why does hailstones have layers?

The Deep Dive

The fascinating layered structure of hailstones is a direct result of their turbulent journey within the powerful updrafts and downdrafts of a cumulonimbus cloud, commonly known as a thunderhead. A hailstone begins as a tiny ice crystal or a frozen raindrop high in the cloud. Strong updrafts lift this embryo, where it collides with supercooled water droplets, which are liquid water existing below freezing point. These droplets freeze onto the hailstone's surface. As the hailstone grows, its weight eventually overcomes the updraft, and it begins to fall. However, it can be caught again by another strong updraft, propelling it back into the colder upper regions of the cloud. This cycle of rising and falling exposes the hailstone to different environmental conditions. When it passes through regions with abundant supercooled water and temperatures just below freezing, the water freezes slowly, allowing trapped air to escape, forming a layer of clear ice. Conversely, when it passes through colder, drier regions or where freezing is rapid, many tiny air bubbles become trapped, resulting in a milky or opaque ice layer. The alternating conditions of wet and dry, warm and cold within the storm create these characteristic concentric layers, much like the rings of an onion, each telling a story of its growth and trajectory through the storm's core until it finally becomes too heavy and falls to the ground.

Why It Matters

Understanding why hailstones have layers is crucial for meteorologists to gain insights into the internal dynamics of severe thunderstorms. By analyzing the number, thickness, and composition of these layers, scientists can reconstruct the updraft strength, water content, and temperature profiles within the storm that produced the hail. This information helps improve forecasting models for severe weather events, enhancing our ability to predict hail size and intensity, which is vital for public safety, aviation, and agriculture. Knowing the conditions that create large, destructive hailstones allows for better warnings and mitigation strategies, protecting crops, property, and lives from significant damage.

Common Misconceptions

A common misconception is that each distinct layer in a hailstone represents a single trip up and down within the thunderstorm. While hailstones do cycle through updrafts and downdrafts, the layers are more precisely a record of varying accretion rates and freezing conditions, not necessarily discrete loops. A single journey might produce multiple layers if it passes through different microclimates within the cloud. Another misunderstanding is that all hailstones are perfectly spherical and exhibit clear, numerous layers. In reality, hailstones come in various irregular shapes, and some may have only a few, less distinct layers, depending on the complexity and duration of their growth within the storm.

Fun Facts

• The largest hailstone ever officially recorded in the United States fell in Vivian, South Dakota, in 2010, measuring 8 inches in diameter and weighing nearly 2 pounds.
• Hailstones can reach terminal velocities of over 100 miles per hour as they fall, posing significant hazards to aircraft and ground infrastructure.