Day of horror in Spain! People are being saved from huge hailstones from the sky!

Any thunderstorm that causes hail to reach the ground is called hail. An ice crystal larger than 5 mm (0.20 in) in diameter is considered a hailstone. Hailstones can grow up to 15 cm (6 in) and weigh over 0.5 kg (1.1 lb).

Unlike ice pellets, hailstones are layered, may be irregular in shape and stick together. Hail consists of clear ice or alternating layers of clear and translucent ice at least 1 mm (0.039 in) thick, which are deposited on the hailstone as it moves through a cloud suspended in air with strong upward motion until its weight overcomes the updraft and will fall to the ground. While hail diameters vary, in the United States, the average hail size that causes damage ranges from 2.5 cm (0.98 in) to 4.4 cm (1.75 in) golf ball size.

Stones larger than 2 cm (0.80 in) are generally considered large enough to cause damage. The Canadian Meteorological Service issues severe thunderstorm warnings when hail of this size or greater is expected. The US National Weather Service has set a diameter threshold of 2.5 cm (0.98 in) or more as of January 2010, exceeding the previous threshold of 0.75 in (1.9 cm) deg. In other countries, thresholds vary depending on local sensitivity to hail; for example, smaller hailstones can negatively impact grape growing areas. Hailstones can be very large or very small, depending on how strong the updraft is: weaker hailstones produce smaller hailstones than stronger hailstones (e.g. supercells), as stronger updrafts in a stronger storm can hold larger hailstones in the air.