This is what’s known as “gargantuan hail,” a potential record-smashing form of hailstone created by a violent thunderstorm that rocked Argentina in 2018.
Researchers from Penn State have recently been studying the hailstones that pelted down on the Argentinian city of Villa Carlos Paz on February 8 2018. Reported in the Bulletin of the American Meteorological Society, one particularly chunky hailstone is thought to have measured between 18.7 and 23.6 centimeters (7.4-9.3 inches) across.
Hailstones are chunks of ice that form when drops of water freeze together in the chilly upper regions of thunderstorm clouds. The hailstones grow larger as they move up and down in the thunderstorm updraft, catching more water and creating new layers of ice through every journey. Eventually, when the thunderstorm's updraft can no longer support the weight of the hailstone, it falls to Earth.
For the new study, the researchers pieced together the story of Argentina's giant hailstones using witness testimonies, photographers, site visits, meteorological data, and the storm’s observed radar signatures. They found the storm updraft's rotational velocity (essentially how fast it is spinning) appears to have some connection to the size of large hailstones, although the link is not well understood. In light of their study, the researchers proposed hail larger than 15 centimeters (6 inches) should be classified as "gargantuan."
“The storm was a 'supercell, a class of strong, long-lived storms characterized by a persistent, rotating, updraft,” Matthew Kumjian, lead study author and associate professor in the Department of Meteorology and Atmosphere Science at Penn State, told IFLScience.
“Supercells tend to have very strong, broad updrafts, which is important for growing large hail. The airflow patterns in the storm allow precipitation particles to take long paths across the updraft, which maximizes their time spent in the favorable region for hail growth,” he explained.
Regardless of the finer details, one thing is more certain: gargantuan hail can cause some serious damage. The study details a bunch of different damaged properties in Argentina relayed from eyewitnesses, including dented cars and battered rooftops across the city. The researchers also recall how giant hailstones have previously been documented falling through roofs and multiple floors in a building.
“As far as we know, there were no serious injuries, thankfully,” added Kumjian.
The largest of the documented hailstones from the Argentinian supercell storm appears to beat the current official record holder, a 20.3-centimeter (8-inch) wide hailstone that fell near Vivian, South Dakota on June 23 2010. Unfortunately, however, the researchers won’t be able to get the hailstone into the Guinness Book of Records as the physical remains have long melted away.
“There is no physical specimen to officially measure, so the estimate remains only an estimate. I don't think it would be desirable to change the standards used to keep the records. Alas! But it is for the best to keep the conventions consistent for our records,” concluded Kumjian.