The Denver Post
Looking north on Tennyson from 48th, drivers are unable to get up the hill due to the hail in 1984.
Bill Wunsch, The Denver Post
Ann Brown being evacuated from her mobile home helped by members of Southwest Adams County Fire Department members June 13, 1984. She had a total hip operation just two weeks earlier.
Karl Gehring, The Denver Post
Sam Tanaka watched a storm move over his cabbage patch hit hard with hail. Tanaka has 800 acres of cabbage, all hit by hail in 1986. "This is ruined," he explained, "nobody will buy them. Tanaka and his brothers run vegetable market south of Longmont.
Brian Brainerd, The Denver Post
Bob Stotts, age 15, sought the shelter of a bush along Jewell avenue in Lakewood as an afternoon storm swept across the metro area dropping the usual rain and hail June 24, 1987.
The Greeley Tribune
A large piece of hail the size of a tennis ball is shown June 27, 1999 from a storm two miles south of Bridgeport, Neb. University of Northern Colorado assistant professors Bruce Lee and Cathy Finley did not spot this storm in time but saw its aftermath. The assistant professors spend their summers chasing tornadoes. The storm-chasing partners do it for research. They gather information to make it easier to produce storm models. The Greeley Tribune,
Craig F. Walker, The Denver Post
A dog named Benny watches an incoming storm from a field on Kobobal Farm in Morgan County, CO. Benny's owner Glen Kobobal says that the dog has had a fear of storms ever since he was struck by a tennis ball size piece of hail during a storm in the summer of 2002. This storm dropped a quarter inch of rain on the farm.
Craig F. Walker, The Denver Post
Dave Benz, of Fox Sports Rocky Mountain files a report from the 18th green. The afternoon Pro-Am tournament of the International at Castle Pines Golf Club came to an end after a violent lightening and hail storm in 2004.
Jerry McBride, The Durango Herald, The Associated Press
Lori Large shovels hail off her front porch, Thursday, Sept. 29, 2005, north of Durango, after a storm moved through the area in the early morning leaving several inches of hail in the lower elevations and snow in the San Juan Mountain's in Southwest Colorado.
RJ Sangosti, The Denver Post
Traffic on Interstate 25 north of Colorado Springs makes its way slowly, Wednesday, May 31, 2006, in the north bound lanes during a hail storm that moved through the area. RJ Sangosti, The Denver Post
Aaron Montoya, The Denver Post
A heavy thunderstorm ripped through Lakewood in 2009. Hail and wind damage affected many buildings in the area. O'Toole's Garden Center in Lakewood suffered heavy damage to its outdoor products. O'Toole's employees from several stores out of the area were called to the Lakewood store to help with the clean-up efforts. The store lost an estimated $250,000 in plants.
Hyoung Chang, The Denver Post
Houses in Green Valley Ranch were damaged by hail from a storm May, 22, 2014.
Karl Gehring, The Denver Post
Chris Collins, left, and Paul Nellis, right, pushed a motorist out of the median on Tower Road June 21, 2014. Hail piled more than a foot high on Tower Road stranded several vehicles following a storm that had both heavy rain and hail. Both men work at the Embassy Suites hotel near the airport.
Denver Post Cyrus McCrimmon
Hail storm hit the Denver metro area on Tuesday, May 20, 2014. At the University of Denver, soccer players Taylor Hunter, left and Reagan Duck for cover as they get pelted by the hail on the soccer field.
AAron Ontiveroz, The Denver Post
A Toyota sits beneath a fallen branch at 12th Avenue and Clayton Street after snow broke many tree branches throughout the city after a heavy spring snow. A spring storm hit Colorado covering much of the state in rain, sleet, hail and snow on Sunday, May 10, 2015.
Kathryn Scott Osler, The Denver Post
Jazmin Parra, right, helps her sister Brisa as the two try and navigate a path through several feet of hail. Jazmin's car was parked up the street and she is trying to get Brisa to school June 5, 2015.
Kathryn Scott Osler, The Denver Post
People along West Alaska Place work to dig their cars out from several feet of hail June 5, 2015.
Kathryn Scott Osler, The Denver Post
Crews from Denver Public Works help a group of men to push a car out from several feet of hail along West Alaska Place June 5, 2015.
RJ Sangosti, The Denver Post
A car is covered with leaves after a fast moving hail storm moved through west Arvada, May 24, 2016.
Andy Cross, The Denver Post
A home near 51st Ave and Clay St., one of many that sustained major hail damage from Monday's storm May 9, 2017 in Denver.
Andy Cross, The Denver Post
A work crew enters Beach Court Elementary school to repair major Monday's hail damage at the school May 9, 2017 in Denver.
Kathryn Scott, The Denver Post
Severe storms hit the metro area bringing hail causing damage to trees, shrubs, and flowers on May 9, 2017 in Denver.
Kathryn Scott, The Denver Post
Severe storms hit the metro area bringing hail causing damage to trees, shrubs, and flowers on May 9, 2017 in Denver.
