why does hailstones have layers in summer?

The Deep Dive

Hailstones are a fascinating product of severe thunderstorms, particularly those with strong updrafts. Imagine a towering cumulonimbus cloud, a churning cauldron of atmospheric energy. Within this cloud, violent updrafts act like a powerful elevator, carrying supercooled water droplets upwards. As these droplets ascend into frigid altitudes, they freeze upon contact with tiny ice particles or other frozen droplets, forming a small hail embryo. This embryo is then repeatedly lifted and dropped by the turbulent air currents within the storm. Each cycle through the cloud allows the hailstone to collect more supercooled water, which freezes onto its surface, adding a new layer of ice. The appearance of these layers, often resembling tree rings, is due to variations in the storm's internal environment. When the hailstone encounters regions with abundant moisture and slightly warmer temperatures (still below freezing), it collects a layer of clear, transparent ice as the water freezes relatively slowly. Conversely, when it moves through drier, colder areas, it accumulates a layer of opaque, milky ice because the water freezes rapidly, trapping air bubbles. The size and number of these layers depend on the hailstone's journey within the storm, dictated by the intensity and duration of the updrafts and downdrafts.

Why It Matters

Understanding hailstone structure helps meteorologists interpret the conditions within thunderstorms. The layering provides clues about the storm's intensity, the altitude at which hail formed, and the amount of supercooled water available. This information is crucial for forecasting severe weather events, including the potential for damaging hail, and for issuing timely warnings to protect lives and property. Analyzing hailstone samples can even help reconstruct past weather events, contributing to climate research and our understanding of atmospheric dynamics.

Common Misconceptions

A common misconception is that hailstones have layers like an onion, with each layer representing a single trip up and down within the storm. While layers do form from repeated cycles, a single hailstone might not complete a perfect up-and-down journey for each layer. Instead, the layers are added as the hailstone is suspended and jostled within different zones of the storm cloud, encountering varying amounts of moisture and temperature. Another myth is that all hailstones are perfectly spherical; in reality, their shape is often irregular, influenced by collisions with other hailstones and the chaotic air currents within the storm.

Fun Facts

• The largest hailstone ever recorded in the United States measured 8 inches in diameter and weighed nearly 2 pounds.
• Hailstones can form in thunderstorms even when the surface temperature is warm, as long as the upper levels of the storm cloud are cold enough.