Hail
Hail is a kind of solid precipitation, different from ice pellets. It includes balls or irregular lumps of ice, each of which is known as a hailstone. Ice pellets generally fall in cold weather whereas the growth of hail is immensely constrained at cold surface temperature. In contrast to ice pellets, hailstone usually measures between 5 mm (0.2 in) and 15 cm (6 in) in diameter. Hailstone is most commonly found in mid-latitudes and usually lasts around 15 minutes. They generally occur in mid - to -late afternoon.
Hail is extremely destructive to crops and buildings if large enough, or it may be even dangerous to animals exposed to it.
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Hailstorm Definition
Any thunderstorm through which hail is produced and reaches the ground is known as a hailstorm. Hail has a diameter of 5 mm (0.20 in) or more and can grow to 15 cm (6 in) and weighs more than 0.5 kilograms.
In contrast to ice pellets, a hailstone is stratified and can be irregular and clustered together. Hail consists of transparent ice and alternating layers of transparent and translucent ice at least 1 mm ( 0.039 in) thick, which are laid down upon the hailstone as it travels through the clouds, held off above by air with strong upward motion until its weight exceeds the updraft and falls to the ground.
The diameter of hail is generally varied, in the United States, the damaged hail, on average, is observed between 2.5 cm (1 in) and golf ball-sized ( 1.75 in). Stones larger than (0.80 in) are considered to be large enough to cause damage.
Hailstone Formation
Hailstone formation or hail formation occurs when the rain droplets are carried upward through thunderstorm updraft into immensely cold areas and freezes. Hailstones then further grow by hitting liquid water droplets that freeze into the surface of the hailstone. If the water freezes speedily when hitting the hailstone, cloudy ice will form as the air bubbles will be confined in the newly formed ice. However, if the water evaporates slowly, the air droplets will escape and the newly formed ice will be clear. The hails fall when thunderstorm updraft can no longer support thunderstorms weight, which can come about if the stone becomes large enough or the updraft weakens.
Hailstone Meteorology Size
The hailstone size can be best described by measuring the diameter using a ruler. In the absence of a ruler, the hailstone size can be best estimated by comparing its size to that of known objects, known as coins. Comparing the hailstone size using the objects such as eggs, peas, marbles is imprecise due to the varied dimensions. The UK organization, TORRO also measures for both hailstone and hailstorms.
When observing the hail at an airport, METAR code is used within the surface observation which is related to the size of the hailstone. The GR within the metric code is used to represent the larger hail, of a diameter of the latest 0.25 inches (6.4 mm).
The terminal velocity of hail or the speed at which hailstone is falling when striking the ground changes. It is estimated that a hailstone of 1 cm (0.39 inches) in diameter falls at a rate of 9 meters per second (20 mph) while the stone size of 8 cm (3.1 inches) in diameter falls at a rate of 48 meters per e camph. The speed of hailstone cannot be determined accurately as they are not in spheres.
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Did You Know?
Hailstone can fall at a speed between 9 mph (14 km/hr) and 110 mph (17 km/hr).
The larger hailstones are faster to fall.
The hailstorm most commonly occurs in one of the areas of the United States known as the hail alley.
Hailstorms are formed when thunderstorms carry rain droplets up into the extremely cold areas of the Earth's atmosphere.
Approximately 200 to 600 nomads seem to have died of injuries. The haistone of thel size of a cricket ball occurred around the 9th century in Roopkund, Uttarakhand, and India.
FAQs on Hail Meteorology
1. What is hail in the context of meteorology?
In meteorology, hail is a form of solid precipitation consisting of balls or irregular lumps of ice called hailstones. These hailstones are exclusively produced by cumulonimbus clouds (thunderstorms) and are typically between 5 millimetres to 15 centimetres in diameter. Unlike other forms of ice precipitation like sleet, hail is formed by layers of ice accumulating as it is cycled through intense updrafts and downdrafts within a storm.
2. How does hail form inside a thunderstorm?
Hail formation is a multi-step process that relies on the powerful vertical air currents within a thunderstorm. The process includes:
Updrafts: Strong currents of rising air, or updrafts, carry water droplets high into the extremely cold regions of a cloud.
Freezing: These droplets, known as supercooled water (liquid water below 0°C), freeze onto a condensation nucleus, such as a dust particle, forming a tiny ice pellet.
Growth: The hail embryo is tossed up and down within the cloud. As it rises, it accumulates more supercooled water which freezes onto its surface, adding layers of ice. The hailstone continues to grow until its weight is too heavy for the updraft to support.
Descent: Finally, the heavy hailstone falls from the cloud, reaching the ground as solid ice.
3. What are the common classifications for hail size?
Hail is officially classified by its diameter. Meteorologists often use comparisons to everyday objects to describe its size. A thunderstorm is officially classified as 'severe' by meteorological agencies when it produces hail with a diameter of 1 inch (2.54 cm) or greater. Common size comparisons include:
Pea size: 0.25 inch diameter
Marble size: 0.50 inch diameter
Quarter size (Severe Hail): 1.00 inch diameter
Golf Ball size: 1.75 inch diameter
Softball size: 4.50 inch diameter
4. What is the difference between hail, sleet, and freezing rain?
While all are forms of wintery or cold-weather precipitation, their formation process is distinct:
Hail: Forms in strong thunderstorm updrafts, growing in size within the cloud and falling as a solid lump of ice. It is often associated with warm seasons.
Sleet: Starts as a snowflake, partially melts into a raindrop as it falls through a layer of warmer air, and then refreezes into a small ice pellet before hitting the ground.
Freezing Rain: Falls as a liquid raindrop all the way to the surface and then freezes upon contact with surfaces that are at or below freezing temperature (0°C), creating a coat of ice.
5. Why do most hailstorms occur in the spring and summer, not in the winter?
This is a common point of confusion. Hail formation depends not just on cold temperatures, but on strong atmospheric instability and powerful updrafts. These conditions are created by intense surface heating, which warms the air near the ground and causes it to rise rapidly. This process is most prevalent during the spring and summer months, fuelling the tall, violent cumulonimbus clouds necessary to produce large hail. In contrast, winter air is generally more stable and lacks the strong convective energy needed to support the vertical growth of hailstones.
6. What are the major impacts and effects of a severe hailstorm?
Severe hailstorms can be highly destructive, causing significant damage across various sectors. The primary effects include:
Agricultural Damage: Hail can completely destroy crops such as corn, wheat, soybeans, and fruits, leading to massive economic losses for farmers.
Property Damage: It can shatter windows, dent vehicles, and damage roofs and siding on buildings.
Danger to Life: Large hailstones, especially those the size of a golf ball or larger, can cause serious injuries or even be fatal to people and livestock caught outdoors.
Aviation Hazard: Hail is extremely dangerous for aircraft, capable of causing dents, cracking windshields, and damaging engines, forcing pilots to navigate around hailstorms.
7. What can the internal structure of a hailstone tell us about its formation?
The internal structure of a hailstone provides a record of its journey within a thunderstorm. When a hailstone is cut open, it reveals concentric layers of ice, similar to the rings of a tree. These layers have different appearances:
Opaque Layers: These milky, whitish layers form when supercooled water droplets freeze instantly onto the hailstone in the very cold upper parts of the cloud, trapping tiny air bubbles.
Clear Layers: These transparent layers form in the 'wetter' and slightly warmer parts of the cloud, where water collects more slowly and freezes with fewer trapped air bubbles.
By analysing these layers, meteorologists can understand the number of times the hailstone travelled up and down within the storm's updrafts and the different conditions it encountered.
