Hailing occurs when powerful thunderstorm updrafts loft water droplets into sub-freezing altitudes, where they accumulate layers of ice and eventually fall as solid chunks that can range from pea-sized pellets to softball-sized projectiles. The process demands a specific atmospheric recipe, and the stones themselves carry a hidden record of their journey through the storm. Much remains poorly understood about hail outside the United States and Europe, and what we do know continues to shift as climate change alters the balance of forces that govern hailstone size and frequency.
How a Hailstone Grows
Every hailstone starts as an embryo, a small particle of ice or frozen water around which additional layers can accumulate. The embryo is swept upward by a thunderstorm’s updraft, and as it rises through colder regions of the cloud it collects supercooled water droplets that freeze on contact. This growth phase can happen in two modes. In “dry growth,” the stone is cold enough that droplets freeze almost instantly, trapping tiny air bubbles that give the ice a milky, opaque appearance. In “wet growth,” the surface of the stone is warm enough that water doesn’t freeze immediately, spreads across the surface, and eventually freezes as a clearer, denser layer. A single hailstone often cycles between these two modes, which is why cutting one open reveals alternating rings of clear and opaque ice, much like tree rings.
Recent isotopic work has confirmed this picture in striking detail. Researchers in Texas sliced hailstones from two supercell events and measured hydrogen and oxygen isotopes at half-centimeter intervals from core to surface. Because the ratio of heavy to light hydrogen shifts with altitude, each layer effectively records how high the stone was when it formed. The results showed significant variation from layer to layer, confirming that individual hailstones are recycled through different altitudes in the updraft rather than growing in a single, smooth ascent.1Journal of Geophysical Research: Atmospheres. Tracing Hailstone Development: Isotopic Evidence and Microphysical Variability in Texas Supercell Events
A complementary study analyzed the chemical composition of hailstone layers, measuring eight water-soluble ions along with stable isotopes of water. The ion concentrations followed a distinctive V-shaped pattern: highest near the innermost core, dropping in the intermediate layers, and climbing again near the outer surface. This pattern reflects the stone’s passage through regions with different aerosol concentrations, essentially fingerprinting the storm environment at each stage of the stone’s life.2Science Bulletin. Chemical composition of a hailstone: evidence for tracking hailstone trajectory in deep convection
Bacteria That Help Start the Process
One of the more surprising discoveries in hail science is that biological particles, particularly certain bacteria, play a meaningful role in getting hailstone embryos started. Ice doesn’t form spontaneously in the atmosphere just because the temperature drops below freezing. It needs a surface to crystallize on, called an ice nucleus. Most people assume those nuclei are mineral dust or soot, and those particles do contribute. But research on hailstone embryos collected from Rocky Mountain storms found that biological ice nuclei, capable of triggering freezing at relatively warm sub-zero temperatures, were present and likely responsible for catalyzing the initial ice formation. Non-biological particles were also found in the embryos, but at concentrations too low to explain the warm freezing temperatures confirmed by isotope analysis.3Journal of Geophysical Research: Atmospheres. Biological ice nucleation initiates hailstone formation
Among these biological particles, ice-nucleation-active bacteria stand out. These microbes, many of them common plant-surface species, produce proteins on their outer membranes that serve as remarkably efficient ice-forming templates. Quantitative sampling of a thunderstorm hail event found roughly 0.3 ice-nucleation-active bacteria per ice-nucleating particle active at minus 10 degrees Celsius, suggesting that bacteria made a substantial contribution to the ice-nucleating particle population in that sample.4PubMed Central. Measurement of ice nucleation-active bacteria on plants and in precipitation by quantitative PCR The finding connects hail to a broader and still-developing story about how biology influences weather, from the bacteria that help trigger rain to the ones that seed the first ice in a hailstone.
Detecting Hail Before It Hits the Ground
Forecasters rely heavily on dual-polarization radar to identify hail inside active storms. Conventional radar sends out a single horizontal beam and measures the intensity of the signal that bounces back, which tells you something about the size and concentration of particles in the storm. Dual-polarization radar sends both a horizontal and a vertical beam, and the difference in how each beam reflects off a particle reveals the particle’s shape. Raindrops flatten as they fall through air resistance, producing a clear polarization signature. Hailstones, being more spherical or irregularly shaped, produce a different one.
The picture gets more complicated when hailstones are oblate, meaning flattened rather than round. Observations have shown that oblate hail produces nonzero values of differential reflectivity, a quantity that should theoretically be near zero for perfectly spherical stones. This, combined with readings of how the stones depolarize the radar signal, suggests that some hailstones fall with a degree of alignment rather than tumbling randomly.5Quarterly Journal of the Royal Meteorological Society. Observations of oblate hail using dual polarization radar and implications for hail‐detection schemes This matters because many automated hail-detection algorithms assume hailstones tumble, and when stones align instead, the radar signatures can mimic those of heavy rain, causing the algorithm to underestimate or miss the hail entirely. Improving hail-detection schemes remains an active area of research, especially as radar networks expand into regions where hail observations on the ground are sparse.
