A hailstorm can turn a summer afternoon violent in minutes, pelting rooftops and cars with ice hurled down from towering clouds. In the most extreme cases the ice arrives not as harmless pea-sized pellets but as jagged spheres the size of grapefruit, capable of shattering windshields, denting metal, and injuring anyone caught outdoors. Stones that large fall from the sky at highway speeds, striking with a force that can crack tempered glass and leave lasting dents in a car’s roof and hood within seconds.
How a hailstone grows inside a storm
Hail begins when raindrops are swept high into a thunderstorm by rising air and carried into a zone where the temperature plunges far below freezing. There the droplets turn to ice, and as they tumble through the cloud they collide with supercooled water that freezes onto their surface in layer after layer, thickening the stone as it goes.
The National Weather Service explains that a hailstone keeps growing as long as the storm’s upward rush of air can hold it aloft, and it only falls once it becomes too heavy to be suspended. That relationship between weight and updraft is the key to why some hail stays tiny while other stones grow monstrous, a process detailed in the agency’s hail safety guidance.
Why the strongest storms make the biggest stones
The size of a hailstone is a direct measure of the storm’s power. Weak updrafts can support only small ice, but the intense, rotating updrafts of a supercell thunderstorm can suspend a stone repeatedly, lifting it back into the frigid upper cloud again and again so it accumulates more ice with each pass.
According to NOAA’s National Severe Storms Laboratory, hail two inches across or larger is generally tied to supercells, the most organized and long-lived form of thunderstorm. It takes an exceptionally strong updraft, moving upward at highway speeds, to grow and hold the grapefruit-sized stones that make headlines.
The scale forecasters use
Meteorologists commonly describe hail by comparing it to familiar objects, from peas and quarters to golf balls, baseballs, and grapefruit. A grapefruit-sized stone can measure four inches or more in diameter, and the largest documented hailstones in the United States have exceeded even that, weighing close to a pound.
Those size comparisons are not just colorful language. They give storm spotters and warning meteorologists a fast, shared vocabulary for reporting what is falling, which in turn helps forecasters gauge a storm’s intensity and issue timely alerts to communities in its path. A report of golf-ball or baseball-sized hail tells a forecaster that a storm’s updraft is unusually strong, information that can sharpen warnings for the damaging winds and tornadoes such storms sometimes produce.
The rings hidden inside a hailstone
Cut a large hailstone in half and it often reveals a pattern of concentric layers, alternating between clear and cloudy ice. Each layer records a pass through a different part of the storm, laid down as the stone collided with water droplets under changing conditions of temperature and moisture.
When water freezes quickly onto the stone, trapped air bubbles make the ice appear milky, while slower freezing lets the bubbles escape and produces clear ice. Reading those rings is a bit like counting the growth of a tree, giving scientists a physical record of how many times the stone was lifted and how turbulent its journey through the cloud really was.
Where the biggest hail falls
Giant hail is not spread evenly across the map. In the United States it clusters in a corridor sometimes called Hail Alley, spanning parts of Colorado, Nebraska, Wyoming, and neighboring states, where high elevation and the right mix of moisture and instability set the stage for powerful, hail-producing storms.
High plains and mountain-adjacent regions are especially prone because storms there tap into strong updrafts while the freezing level sits closer to the ground, giving stones less time to melt as they fall. Similar hail-prone zones exist in other parts of the world, but the central United States sees some of the most frequent and destructive large-hail events anywhere.
The damage giant hail leaves behind
Large hail is among the costliest forms of severe weather. Stones of that size fall fast enough to crack roofs, punch through skylights, strip siding, total vehicles, and flatten crops across wide swaths of farmland, and severe hail events routinely cause billions of dollars in damage in a single season.
The danger to people is real as well. Anyone caught in the open during a giant-hail event faces a genuine risk of serious injury, which is why forecasters urge residents to move indoors and away from windows the moment a severe thunderstorm warning mentions the threat of damaging hail.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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