'Gargantuan' Hail Pelted a City in Argentina—and One Stone May Have Broken the World Record

On February 8, 2018, the city of Villa Carlos Paz in northern-central Argentina was struck by a supercell thunderstorm that produced giant hailstones. Now, researchers say that some of these "gargantuan" ice pellets may have broken the world record for hailstone size.

According to a study published in the journal Bulletin of the American Meteorological Society, one of the hailstones produced by the storm is estimated to have measured between 7.4 and 9.3 inches across, which is close to or exceeds the world record for maximum dimension.

"It's incredible," Matthew Kumjian, an author of the paper from the Department of Meteorology and Atmosphere Science at Penn State, said in a statement. "This is the extreme upper end of what you'd expect from hail."

The current record is held by an 8-inch-wide hailstone that fell near Vivian, South Dakota in July 2010.

Observations of gargantuan hail—defined as greater than 6 inches in maximum dimension—are quite rare. However, the fact that the hailstones in Argentina fell on an urban center, with a population of more than 50,000 people, provided the scientists with an exceptional opportunity to study the phenomenon.

During the storm, numerous residents shared pictures and videos of the event on social media, documenting numerous large hailstones. About a year later, the authors began their investigation, interviewing local residents, examining social media images and analyzing radar observations from the storm.

Part of their research involved using a technique called photogrammetry, which involved estimating the size of hailstones by analyzing photographic evidence.

gargantuan hailstone
A gargantuan hailstone that fell in Argentina may have broken the world record. Victoria Druetta

In the study, the authors document three notable hailstones from the storm. These were one measuring up to 4.5 inches across that was preserved in a freezer and scanned with a 3D infrared scanner; another 7.1-inch stone; and the potentially record-setting example measuring between 7.4 and 9.3 inches across. The researchers estimated the size of the latter stone using photogrammetry.

According to the researchers, the latest results cast new light on the potentially dangerous phenomenon of gargantuan hail—and could have implications for public safety.

"Anything larger than about a quarter in size can start putting dents into your car," Kumjian said. "In some rare cases, 6-inch hail has actually gone through roofs and multiple floors in houses. We'd like to help mitigate the impacts on life and property."

"Such a well-observed case is an important step forward in understanding environments and storms that produce gargantuan hail, and ultimately how to anticipate and detect such extreme events," Kumjian said.

Hail is a form of precipitation consisting of solid ice pellets that form inside thunderstorm updrafts, according to the National Severe Storms Laboratory (NSSL).

"Hailstones are formed when raindrops are carried upward by thunderstorm updrafts into extremely cold areas of the atmosphere and freeze. Hailstones then grow by colliding with liquid water drops that freeze onto the hailstone's surface," a description on the NSSL website reads.

"If the water freezes instantaneously when colliding with the hailstone, cloudy ice will form as air bubbles will be trapped in the newly formed ice. However, if the water freezes slowly, the air bubbles can escape and the new ice will be clear. The hail falls when the thunderstorm's updraft can no longer support the weight of the hailstone, which can occur if the stone becomes large enough or the updraft weakens."