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How does hail form?

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Quick answer

Hail forms in thunderstorms when updrafts lift raindrops into freezing air, turning them into ice. These ice pellets grow by collecting supercooled water, which freezes in layers. Once too heavy for the updraft, they fall as hailstones, ranging from pea-sized to softball-sized.

Hail forms when strong updrafts in thunderstorms carry raindrops high into freezing air, where they freeze into ice pellets. These pellets grow larger as they collide with supercooled water droplets, eventually falling when they become too heavy for the updraft to support.

Step by step

  1. A strong thunderstorm updraft carries water droplets upward into air colder than 0°C.
  2. The droplets freeze into small ice particles, which serve as the cores of hailstones.
  3. Supercooled water droplets in the cloud collide with these ice cores and freeze onto them.
  4. The updraft keeps the growing hailstones aloft, allowing multiple layers of ice to accumulate.
  5. When the hailstone becomes too heavy for the updraft, it falls toward the ground.
  6. During its fall, the hailstone may partially melt if it passes through warm air near the surface.

Key things to understand

  1. Hailstones begin as small ice particles in the cold upper regions of cumulonimbus clouds.
  2. Supercooled water droplets, which remain liquid below 0°C, freeze onto these particles when they collide.
  3. The stronger the updraft, the longer the hailstone stays aloft and the more layers of ice it accumulates.
  4. Each trip through the cloud adds a new layer, creating concentric rings visible when the hailstone is cut open.
  5. When the hailstone becomes too heavy for the updraft, it falls to the ground, melting partially if the air below is warm.

Labelled diagram

  1. Updraft

    Strong rising air carries water droplets upward into freezing temperatures.

  2. Freezing Level

    Altitude where air temperature drops below 0°C, causing droplets to freeze.

  3. Ice Core

    Initial frozen droplet that becomes the center of a hailstone.

  4. Supercooled Water

    Liquid water below 0°C that freezes onto the ice core upon contact.

  5. Layered Growth

    Repeated collisions add concentric ice layers as the hailstone circulates.

  6. Fall

    Hailstone becomes too heavy for updraft and falls to the ground.

Hailstone Formation in a Thunderstorm

Real-world examples

  • In the United States, the Great Plains region experiences frequent hailstorms, often called 'Hail Alley'.
  • A 2018 hailstorm in Colorado produced hailstones larger than baseballs, causing significant damage.
  • In India, hailstorms in the northern plains during pre-monsoon season can destroy standing crops.
  • The world's largest recorded hailstone fell in Vivian, South Dakota, in 2010, measuring 8 inches in diameter.

Common mistake

✗ Myth: Hail forms only in winter because it is ice.

✓ Fact: Hail actually forms most often in summer, when thunderstorms are frequent and strong updrafts can carry water high into freezing air. The ice then falls through warm air, but large hailstones may not melt completely before reaching the ground.

People also ask

What causes hail?
Hail is caused by strong updrafts in thunderstorms that lift raindrops into freezing air, where they turn into ice. These ice particles grow by collecting supercooled water droplets, which freeze on contact. When the hailstones become too heavy for the updraft, they fall to the ground.
Why is hail sometimes so big?
Hailstone size depends on the strength of the updraft and the amount of supercooled water available. A stronger updraft keeps hailstones aloft longer, allowing more layers of ice to accumulate. The largest hailstones form in severe thunderstorms with very powerful updrafts that can exceed 100 mph.
How fast does hail fall?
Hail falls at speeds ranging from about 9 mph for small pea-sized stones to over 100 mph for large ones. The exact speed depends on the hailstone's size, shape, and the air resistance it encounters. Large hailstones can cause significant damage due to their high impact speed.
Why does hail fall in summer?
Hail forms in thunderstorms, which are most common in warm seasons because heat and humidity fuel strong updrafts. The freezing level in the atmosphere is still high enough for ice to form, and the hot ground does not melt large hailstones completely before they land.
How big can hailstones get?
Hailstones can grow to the size of golf balls, baseballs, or even grapefruits in extreme storms. The largest ever recorded in the United States was about 8 inches in diameter, but most hailstones are pea- to marble-sized.
What is the difference between hail, sleet, and snow?
Hail is chunks of ice that form in thunderstorms and fall as solid ice. Sleet is small ice pellets that form when snow melts and refreezes before hitting the ground. Snow is frozen water vapor that falls as ice crystals without melting.
Can hail predict severe weather?
Large hail often indicates a severe thunderstorm with strong updrafts, which can also produce damaging winds and tornadoes. Meteorologists watch hail size and radar signatures to issue warnings, but hail alone does not guarantee a tornado.

Part of the guide: Water & Weather Phenomena →