Hail is a type of solid precipitation that forms during thunderstorms. It consists of balls or irregular lumps of ice, known as hailstones. Unlike snow and sleet, hail is most common in the warmer months when strong thunderstorms are more frequent. Hail is a type of solid precipitation associated with thunderstorms that consists of irregular lumps or rounded balls of ice.
The formation of hail is a complex process involving several steps, primarily occurring within cumulonimbus clouds during thunderstorms. It begins with strong updrafts – upward moving air currents – that carry raindrops into the colder regions of the cloud, where temperatures are below freezing. Once the raindrops reach these cold areas, they freeze into tiny ice particles. These ice particles then undergo a series of ascents and descents within the cloud, carried by the storm’s updrafts and gravity. As they move, they collide with supercooled water droplets – liquid water below freezing temperature. This causes a process called accretion, where the supercooled droplets freeze onto the ice particle, making it grow in size.
Dry growth also occurs, where the outer surface freezes yet accumulates more mass. Wet layers are translucent, while dry layers are opaque and contain trapped air bubbles. This process repeats, with the hailstone growing larger with each cycle until it becomes too heavy for the updrafts to support. At this point, it falls to the ground as hail.
The key factors for hail formation include:
Sufficient Cloud Height: Higher clouds allow more time for hailstones to grow before falling. So, cumulonimbus clouds are the type that produces hail;
Strong Updrafts: Powerful updrafts lift the hailstones high into the cloud for further; growth;
Abundance of Supercooled Water: Clouds containing a lot of moisture provide the material for the hailstones to grow. While lightning does not cause hail storms, cloud-to ground lightning is common when they occur.
Hail and tornadoes are both weather phenomena commonly associated with severe thunderstorms, particularly those involving super cells, which are highly organized, rotating thunderstorms. While they are distinct events, they often occur in the same storm. Both hail and tornadoes typically form in environments where there is strong instability in the atmosphere, a significant difference in wind speed and direction with altitude (wind shear), and ample moisture. These conditions favor the development of powerful thunderstorms capable of producing both hail and tornadoes. A green sky is indicative of conditions ripe for hail or tornado formation.
The presence of large hail in a storm indicates the potential for tornado formation. This is because the same strong updrafts needed to support large hailstones are also a key component in the development of tornadoes. In a typical super cell thunderstorm, hail often falls near the storm’s updraft region, while tornadoes usually form in the downdraft area, near the rear of the storm. However, tornadoes can occur before, after, or at the same time as hail, depending on the storm’s dynamics. Despite the correlation, not all storms that produce hail will produce tornadoes, and vice versa.
Hailstones fall at speeds varying from 44 to 72 mph (70 to 116 km/h). Factors affecting the fall speed include: Size and Weight of the Hailstone: Larger, heavier hailstones fall faster; Shape and Density: Irregular shapes slow down the fall; Wind and Updrafts: Air currents influence the trajectory and speed. Hailstones range from pea-sized (1/4 inch or 6 mm) to as large as grapefruits (4.5 inches or 114 mm). For perspective, common comparisons include: Pea-sized (1/4 inch); Marble-sized (3/4); Golf ball-sized (1.75 inches); Tennis ball-sized (2.5 inches) ;Grapefruit-sized (4.5 inches).
While hail, graupel, sleet, and snow are all forms of frozen water, there are differences between them: Hail forms in thunderstorms with repeated cycles of ascending, freezing, and accreting. Hailstones are larger than
Graupel, sleet, or snowflakes. Graupel also known as soft hail, forms when supercooled water droplets coat a snowflake, creating a soft, spongy ball. Graupel is smaller than hail and forms in weaker updrafts. Sleet or ice pellets form when raindrops freeze as they fall through a cold layer of air near the ground. Sleet is smaller and more translucent than hail.
Snow forms when water vapor in a cloud freezes directly into ice crystals, bypassing the liquid phase. Snowflakes have intricate, symmetrical patterns and are much softer and less dense than hail. Of course, the other significant difference is that graupel, sleet, and snow are generally cold weather events. Thunderstorms that produce hail do sometimes occur in winter, but mainly they are warm weather phenomena.
Some countries experiment with hail suppression methods, such as cloud seeding. This involves releasing substances like silver iodide into clouds to prevent hailstones from growing large. In the middle ages, efforts involved ringing church bells and firing cannons. The thinking was that the vibrations would prevent large hail formation. However, thunder produces greater sonic waves and does not dispel hail.
A hailstorm is extremely hazardous for aircraft, which can be seriously damaged if caught in the middle of a severe hailstorm. Flights can also suffer damage upon landing on runways with accumulated hail. Hail is not only harmful to aircraft in the sky, but also equally dangerous for automobiles on the road. Falling hailstones can shatter windows and windshields of vehicles. Visibility is also greatly reduced during a hailstorm and roads become slippery. Therefore, driving during a hailstorm can be extremely dangerous. Hailstorms are highly destructive in nature. Since hailstones fall from great heights at high speeds, they can easily penetrate through glass-roofed structures or skylights.
Although metallic surfaces are less prone to damage by hailstones, dents are often created by the falling ice. The metallic bodies of automobiles can also get dented by hail. Thus, a severe hailstorm can lead to economic losses in terms of damage to buildings and vehicles. Perhaps one of the most destructive effects of hailstorms can be observed on farms.
A hailstorm with powerful winds can physically damage crops across large areas. The falling hailstones and strong winds bend and break plants and strip them of leaves and bark. Thus, farmers suffer heavy losses during such storms. Months of hard work by farmers can be destroyed almost instantly. It is possible for hailstones of significant size to kill an adult who is unable to find cover during a hailstorm. Massive hailstones are known to cause fatal head trauma or concussions. It is believed that about 200 to 600 nomads of a tribe died in Roopkund, Uttarakhand, India, during a severe hailstorm centuries ago.
Their recently discovered skeletons with head injuries appear to support this historical account. At around 1.30 pm on May 5, 2024, Imphal valley was marred by heavy hailstorms which devastated many houses, vehicles, vegetable farms and made many homeless. Rising global temperatures might be causing hailstorms to become more violent, with larger chunks of ice and more intense downpours. But just how big can a hailstone get?
