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Hail: the story on HearLore | HearLore
Hail
On the 14th of April 1986, a single hailstone weighing 1.02 kilograms struck the Gopalganj District in Bangladesh, killing 92 people and leaving a legacy of terror that persists in local memory. This event, along with the 1888 hailstorm in Moradabad that claimed over 200 lives, illustrates that hail is not merely a weather curiosity but a lethal force capable of ending human life. While modern records show that fatalities in the United States are rare, with only three deaths recorded since the inception of modern tracking, the historical toll has been catastrophic. In the 9th century, researchers have even suggested that a hailstorm caused the deaths of several hundred nomads in Roopkund, Uttarakhand, India, though this theory remains disputed. The sheer violence of these events stems from the fact that hailstones can fall at terminal velocities exceeding 100 miles per hour, turning them into projectiles capable of shattering windshields, crushing roofs, and inflicting fatal head trauma on those caught without shelter. The 1926 hailstorm in Dallas, Texas, which produced stones as large as 4.5 inches, serves as a grim reminder of the destructive power inherent in these frozen masses, causing billions of dollars in damage to automobiles and infrastructure that still echoes through insurance records today.
The Anatomy Of A Storm
The formation of a hailstone is a complex journey through the violent heart of a cumulonimbus cloud, requiring a specific set of atmospheric conditions to transform a simple water droplet into a layered sphere of ice. Hail begins as water droplets that rise into the freezing zone of a thunderstorm, where they become supercooled and freeze upon contact with condensation nuclei. As the storm's updraft, which can reach speeds of 100 miles per hour, blows the forming hailstone upward, it passes through varying zones of humidity and supercooled water droplets. This process creates an onion-like structure within the stone, characterized by alternating layers of thick translucent ice and thin opaque white ice. The translucent layers form when the hailstone captures a high concentration of water droplets, while the opaque layers result from rapid freezing that traps small air bubbles, a process known as dry growth. Unlike older theories that suggested multiple descents and ascents were necessary to create these layers, modern research indicates that a unique trajectory through the cloud is sufficient to explain the structure. The stone continues to grow and release latent heat, keeping its exterior in a liquid phase during wet growth, allowing it to collide with other smaller stones and form irregular, clumped entities. This cycle continues until the mass of the hailstone becomes too great for the updraft to support, at which point it falls to the ground, often melting as it passes through warmer air but retaining its layered history.
Common questions
What happened during the 1986 hailstorm in Gopalganj District Bangladesh?
On the 14th of April 1986, a single hailstone weighing 1.02 kilograms struck the Gopalganj District in Bangladesh, killing 92 people and leaving a legacy of terror that persists in local memory.
How do hailstones form inside cumulonimbus clouds?
Hail begins as water droplets that rise into the freezing zone of a thunderstorm, where they become supercooled and freeze upon contact with condensation nuclei. The storm's updraft blows the forming hailstone upward through varying zones of humidity and supercooled water droplets, creating an onion-like structure with alternating layers of thick translucent ice and thin opaque white ice.
Where are the most frequent hailstorms located globally?
Hail is most common within continental interiors of the mid-latitudes, particularly in regions where mountains force horizontal winds upwards. Key hotspots include Hail Alley in North America, the Hailstorm Alley region of Alberta, central Argentina, and Kericho Kenya, which experiences hailstorms on average 50 days annually.
How do meteorologists detect hail before it strikes the ground?
Modern radar scans many angles around a site to calculate the Vertically Integrated Liquid or VIL, which provides a relationship with hail size. A specific pattern known as the three-body scatter spike serves as a crucial clue, resulting from radar energy hitting hail and being deflected to the ground, then back to the hail, and finally to the radar.
What is the economic impact of hail on the United States in 2023?
Hailstorms cost the United States $46 billion in damage to cars, roofs, and crops in 2023 alone, according to the Insurance Institute for Business & Home Safety. Hail is one of the most significant thunderstorm hazards to aircraft and causes severe damage to automobiles, roofs, and crops such as wheat, corn, soybeans, and tobacco.
Have cloud seeding programs successfully reduced hail damage?
Updated versions of cloud seeding programs using silver iodide have been undertaken by 15 countries between 1965 and 2005 with mixed results. While the Soviet Union claimed a 70 to 98 percent reduction in crop damage, these effects have not been replicated in randomized trials conducted in the West.
