A strong updraft can keep a developing hailstone suspended within a thunderstorm for an extended period.
During that time, the hailstone can collide with additional droplets, collect more ice, and increase in mass.
However, the relationship between updraft strength and hailstone size is not perfectly straightforward. The storm's internal structure, the movement of ice particles, and the availability of liquid water also influence how large the hail becomes.
Eventually, even a powerful updraft cannot support an indefinitely growing ice particle.
When the hailstone becomes too heavy or moves into a weaker region of the storm, it begins falling toward the ground.
Large hailstones can cause significant damage because their mass and falling speed allow them to transfer substantial energy on impact.
A small hailstone may bounce harmlessly off a roof or pavement. A much larger one can crack roof tiles, break windows, dent metal surfaces, damage vehicles, and injure people or animals.
This is why meteorologists pay particular attention to storms capable of producing large hail rather than considering every hailstorm equally dangerous.
The Role of Powerful Updrafts
Updrafts are central to understanding how hail develops.
During an unstable weather situation, warm and moist air near the surface may rise rapidly into cooler air above it. As the rising air expands and cools, water vapor condenses into cloud droplets, helping form towering thunderclouds.
If atmospheric conditions support strong vertical motion, the cloud may develop powerful updrafts.
Inside these clouds, water droplets, ice crystals, and partially frozen particles can circulate through different temperature zones.
A developing hailstone may travel through regions containing supercooled water, collecting additional layers of ice as it moves.
Some hailstones develop irregular shapes because their growth is influenced by the amount of water they encounter, their rotation, and the conditions under which that water freezes.
Others may appear relatively rounded when photographed after landing.
The internal structure of a hailstone can sometimes reveal information about its development. When a hailstone is cut open, it may display alternating translucent and opaque layers.
These layers can form under different growth conditions. Relatively clear ice may develop when water freezes more slowly, allowing air bubbles to escape, while opaque ice can form when freezing occurs more rapidly and traps more air.
However, the layers are not a perfect record of the hailstone's journey, and interpreting them requires an understanding of the storm environment.
The key point is that hail is not simply rain that freezes while falling through cold air. Its growth usually occurs within the storm cloud before the ice reaches the ground.
Why Does Hail Sometimes Cover the Ground Like Snow?
A lawn or field covered in hailstones can look remarkably similar to a winter landscape.
The difference is that hail accumulation can happen during a thunderstorm when the surrounding air and ground are much warmer than they would be during snowfall.
Several factors determine whether hail accumulates.
First, the intensity of the hailfall matters. If hundreds or thousands of stones land within a short period, they may cover the ground faster than they can melt.
Second, the size of the hailstones influences how long they remain intact. Larger pieces of ice generally require more heat to melt completely than smaller ones of comparable material.
Third, the surface temperature plays an important role. Grass, soil, roads, and roofs may have different temperatures and thermal properties, affecting how quickly ice melts after landing.
Finally, rain and drainage conditions can influence where the hail collects. Low-lying areas, gutters, roadside channels, and garden depressions may accumulate ice or a mixture of ice and water.
A dense layer of hail can temporarily make roads slippery and obstruct drainage systems.
In extreme cases, large accumulations may damage vegetation or place additional strain on vulnerable structures. Hail that collects in gutters can contribute to drainage problems, while ice mixed with heavy rain may create localized flooding.
The photographs of a hail-covered lawn illustrate how dramatically a storm can change the appearance of an outdoor space.
However, the amount of hail visible in an image does not by itself establish the storm's total accumulation, duration, or severity across the surrounding area.
Those details would require reliable observations, measurements, or meteorological reports.
Is Giant Hail Becoming More Common?
Questions about severe weather frequently lead to concerns about climate change.
Scientists have documented changes in many aspects of the global climate, including rising average temperatures, increasing atmospheric moisture in some regions, and changes in the frequency or intensity of certain types of extreme precipitation.
However, hail is particularly challenging to study because it varies greatly over short distances and can be difficult to measure accurately.
A severe hailstorm may affect one town while a nearby community experiences only heavy rain.
Small hailstones may melt before anyone records them, while large stones can be collected and measured after a storm. Reports also depend on population density, access to weather stations, radar coverage, and the availability of eyewitness observations.
Research on how climate change affects hail therefore involves several interacting factors.