When the estimated hail is less than 2 inches, it can be as large as a pea to a golf ball. While hail of any size can damage your vehicle, hail at least one inch in diameter can cause serious damage.
Individual hailstones can grow to be as large as 6 inches in diameter. Moreover, hailstones can clump together in the clouds and become even larger. These aggregates can become so large they may be able to kill a person they fall on, but this is highly unlikely. As a rule, intense storms produce larger hail.
Hailstones 1.5 inches in diameter or larger can easily damage windows, especially causing damage that can allow moisture and air to enter through cracked glass or broken seals. Quarter inch (1 inch) hail can damage roof tiles, golf ball sized hail (1.75 inches) can dent a car, and golf ball sized hail can damage tennis (2.5 inches) or more. break car windows and destroy crops. While hail less than an inch in size can damage your car if it is blown in the wind or is very dense, hail less than an inch in size is unlikely to damage your car.
Rain Predominates When Hail Falls
Although large hail can be extremely destructive, the mass of water in hail is typically only 2-3% of the mass of rain during the same storm. The rate at which hail falls is mainly dependent on the size of the hailstone, the friction between the hailstone and the surrounding air, local wind conditions (both horizontal and vertical), and the melting rate of the hailstone. Hail falls when the updraft of a thunderstorm can no longer support the weight of the hailstone, which can happen if the rock gets large enough or the updraft weakens.
Smaller hailstones can be blown away by the updraft of a thunderstorm from the horizontal wind, so larger hailstones usually fall closer to the updraft than smaller hailstones. When the updraft thunderstorm speeds are high enough (greater than 35 m/s) and the hailstones are still small enough, some of the hailstones can be ejected from the updraft, depriving them of much further growth (because they are no longer suspended in the updraft).
In such a scenario, the suspended hailstones greedily absorb the supercooled droplets, reaching up to four inches in diameter (the size of a softball) when the updraft velocity is very high (50 meters per second or higher).
How Hail Forms During Thunderstorms
As the frozen water drops begin to fall, if the updraft speed is high enough, the hailstone rises and more water freezes around it. Whenever ice balls or small hailstones are pushed into the cold upper layers, they collide with drops of supercooled water that freeze onto the growing hailstones. Due to the constant re-freezing of hailstones as they are being weighed during a storm, it is common to see layers of ice in the hailstone.
Hailstones can have transparent cloud layers of ice if the hailstone falls into different temperature conditions and liquid water content during a storm. At very high altitudes, the air is cold enough (below -40 degrees Fahrenheit) that all liquid water will turn into ice, and hailstones need liquid water to grow to any noticeable size. When the hailstone hits supercooled water drops, the drop instantly freezes on the hailstone, allowing the hailstone to expand in size.
The hailstone will then begin to fall, picking up more raindrops as it descends, until it meets those updrafts again and rises into the sky, freezing this newly received water into another layer of ice.
The process will be repeated and the hailstone will continue to grow in size until it becomes heavier than the updraft can support, at which point it will fall to the ground. The hailstones may begin to melt and then freeze together again, forming a large, very irregular hailstone. Hail falls when it becomes heavy enough to overcome the force of the updraft and is pulled towards the ground by gravity.
While for the most part hail is just a nuisance, during severe storms hail can grow to several inches, damage homes and vehicles, and can even be fatal to people and livestock. Hail is one of the biggest hazards in heavy thunderstorms: although it is usually small and relatively harmless, it can grow to the size of a tennis ball or even more. He cites research showing that the hail you normally see during a severe thunderstorm falls at about 25 to 40 miles per hour.
Stronger Storms Produce Larger Hailstones
Hail size can vary greatly from one storm to the next depending on the strength of the storms’ updraft. As you may remember, hail over two inches in size occurs almost exclusively during supercell thunderstorms, and on rare occasions supercells can cause giant hailstones.
In more powerful supercells, which produce the largest hailstones one would expect (2 inches to 4 inches in diameter), predicted fall speeds are between 44 and 72 miles per hour. Very large hail stones, such as baseball hail, can fall at about 100 miles per hour, causing windows to explode and cause a lot of damage. It is clear that a hailstone with a diameter of 30 mm falling in a strong wind has a greater potential for damage than a stone of the same size falling in a light wind (or even an updraft).
In order for the hail to get big enough to reach the surface, the rock must get big enough during the storm before it can fall into the warm lower atmosphere. According to the National Oceanic and Atmospheric Administration (NOAA), the speed at which hailstones fall depends on the size of the hailstone and the surrounding air and wind. If hail falls where the ground is covered, it can cause icy and slippery roads, even in the middle of summer.
If the storm is strong enough, hail can cause cracks in the windshield or side mirrors, or even shatter windows and taillights. Hail can cause concussion or life-threatening head injury to humans and animals if the hail is large enough. The pieces of hail in the hail lanes were so deep that a snowplow was needed to remove them, and hailstones were occasionally reported. Hail is usually the size of a pea or marble, but severe thunderstorms can produce large hailstones.