Hail is one of four types of precipitation that falls from the sky. It’s also the most dangerous, damaging type, occurring during severe storms. Read more to learn the definition of hail, how hail forms, and what causes hail.
Introduction to Hail
A summertime thunderstorm is incredibly dramatic to watch. You can sense the temperatures shifting from warm to cool and feel rain on your skin. The winds change direction, and thunder rumbles in the distance.
Lightning streaks across the sky. In a very severe thunderstorm, pieces of ice fall to the ground in the form of hail.After a storm that includes hail, people often come outside and are bewildered to see balls of ice covering outdoor surfaces.
They might also be shocked to see damage from hail, which sometimes results in cracked car windshields and dents in the siding of houses. According to the National Oceanic and Atmospheric Administration, hail causes over one billion dollars of damage in the United States each year.
Definition of Hail
So now you know what hail can do, but what exactly is it? Hail is a form of precipitation that falls as ice pellets during a severe thunderstorm. If hail measuring larger than 0.75 inches in diameter falls during a thunderstorm, it is classified as severe weather. Sometimes damaging winds accompany this type of storm as well.
Meteorologists like to use common objects to estimate the size of hail in their forecasts. Hail can fall in small pieces, such as the size of a pea (0.25 inches) or marble (0.5 inches). It can also form in larger chunks, like the size of a quarter (1 inch), golf ball (1.
75 inches), baseball (2.75 inches), or even a grapefruit (4 inches).On July 23, 2010, in Vivian, South Dakota, a record-breaking hailstone fell to the ground.
An observer saw a huge ball of ice that had fallen during the storm and rushed to freeze it. At 8 inches in diameter and nearly 2 pounds, this is the largest hailstone ever recorded in the United States!But hail doesn’t have to be large to be damaging. Small, pea-sized hail can completely wipe out a young crop growing in fields and be a costly loss for the farmer. Large, softball-sized hail can be fatal for livestock and humans, as well as shatter glass in homes and businesses and total vehicles. Though human fatalities are rare, in May of 1986, 100 people were killed and over 9,000 people were injured in China by a major hailstorm. The parts of the United States most affected by hail and severe storms include Wyoming, Colorado, and Nebraska. Areas of the world where hail is common includes Northern Italy, and parts of India, China, and Russia.
Causes of Hail
Severe storms develop in cumulonimbus clouds. This type of cloud forms tall, tower-like shapes that go high into the atmosphere. Cumulonimbus clouds can intensify into supercells, which produce severe thunderstorms. A supercell can produce hail, along with lightning, tornadoes, and high winds.Severe weather occurs when the atmosphere is unstable.
When air is moving up through the cloud (updraft) or down through the cloud (downdraft), it can cause all types of precipitation and weather events to occur. Thunderstorms typically form over areas of the ground that have been heated by the sun in the late afternoon and early evening hours when the temperature is the warmest. Updrafts form and carry the warm air in an upwards direction. Since cumulonimbus clouds are so high, they contain ice crystals and cool temperatures at higher elevations. During a severe storm, updrafts carry raindrops higher into the atmosphere where the temperatures are very cold. When the raindrops enter the cold part of the atmosphere, they freeze into balls of ice. The ice balls are carried in the updraft and grow in size.
When the updraft weakens, or the ice ball is too heavy, the ice falls down towards the ground as hail.
Formation of Hail
Hail forms as rain droplets, move higher in a cloud, and freeze in very cold temperatures. The balls of ice move along with the updraft higher in the cloud. They come in contact with supercooled water, which freezes on contact with any particle, such as ice crystals, raindrops, dust, or some other type of particle.Hail forms in layers as it moves back and forth in the cloud in the updraft, causing some hail stones to look like onions. Other hail stones have odd shapes if they melted in a warmer area of air and then froze again when moved into cooler temperatures.
Hail is a type of precipitation in the form of ice balls that fall to the ground. They occur within severe storms during which begin as cumulonimbus clouds tall, tower-shaped clouds that go high into the atmosphere and then turn into supercells, which ultimately produce thunderstorms. A hailstone’s diameter actually determines whether a storm is severe or not.During a severe thunderstorm, updrafts of warm air carry raindrops high into the atmosphere.
The raindrops freeze into balls of ice, and then move higher into the colder temperatures. Hailstones get larger in size as droplets of supercooled water freezes on contact with any type of dust, ice crystal, or other small particle. Hail falls back to the ground when the balls of ice become too heavy to move higher or when the updraft weakens. When hail falls during a severe storm, it causes damage.