What is Hail?

Hail is a frozen form of precipitation generally associated with severe thunderstorms, especially those which form in advance of cold fronts. Large hailstones is also seen as an early indicator of an approaching tornadic storm cell, and they can cause significant damage to exposed structures and vehicles. There are also documented cases where people have been seriously injured or even killed as a result of a heavy hailstorm.

In order for most examples of hail to form, a number of meteorological conditions need to be in place first. Moisture-laden storm clouds must build up to heights approaching 50,000 feet or more. The air temperature at those heights is cold enough to super freeze water droplets, which means they remain liquid in form but below freezing in temperature. If those super frozen droplets made contact with anything solid, called a nuclei in meteorological terms, they would freeze immediately.

The problem is that there aren't too many solid objects floating around at 50,000 feet above the ground naturally. When the winds inside a storm cloud begin to circulate, a powerful updraft is created. This updraft can pull dust particles, insects or tiny ice crystals up to the cloud's highest levels. When these natural nuclei come in contact with the super frozen droplets, they form a small ball of solid ice. Eventually these new ice formations fall towards the ground, but they could be swept back into the top of the cloud formation over and over again by the updrafts. A new layer of frozen water droplets is added to the young hailstone during each trip.

Eventually the ice droplets become too heavy to be supported by the storm's updrafts. The hailstones then fall to the ground like rain or sleet or snow. The size of an individual stone depends on how many times it was drawn back into the upper levels of the storm cloud before it finally fell. If a large piece of hail were cut in half, there would be a number of layers of ice, much like an onion's layers. Stones may be as small as a pea, or under extreme circumstances could become the size of a softball or even grapefruit.

Not all storm clouds produce hail, since the updrafts may not be strong enough to force nuclei materials into the upper levels or the frozen precipitation may melt before it reaches the ground. A tornadic super cell, on the other hand, can have a very powerful updraft capable of picking up dust particles and other nuclei for hailstones. This is why a strong hailstorm is often an indicator that a tornado is approaching or at least about to form.

Hail is a type of solid precipitation that forms during thunderstorms when updrafts carry raindrops into extremely cold areas of the atmosphere, causing them to freeze. Layers of ice accumulate around the initial frozen core as the hailstone is lifted and dropped within the storm cloud multiple times before falling to the ground.

Hailstones vary in size, from as small as peas to as large as grapefruits. The largest hailstone on record in the U.S. measured nearly 8 inches in diameter and weighed almost 2 pounds, according to the National Oceanic and Atmospheric Administration (NOAA). However, most hailstones are typically less than 2 inches in diameter.

Large hailstones form in strong thunderstorms with intense updrafts, ample moisture, and a large area of the atmosphere below freezing. These conditions allow hailstones to remain suspended in the cloud for longer periods, growing in size as they collide with supercooled water droplets that freeze upon impact, before gravity finally overcomes the updraft and the hail falls to the ground.

While predicting the exact occurrence of hail is challenging, meteorologists can forecast the likelihood of hail by identifying atmospheric conditions conducive to severe thunderstorms. Using radar technology, they can detect areas within a storm that may produce hail and issue warnings to potentially affected regions, as per the National Weather Service.

Hail can cause significant damage to crops, vehicles, buildings, and other property. According to the Insurance Information Institute, hail damage claims in the United States can exceed $1 billion annually. The impact of hail can shatter windows, dent cars, strip vegetation, and compromise the integrity of roofing materials.

To mitigate hail damage, individuals can use protective coverings for vehicles, install hail-resistant roofing, and use shutters or impact-resistant windows. For agriculture, crop covers and anti-hail netting can reduce damage. Awareness of local weather forecasts and having a plan in place during severe weather advisories is also crucial for protection.