Kathryn Scott, The Denver Post
Severe storms hit the metro area bringing hail causing damage to trees, shrubs, and flowers on May 9, 2017 in Denver.
Kathryn Scott, The Denver Post
Severe storms hit the metro area bringing hail causing damage to trees, shrubs, and flowers on May 9, 2017 in Denver.
Kathryn Scott, The Denver Post
Severe storms hit the metro area bringing hail causing damage to trees, shrubs, and flowers on May 9, 2017 in Denver.
Kathryn Scott, The Denver Post
Severe storms hit the metro area bringing hail causing damage to trees, shrubs, and flowers on May 9, 2017 in Denver.
RJ Sangosti, The Denver Post
Fred Zietz cleans up after a hail storm on May 9, 2017 in Lakewood.
RJ Sangosti, The Denver Post
Jesus Munoz, of Professional Restoration, hooks up hoses to dry out the Colorado Mills Mall on May 9, 2017 in Lakewood. The mall's roof was damaged in the recent hail storm.
Andy Cross, The Denver Post
Broken windows at Beach Court Elementary School on Tuesday, May 9, 2017. The school was closed for the day to repair damage inside and out due Monday's severe hail storm.
Andy Cross, The Denver Post
A man inspects damage and broken windows inside Beach Court Elementary
School Tuesday morning May 09, 2017. The school was closed for the day to repair damage inside and out due Monday's severe hail storm.
John Leyba, The Denver Post
Hail covers the field as looks on just before the Colorado Rockies versus the Chicago Cubs game on May 8, 2017 in Denver, Colorado at Coors Field. The grounds worked hard to clear some of the hail off the tarp.
John Leyba, The Denver Post
Chicago Cubs fans brave the weather as they wait for the tema to exit the dugout against the Colorado Rockies on May 8, 2017 in Denver, Colorado at Coors Field. Weather moved in and dumped hail covering the field prompting a delay.
John Leyba, The Denver Post
Hail covers the field as a storm blown in to the metro area just before the Colorado Rockies versus the Chicago Cubs game on May 8, 2017 in Denver at Coors Field.
John Leyba, The Denver Post
Hail covers the field as a storm blown in to the metro area just before the Colorado Rockies versus the Chicago Cubs game on May 8, 2017 in Denver, Colorado at Coors Field. The grounds worked hard to clear some of the hail off the tarp.
Seth McConnell, The Denver Post
Golf ball and larger sized hail stones that fell in Edgewater, Colorado causing damage to cars, homes and businesses on May 8, 2017.
RJ Sangosti, The Denver Post
Chelsa Nava checks out the damage to her husband's car in the parking lot of the Colorado Mills Mall on May 8, 2017 in Lakewood. A hail storm moved through the area.
RJ Sangosti, The Denver Post
Priscila Cruz, 11, left, and her mother Kissy Cruz stand outside their car, that was damaged by hail, in the parking lot of the Colorado Mills Mall on May 8, 2017 in Lakewood.
Helen H. Richardson, The Denver Post
People navigate piles of hail along Larimer street on the Metropolitan State University of Denver campus after a pounding hail storm ripped through the area on May 8, 2017 in Denver. The fast moving storm took many by surprise when the storm hit around 3:00.
Helen H. Richardson, The Denver Post
People navigate piles of hail and standing water along Larimer street on the Metropolitan State University of Denver campus after a pounding hail storm ripped through the area on May 8, 2017 in Denver.
Helen H. Richardson, The Denver Post
People navigate piles of hail and standing water along Larimer street on the Metropolitan State University of Denver campus after a pounding hail storm ripped through the area on May 8, 2017 in Denver. The fast moving storm took many by surprise when the storm hit around 3:00.
DENVER, CO - MAY 8: A cyclist waits at a light as he contemplates navigating piles of hail and standing water after a pounding hail storm ripped through the area on May 8, 2017 in Denver, Colorado. The fast moving storm took many by surprise when the storm hit around 3:00. (Photo by Helen H. Richardson/The Denver Post)
Helen H. Richardson, The Denver Post
Workmen cover their heads as they run for cover to get out of the pounding hail storm that hit the metro area around 3:00 on May 8, 2017 in Denver.
Helen H. Richardson, The Denver Post
Hail looks like snow as cars and buses drive slowly down Wewatta street on May 8, 2017 in Denver.
Helen H. Richardson, The Denver Post
Kenny Anderson tries to get out of the pounding hail storm underneath the 20th street bridge on Wewatta street on May 8, 2017 in Denver.
DENVER, CO - MAY 8: People navigate piles of hail along Larimer street on the Metropolitan State University of Denver campus after a pounding hail storm ripped through the area on May 8, 2017 in Denver, Colorado. The fast moving storm took many by surprise when the storm hit around 3:00. (Photo by Helen H. Richardson/The Denver Post)
Helen H. Richardson, The Denver Post
People navigate piles of hail along Larimer street on the Metropolitan State University of Denver campus after a pounding hail storm ripped through the area on May 8, 2017 in Denver.
