Hail forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing (< 32 °F (0 °C)). The growth rate is maximized at about -13 °C (9 °F), and becomes vanishingly small much below -30 °C (-22 °F) as supercooled water droplets become rare. For this reason, hail is most common in midlatitudes during early summer where surface temperatures are warm enough to promote the instability associated with strong thunderstorms, but the upper atmosphere is still cool enough to support ice. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the midlatitudes because the atmosphere over the tropics tends to be warmer over a much greater depth.
Also, entrainment of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Hail is also much more common along mountain ranges because mountains force horizontal winds upwards (known as orographic lifting), thereby intensifying the updrafts within thunderstorms and making hail more likely.
One of the most notorious regions for large hail is northern India and Bangladesh, which have reported more hail-related deaths than anywhere else in the world and also some of the largest hailstones ever measured. China is also notorious for killer hailstorms.
Certain locations in North America (such as the area around Calgary, Alberta) have gained the nickname "Hailstorm Alley" among meteorologists for the frequency of hailstorms and their severity. Hailstones, while most commonly only a few millimetres in diameter, can sometimes grow to 15 centimetres and weigh more than half a kilogram (1.1 pounds).
Pea or golfball-sized hailstones are not uncommon in severe storms. Hail can do serious damage, notably to automobiles, skylights, glass-roofed structures, and most commonly, farmers' crops. Rarely, massive hailstones have been known to cause concussions or fatal head trauma. Sometimes, hail-producing clouds are identifiable by their green colouration.
Ok now since you all know what is a hail strom now lets look at what kinda damages a hail strom can cause :
And this is the kinda damages these hails is capable of inflicting :
Automobiles and cars is the main victim ..... it doesnt matters whether its moving or not.