The largest officially recognized piece of hail fell in South Dakota, weighing in at almost 2 pounds with an 8 inch diameter.
That was back in July 2010. Meanwhile, on the other side of the Atlantic, the largest hailstone ever recorded in Europe was in July 2023 in the village of Azzano Decimo in Northern Italy, clocking in at 19 cm (7.5 inches).
We have all learnt that hail comes in lots of shapes and sizes, but what is the reason that some hailstones become so large? Well, it's to do with the science of storms. According to Brian Tang, an atmospheric scientist, hail begins as tiny crystals of ice that are swept into a thunderstorm’s updraft. As these ice embryos collide with supercooled water - liquid water that has a temperature below freezing - the water freezes around each embryo, causing the embryo to grow.
Supercooled water freezes at different rates, depending on the temperature of the hailstone surface, leaving layers of clear or cloudy ice as the hailstone moves around inside a thunderstorm. If you cut open a large hailstone, you can see those layers, similar to tree rings.
The path a hailstone takes through a thunderstorm cloud, and the time it spends collecting supercooled water, dictates how large it can grow.
Rotating, long-lived, severe thunderstorms called supercells tend to produce the largest hail. In supercells, hailstones can be suspended for 10 to 15 minutes or more in strong thunderstorm updrafts, where there is ample supercooled water, before falling out of the storm due to their weight or moving out of the updraft.
Image credit: ERZ via Wikimedia Commons, CC BY