Helen H. Richardson, The Denver Post
Kenny Anderson tries to keep his umbrella in his hands as the wind blows while trying to keep out of the pounding hail storm underneath the 20th street bridge on Wewatta street on May 8, 2017 in Denver.
Helen H. Richardson, The Denver Post
Amanda Cress holds on tightly to her son Charles, 9, as she and her husband Charles move quickly to get out of the pounding hail storm along Wewatta street on May 8, 2017 in Denver.
Ken Lyons, The Denver Post
Hail piles up on Colfax Ave. outside Civic Center Park in downtown Denver Monday afternoon, May 8, 2017.
The largest hailstone ever recorded in America spent close to an hour aloft in a cloud growing to the size of a small volleyball, then plunged to earth at more than 100 mph, struck the ground in South Dakota weighing nearly 2 pounds, left a divot, was scooped up by a local rancher and placed in a freezer, melted a bit during a power outage, was packed in dry ice and driven cross country, and finally arrived at a lab in Boulder where Charles Knight, one of the nation’s premier authorities on hail, added it to a research collection that also included the two previous record-setting hailstones.
“Large hail is pretty rare this close to the Front Range,” said Knight, a senior scientist at the National Center for Atmospheric Research. “It’s really pretty rare anywhere.”
But when the clouds twirl just right, Colorado’s unique geography and climate are capable of producing spectacular amounts of hail.
The state resides in what meteorologists call “Hail Alley,” a swath of land that also includes parts of Nebraska and Wyoming that is frequently bedeviled by hail. Areas of the Front Range and Eastern Plains can see 10 or more days of severe hail per year, on average. A study published last year by the National Insurance Crime Bureau ranked Colorado second nationally, behind Texas, for hail loss claims between 2013 and 2015.
And if it sometimes seems like hail is nature’s way of betraying you, there’s a reason.
The science of hailstone formation reveals that you have been told a lie your whole life: Water — really, really pure water — doesn’t necessarily freeze at 32 degrees Fahrenheit. It can, in fact, stay in liquid form at temperatures down to almost minus-40 F, a phenomenon that scientists call “supercooled water.”
It’s these tiny droplets of supercooled water, suspended in clouds towering as much as 9 miles above the ground, that start joining together to form hail. But first they need an instigator because supercooled water, Knight said, “doesn’t know how to start forming molecules into ice crystals.”
The instigator could be a fleck of dust that changes a droplet’s structure or a speck of water that freezes spontaneously at a colder elevation, said Andrew Heymsfield, a hail expert and colleague of Knight’s at NCAR. Either way, once there is an ice particle in the cloud — what scientists call a “hail embryo” — it exerts a kind of chemical peer pressure on other droplets, pulling them in, turning them into ice and gradually building up a hailstone.
It’s a process seemingly dreamed up by Kurt Vonnegut, who once authored a novel about a chemical that turns water irresistibly into ice. Being told this, Heymsfield chuckled to himself and then said something that sounded like a joke but is actually true.
“Well,” he said, “his brother, Bernie Vonnegut, was prominent in our field.”
So what does this have to do with Colorado?
The Front Range’s topography turns out to be a perfect petri dish in which to create hail.
Hailstones don’t form or grow very big without massive amounts of air billowing up from below. These updrafts keep the embryonic stone aloft long enough to gather up water into an ice ball, and the stronger the updraft, the bigger the stones can grow. Heymsfield said hailstones can spend a half hour forming in clouds, with the absolute largest in the strongest updrafts taking close to an hour.
Mountainous areas — such as Colorado’s Rockies — promote these updrafts by acting as elevated heat sources that pump warm air from the ground high up into the atmosphere. These storms might at first loom over Colorado but they also carry out onto the plains to the east, sucking in more moisture as they go.
Updrafts, though, only go so far in forming hail. The air needs to stay cold enough closer to the ground for the hail to actually fall as ice instead of melting on the way down.
This is why, Heymsfield said, some of the biggest hail comes from storms not in warm southern states like Florida that can produce huge thunderstorms but in comparatively cooler South Dakota and Nebraska. On Monday, the day the hailstorm struck the metro area, the temperature in Denver topped out in the 70s. The day the record hailstone fell — on July 23, 2010, near Vivian, S.D. — the high temperature barely crested into the 80s, well below average for the date.
To his dismay, that record hailstone hung around Knight’s lab only for a few months. After making a model, Knight returned it to the rancher who found it.
“I would have wanted to slice it up and see what the layering looked like and what the crystal structures looked like,” he said. “But he wanted it back, so we sent it back to him.”
Knight never learned what the rancher planned to do with it — though the rancher once joked about using it to make a daiquiri. When last seen, by a Wall Street Journal reporter in 2011, the hailstone was still intact, living out its retirement in the rancher’s Montgomery Ward freezer.
