The Rings Inside a Hailstone Tell the Story of Its Violent Birth

Why Some Layers Are Glass-Clear and Others Look Like Snow

The visual difference between layers comes down to how fast water freezes onto the stone. When a hailstone passes through the wet-growth zone — typically between roughly -10°C and -20°C where supercooled water droplets are abundant — water coats the surface faster than it can freeze. The liquid spreads into a thin film before slowly solidifying. This slow freezing pushes air bubbles out, creating transparent ice that looks like glass.

But when the same stone gets carried higher into the dry-growth zone, typically above approximately -20°C, the physics change completely. Up there, water droplets are smaller and freeze on contact. The freezing happens so fast that air gets trapped between the ice crystals, creating thousands of tiny bubbles that scatter light. That's what makes the opaque, milky-white layers. If you've ever noticed that ice cubes from your freezer are cloudy in the middle but clearer on the edges, you've seen the same principle — fast freezing in the center traps air, while slower freezing at the surface allows bubbles to escape.

According to NSSL hail research, the thickness of each layer depends on how much supercooled water the stone encounters during each pass and how long it spends in each growth zone. A thick clear layer suggests the stone spent extended time in the wet-growth region where water was plentiful. A thin opaque layer might indicate a quick trip through the dry zone before the updraft pulled it back down.

The embryo at the very center — the nucleus that started the whole process — is usually a tiny frozen raindrop or a small ice crystal, though occasionally researchers find a captured insect or a fragment of leaf. Everything else built up around that initial seed through layer after layer of accretion.

Reading the Storm's Biography in Ice

The number of layers reveals something fascinating about the storm's internal structure. A hailstone with just two or three layers likely formed in a relatively weak updraft that couldn't sustain many cycles. But stones with ten or more layers come from exceptionally powerful supercells with updrafts strong enough to repeatedly loft a growing chunk of ice that's gaining weight with every pass.

Research on severe hail production indicates that the most violent supercells — the ones capable of producing baseball-sized or larger hail — can maintain organized updrafts with wind speeds exceeding 100 mph. These updrafts create a kind of conveyor belt system where hailstones get caught in a circulation pattern, rising and falling through different temperature zones in a remarkably consistent rhythm.

The layering pattern also hints at changes in the storm's intensity over time. If the layers become progressively thicker toward the outside, the storm was likely intensifying, providing more supercooled water with each cycle. If the outer layers are thinner, the updraft may have been weakening, giving the stone less time in the wet-growth zone before it fell.

Here's what most people get wrong: they assume a bigger hailstone must have spent more time in the storm. But size depends more on the availability of supercooled water than on time aloft. A stone could make numerous trips through a weak updraft with limited moisture and still end up smaller than a stone that made fewer trips through a moisture-rich supercell. The layers tell you about the number of cycles, but the thickness of those layers tells you about the storm's water content.

Sometimes researchers find asymmetric layering — thicker ice on one side of the stone than the other. This happens when the stone tumbles through the updraft at an angle, exposing different surfaces to different amounts of supercooled water. The lopsided growth can tell you something about wind shear and rotation inside the storm.

The Final Layer Is Always Cloudy

The outermost layer of virtually every hailstone is opaque, and that's not a coincidence. When the stone finally exits the updraft for the last time — either because the updraft collapsed or because the stone became too heavy — it passes through the cold, dry air at the top of the storm or in the surrounding environment. This final passage through extremely cold, dry conditions creates rapid freezing with maximum air entrapment.

That last layer forms quickly, often in just seconds, as the stone begins its final descent to the ground. By the time it lands, the surface has a frosty, white appearance that often masks the glassy layers underneath. If you've ever picked up a fresh hailstone immediately after it fell, you might have noticed this chalky exterior. Let it sit for a few minutes and start to melt, and the clearer inner layers often become visible.

The preservation of these layers depends entirely on keeping the stone frozen. Once melting begins, the boundaries between layers blur and the historical record dissolves. That's why hail researchers who want to study layer structure need to collect stones immediately and store them in freezers. Some of the most detailed hailstone cross-section studies come from storm chasers who carry portable freezers in their vehicles specifically to preserve specimens before the evidence melts away.

Cutting the stone requires patience. Researchers typically use a fine-toothed saw or a heated wire to create a clean cross-section through the center. The goal is to slice through the embryo, revealing the full sequence of layers radiating outward. Under proper lighting, the alternating clear and opaque bands create striking patterns — some stones show perfect concentric rings, while others display irregular, chaotic layering that reflects turbulent conditions inside the parent storm.

The science of reading hailstone layers has practical applications beyond pure curiosity. By analyzing the layer structure of stones from a particular storm, meteorologists can reconstruct details about the storm's updraft strength, moisture content, and vertical temperature profile — information that helps refine forecast models for future severe weather events. Each sliced hailstone is a frozen data recorder, preserving measurements that no weather balloon or radar could capture from inside the most violent part of the storm.