Two years ago, a severe storm in Argentina produced hailstones reaching 9 inches wide, prompting meteorologists to propose an entirely new term: “gargantuan hail.” Scientists don’t fully understand how such enormous balls of ice can take shape, but the 2018 storm is providing some tantalizing new clues.
New research in the Bulletin of the American Meteorological Society describes a supercell storm that struck Argentina on February 8, 2018. The storm is notable in that it produced unusually large hailstones, the biggest of which measured 9.3 inches (23.7 cm) in diameter.
The storm is also noteworthy because it struck the densely populated city of Villa Carlos Paz in Córdoba Province. This resulted in numerous sightings and images posted to social media, allowing the authors of the new paper, Matthew Kumjian and Rachel Gutierrez from Pennsylvania State University, to chronicle and study this extreme weather event in detail.
Currently, the U.S. National Weather Service uses the terms “sub-severe,” “severe,” and “significantly severe” to describe the size of hailstones. More informally, some scientists use the term “giant” to describe hail larger than 3.9 inches (10 cm). Kumjian and Gutierrez are now asking to have this meteorological guitar amp cranked to 11: They propose the term “gargantuan hail” to describe the “upper extreme of hail sizes,” as they write in their paper, specifically referring to ice stones larger than 6 inches (15 cm).
“We feel that the community shall decide whether or not this new term will stick, so it is a democratic process,” Kumjian told Gizmodo. “The National Weather Service can use the term if they would like, and it may happen organically at local offices. Because these are relatively rare events, my guess is that we won’t see this appear in any warning text anytime soon. But, it may be useful for reporting of exceptionally large hailstones, and we hope it may spur more research into these extreme storms.”
Following the 2018 storm in Argentina, and in addition to collecting online accounts and images of the event, the researchers visited Villa Carlos Paz, where they interviewed residents to learn more about the storm and the shockingly large hail. They also collected data gathered by a monitoring station that tracks storms with C-band radar, which they used to simulate the storm in a computer model.
The new paper documents the unique meteorological conditions that churned within this storm—insights that could eventually lead to an improved ability to predict hailstorms. This would obviously be a good thing, given the propensity of large hail to damage crops, property, and human heads.
Three hailstones of note were documented in the new study, including a 4.5-inch chunk (11.38 cm) that a local resident smartly and hurriedly placed inside their freezer for safekeeping. The other two enormous hailstones of note measured 7.4 and 9.3 inches wide (18.8 and 23.7 cm) and were documented and measured based on photographic evidence.
The largest of these three gargantuan hailstones is very close to the world record, an equally sized hailstone that fell onto Nebraska in 2003. Four years ago, a storm chaser in Oklahoma reported a hailstone measuring 7.9 inches (20 cm) wide, but this example remains unofficial as it wasn’t fully corroborated, according to the new paper.
Storms that produce big hail are called supercells and feature persistent, strong, and rotating updrafts. These vertical winds are critical to the process, as they carry burgeoning hailstones through the frigid air, allowing them to grow even larger. That said, scientists still don’t fully understand how storms are able to produce giant and gargantuan hailstones, but Gutierrez, who is currently writing her master’s thesis on the subject, has some ideas.
“Rachel’s research suggests that the supercell storms that produce gargantuan hail have stronger rotation in their updrafts than supercell storms producing smaller hail,” explained Kumjian.
This connection has been documented before in smaller size categories, but Gutierrez’s research extends this relationship to the gargantuan category.
“We are trying to understand the physics behind this correlation. It may be that the strong rotation has a direct influence on the hail pathway through the updraft that leads to extreme growth or longer times spent in the growth region,” said Kumjian. “Or, it could be that the strong rotation is a byproduct of environmental factors and/or storm internal processes that are also favorable for very large hail, but the rotation itself is not directly responsible for the hail growth.”
More work needs to be done, and also more data collected from these extraordinary storms. These events are rare, but Kumjian believes they may be more common than we think. The ongoing use of social media and even drone technology could assist with this line of research.
“We implore citizen scientists to help us out by photographing hailstones with reference objects or rulers, and even weighing the stones on a kitchen scale!” said Kumjian. “The more cases we can obtain, the more we can learn about the processes going into making such extreme hail.”