What Hail Does to Crops, Roofs, and Solar Panels
The economic damage from hail is enormous and touches nearly every sector exposed to the sky. In agriculture, yield losses from severe storms and related short-term weather events typically range from about 5 to 35 percent, though extreme events can wipe out an entire crop.6Crop Science. Severe storm damage and short‐term weather stresses on corn: A review The damage depends on timing: a hailstorm that hits corn early in the season, when the plant’s growing point is still below ground, is far less devastating than one that arrives when ears are developing. Hail shreds leaves, breaks stalks, and strips away the plant’s ability to photosynthesize, and recovery is largely a function of what growth stage was struck and how much tissue survived.
Buildings face their own vulnerability. Asphalt shingles, the most common residential roofing material in much of the world, degrade under repeated hail strikes as the granular surface coating cracks and the underlying mat loses waterproofing integrity. A single large stone can punch through aged shingles entirely. The insurance industry has responded by developing impact-resistance rating systems, but homeowners often don’t realize that shingles meeting the highest rated class still have size limits beyond which they fail.
A growing concern involves damage to photovoltaic solar panels, which are inherently exposed and increasingly widespread. Large hail causes billions in economic losses annually through damage to crops and property worldwide, and the specific risk to solar installations has become a major area of research interest, with significant damage reports emerging from both Europe and the United States.7Elsevier / Energy Reports. Large hail impacts on photovoltaic systems: A review of damage, testing, and mitigation Solar glass is tempered and tested to withstand stones up to about 25 millimeters in diameter at typical terminal velocities, but larger hailstones exceed that design threshold. Cracked glass allows moisture into the photovoltaic cells, causing progressive electrical degradation that may not be immediately visible. For large solar farms in hail-prone corridors, this is becoming a real financial liability.
Modeling the Costs
Insurance companies have an obvious interest in predicting where hail will strike and how much damage it will cause, but the spatial patterns of hail damage are notoriously erratic. A storm can demolish every roof on one side of a street and leave the other side untouched, because hailstones within a single event vary widely in size and fall in swaths rather than blanketing an area evenly. Traditional insurance models relied on deterministic hail-impact functions, essentially formulas that estimate damage based on estimated hailstone energy. But these models struggle with the localized, extreme damage patterns that real hail events produce.
Newer Bayesian approaches that model both the geographical footprint of a hailstorm and the damage caused by individual stones have shown improvement. One such model, built from hail-related insurance claims, uses a spatial framework that accounts for how damage clusters along narrow corridors and allows for localized extreme values. This model outperformed the benchmark deterministic approach at capturing both the spatial patterns of claims and the magnitude of extreme damage.8Project Euclid. Bayesian modeling of insurance claims for hail damage For homeowners, the practical takeaway is that hail damage risk is highly local and can’t be easily averaged over a city or county. Two houses a few hundred meters apart may face very different long-term risk depending on their precise position relative to common storm tracks.
How Climate Change Is Reshaping Hail
The relationship between a warming climate and hail is not simply “more heat, more storms.” Instead, two competing forces are pulling hailstone sizes in opposite directions. A warmer atmosphere holds more moisture and generates greater instability, which fuels stronger updrafts. Stronger updrafts can support larger stones for longer before gravity wins, meaning the biggest hailstones get even bigger. At the same time, warmer surface temperatures push the freezing level higher in the atmosphere, creating a thicker layer of above-freezing air that hailstones must fall through before reaching the ground. Smaller stones melt significantly in this thicker warm layer; many that would have reached the surface as hail in a cooler climate will instead arrive as rain.
The result is a size dichotomy. Research modeling future hailstone distributions found that stronger updrafts in warmer environments promote more of the largest hailstones, while a significant decrease occurs for the majority of smaller diameters due to increased melting.9npj Climate and Atmospheric Science. Hailstone size dichotomy in a warming climate In practical terms, this could mean fewer total hail events but more frequent encounters with the most damaging, large-diameter stones. If you live in a hail-prone area, the risk profile may be shifting from frequent minor pelting to less frequent but more severe impacts, exactly the kind of shift that makes insurance modeling more difficult and building codes more important.
The observational picture outside North America and parts of Europe is thin enough to make global trend statements unreliable. Much remains unknown about the environmental controls on hail occurrence, size, and frequency in regions where surface observation networks are sparse and radar coverage is limited.10Reviews of Geophysics. Understanding Hail in the Earth System Countries in central Asia, sub-Saharan Africa, and much of South America almost certainly experience significant hail, but the data needed to characterize trends simply doesn’t exist yet.
Trying to Stop Hail With Silver Iodide
For decades, people have tried to suppress hail by seeding storms with silver iodide, a compound whose crystal structure mimics ice and promotes the formation of many small ice particles rather than fewer large ones. The theory is straightforward: if you give a storm thousands of extra ice nuclei, the available supercooled water spreads across more embryos, and none of them grow into the large, destructive stones that cause the worst damage. Instead, you get lots of small pellets or even graupel that melts before reaching the ground.