While thunderstorms are common in the tropics, hail is surprisingly rare there because the atmosphere remains warm over a much greater altitude, preventing the necessary freezing levels from forming. Instead, hail is most common within continental interiors of the mid-latitudes, particularly in regions where mountains force horizontal winds upwards, a phenomenon known as orographic lifting. This intensifies the updrafts within thunderstorms, making hail more likely and allowing stones to grow larger before falling. In North America, the area where Colorado, Nebraska, and Wyoming meet is known as Hail Alley, with Cheyenne, Wyoming, being the most hail-prone city, experiencing an average of nine to ten hailstorms per season. To the north, the Hailstorm Alley region of Alberta also sees significant events. In South America, the central region of Argentina, extending from Mendoza to Córdoba, experiences some of the most frequent hailstorms in the world, with 10 to 30 storms per year on average. The Patagonia region of southern Argentina and the triple border region between Brazil, Argentina, and Uruguay are also hotspots. In Europe, southern and western Germany, northern and eastern France, and southern and eastern Benelux regions register high frequencies of hail. One of the most extreme locations is Kericho, Kenya, which is close to the equator but benefits from an elevation of 2,200 meters, allowing it to experience hailstorms on average 50 days annually and even reaching a record of 132 days of hail in a single year. These regions demonstrate that the combination of elevation, moisture transport, and atmospheric instability creates the perfect environment for hail to thrive.
The Science Of Detection
Detecting hail before it strikes the ground requires a sophisticated understanding of weather radar and atmospheric data, as traditional methods often fail to predict the exact size and location of the stones. Modern radar scans many angles around a site, and reflectivity values at multiple angles are proportional to the precipitation rate, allowing meteorologists to calculate the Vertically Integrated Liquid or VIL. This data, when divided by the vertical extent of the storm to determine VIL density, provides a relationship with hail size, although the accuracy varies with atmospheric conditions. A specific pattern known as the three-body scatter spike serves as a crucial clue, resulting from radar energy hitting hail and being deflected to the ground, then back to the hail, and finally to the radar, creating a cone of weaker reflectivities that indicates the presence of hail inside the storm. Since 2025, scientists in the United States have engaged in the In-situ Collaborative Experiment for Collection of Hail In the Plains, or ICECHIP, which is the world's largest field campaign devoted to studying hail. This project involves 100 scientists from four countries and 11 states, focusing on two areas known as hail alleys: the Great Plains and the Front Range of the Rocky Mountains in Colorado and Wyoming. The goal is to shed light on unanswered questions about hail formation and growth, using data from radar, lightning, and synoptic weather patterns to predict these events before they occur. Despite these advancements, false alarm rates remain high, and the lack of data on hail depth continues to leave researchers and forecasters in the dark when trying to verify operational methods.
The Cost Of Ice
The economic impact of hail is staggering, with hailstorms costing the United States $46 billion in damage to cars, roofs, and crops in 2023 alone, according to the Insurance Institute for Business & Home Safety. Hail is one of the most significant thunderstorm hazards to aircraft, capable of seriously damaging planes within seconds if stones exceed 1 inch in diameter. On the ground, hail causes severe damage to automobiles, denting vehicles and shattering windshields, while roofs, particularly shingled and flat ones, often suffer hidden structural damage that goes unnoticed until leaks or cracks appear. Metal roofs are relatively resistant but may accumulate cosmetic damage in the form of dents and damaged coatings. Crops such as wheat, corn, soybeans, and tobacco are highly sensitive to hail damage, making agriculture one of the most vulnerable sectors. In Canada, hail is one of the most expensive hazards, and in the United States, despite billions of dollars in damage and the common occurrence of large hail, only three people have been known to be struck and killed by hail since modern records have been kept. The 2010 hailstorm in Boulder County, Colorado, which produced a foot of hail accumulation, and the 2015 event in Denver, where hail up to four feet deep fell on a single city block, highlight the potential for massive accumulation. These events can cause thousands to lose power, bring down trees, and lead to flash flooding and mudslides, turning the landscape into a slushy mess that requires tractors and dump trucks to clear.
The Battle Against The Sky
Throughout history, humanity has attempted to control the sky, from the Middle Ages when people in Europe rang church bells and fired cannons to prevent hail, to modern cloud seeding programs that use silver iodide to reduce crop damage. Updated versions of these approaches exist as modern hail cannons, and cloud seeding after World War II was done to attempt to eliminate the hail threat, particularly across the Soviet Union, where it was claimed that a 70 to 98 percent reduction in crop damage was achieved by deploying silver iodide in clouds using rockets and artillery shells. However, these effects have not been replicated in randomized trials conducted in the West, and hail suppression programs have been undertaken by 15 countries between 1965 and 2005 with mixed results. The challenge lies in the complexity of the atmosphere, where the interaction of updrafts, freezing levels, and moisture creates a dynamic system that is difficult to manipulate. Despite the lack of proven success in large-scale suppression, the effort continues, with researchers and forecasters working to develop better methods to predict and mitigate the impact of hail. The 2010 and 2015 events in Colorado, which required tractors to clear over 30 dump truck loads of hail, underscore the need for effective prevention strategies. The joint project between the University of Colorado and the National Weather Service aims to enlist the help of the general public to develop a database of hail accumulation depths, hoping to improve the ability to predict and prepare for these events. The battle against the sky remains ongoing, with scientists striving to understand the intricate processes that govern hail formation and growth.