Hail is precipitation made of balls or irregular lumps of ice that form inside thunderstorms.
Hail develops in powerful updrafts, where supercooled water droplets collide with ice embryos and freeze onto them. If the updraft is strong enough, the growing hailstone can remain suspended and collect additional layers of ice. It eventually falls when its weight exceeds the storm’s lifting force.
Hailstones can be small as peas or several centimetres across. The largest officially measured hailstone by diameter in the United States fell near Vivian, South Dakota, in 2010, measuring 20.3 centimetres across. Size depends on storm structure, water supply, and the duration of growth.
Hail is different from sleet, which consists of small ice pellets formed when raindrops or melted snow refreeze near the ground. Graupel is softer and usually forms when supercooled droplets coat snow crystals.