The evidence for this approach is mixed but not zero. Results compiled from hail suppression projects conducted around the world over roughly three decades suggest that silver iodide seeding suppresses hail in some storms but not in others, and the seeding effect is largely independent of the amount of silver iodide used, provided some reasonable threshold is exceeded.11The Journal of Weather Modification. How Silver Iodide seeding suppresses hail This is an important and somewhat counterintuitive finding. Dumping more silver iodide into a storm doesn’t reliably produce a bigger suppression effect. Once you’ve crossed a certain seeding level, additional material doesn’t help. And some storm structures appear resistant to the technique entirely.
The strongest positive results come from ground-based seeding networks in France and Spain. Analysis of both historical and modern field projects in those countries concluded that if ground seeding with a network of generators spaced about 10 kilometers apart begins roughly three hours before hail reaches the surface, the hailfall energy of the most severe hail days can be reduced by about half.12Atmospheric Research. Hail prevention by ground-based silver iodide generators: Results of historical and modern field projects That is a meaningful reduction for the worst events, though it falls well short of full prevention and requires infrastructure that not every region has invested in.
It’s worth noting the gap between the operational programs that continue in parts of Europe and the scientific consensus, which remains cautious. The challenge is that hailstorms are inherently variable, and without a controlled experiment (you can’t seed half a storm and leave the other half untouched in any precise way), it is difficult to prove that the seeding caused the observed reduction rather than natural variability. Countries like the United States have largely moved away from operational hail suppression programs, while others, including Argentina, China, and several European nations, maintain them.
Hail Cannons and Other Unconventional Approaches
Hail cannons, devices that fire shock waves upward into approaching storms, have been used by farmers and vineyard owners since the late 1800s. The idea is that repeated concussions disrupt the formation of hailstones, either by shattering embryos or by preventing the organized updraft structures that sustain large stone growth. For most of their history, hail cannons had essentially no scientific support. They were regarded as folklore by atmospheric scientists, and the few observational studies that existed found no detectable effect.
That picture shifted slightly with recent computational work. Three-dimensional simulations of a hail cannon’s shock wave propagation into cloud-scale moisture fields found that a sustained sequence of shock waves over an extended period could significantly reduce cloud vapor in the simulated environment. The researchers described their results as the first simulational verification of the hail cannon concept.13Lecture Notes in Computer Science. The First Scientiffic Evidence for the Hail Cannon “Verification” here is a strong word for what amounts to a numerical modeling exercise rather than a field trial, and the gap between reducing vapor in a simulation and preventing real hailstones from forming in a chaotic thunderstorm environment is enormous. Still, the work represents a first attempt to apply physics-based modeling to a device that had previously been dismissed out of hand. Whether hail cannons have any real-world effect remains an open question, but at minimum, someone has now bothered to check the math.
Engineering Materials to Survive Impact
Rather than trying to prevent hail from forming, much of the practical effort in hail-prone regions focuses on building things that can survive the impact. This is largely a materials science problem, and the stakes keep growing as more high-value infrastructure, from solar farms to composite-clad aircraft, sits exposed to the sky.
One line of research has explored adding nanoclays to the glass-fiber-reinforced epoxy composites used in aerospace and automotive applications. In high-velocity hail impact tests, glass fiber/epoxy panels containing nanoclay produced smaller damage areas and retained higher residual strength compared to panels without it. The nanoclay changed the failure mechanisms during impact, and an addition of about 1.5 percent nanoclay by weight proved optimal for maximizing damage resistance.14Journal of Composite Materials. Hail impact damage behaviors of glass fiber reinforced epoxy filled with nanoclay This kind of incremental improvement matters in applications where even minor damage is expensive to repair, such as aircraft leading edges or wind turbine blades.
For residential roofing, impact-resistant shingles have become common in regions where insurers offer premium discounts for their use. These shingles typically use a polymer-modified asphalt or rubberized backing that absorbs impact energy without cracking. But the testing protocols that certify them fire standardized steel balls at controlled velocities, which doesn’t fully capture the variability of real hail. A 50-millimeter hailstone doesn’t behave like a steel sphere of the same diameter; it shatters on impact, distributing energy differently, and may arrive at speeds and angles that lab testing doesn’t replicate. Some post-storm inspections have found that “impact-resistant” shingles still sustained meaningful damage from large, real-world hailstones, underscoring the limits of any single test protocol.
For solar panels, the most promising mitigation strategies involve either active stowing, where panels are tilted to a steep angle when a hailstorm is forecast so the stones strike a glancing blow rather than a direct hit, or next-generation glass formulations designed to withstand larger-diameter impacts. Active stowing systems require reliable short-term hail forecasts, which loops back to the radar detection challenges described earlier. The whole chain matters: detection accuracy feeds into warning time, warning time feeds into whether automated tilt systems can respond, and tilt-system reliability determines whether the panels survive. Any weakness in that chain leaves the panels exposed.