Storm Systems That Causes Hail

what causes hail? – The Science Behind Hail Formation

Understanding the Conditions and Processes That Create Hailstones

Hail is a remarkable weather phenomenon that occurs during severe thunderstorms, particularly in the states of Nebraska, Colorado, and Wyoming which lie within “Hail Alley.” To fully grasp how hail forms and why certain weather patterns contribute to its creation, let’s explore the science behind this fascinating process.

Key Takeaways

  • Hail forms in storm clouds when ice pieces collide with supercooled water, creating layers and becoming heavier until they fall to the ground.
  • The size of hail is influenced by updraft strength, time spent in the air, and the initial size of the ice pieces.
  • Hail can cause over $1 billion in damage annually to property and crops, and also pose a risk of injury to people. Hail-damaged roof repair accounts for around 40%.

Atmospheric Conditions Necessary for Hail Formation

For hail to form, several atmospheric conditions must be present:

  1. Unstable air: Warm, moist air near the ground rises rapidly, creating an unstable atmosphere.
  2. Strong updrafts: As the warm air rises, it creates powerful updrafts within the thunderstorm cloud.
  3. Cold upper atmosphere: The rising air quickly cools as it reaches higher altitudes, where temperatures are well below freezing.
  4. Supercooled water droplets: At these high altitudes, water droplets remain liquid even though the temperature is below freezing, becoming “supercooled.”

The Hail Formation Process

Hail starts its journey high within storm clouds, where temperatures are below freezing. These conditions are perfect for forming hailstonesUpdrafts in the atmosphere lift water droplets into these cold regions of the cloud, where they freeze and become small ice pellets.

Once the necessary atmospheric conditions are in place, the hail formation process begins:

  1. Ice pellet formation: Supercooled water droplets collide with dust particles or other nuclei in the cold upper regions of the thunderstorm cloud, freezing instantly to form small ice pellets.
  2. Hailstone growth: Strong updrafts carry these ice pellets upward, where they collide with more supercooled water droplets. These droplets freeze upon contact, adding layers of ice to the growing hailstone.
  3. Repeated layering: As the hailstones are repeatedly lifted by updrafts and then fall back down due to gravity, they encounter more supercooled water droplets, creating multiple layers of ice.
  4. Falling to the ground: When the hailstones become too heavy for the updrafts to support, they fall to the ground as hail.

Factors Influencing Hail Size

Factors such as the strength of updrafts, length of time in the air, and size of hailstone can all impact the size of hail. The size of hailstones can vary greatly, from small pea-sized stones to large grapefruit-sized. On April 28, 2012 in St. Louis Missouri, there was record-breaking softball size hail. Several factors influence the size of hail:

  1. Updraft strength: Stronger updrafts can keep hailstones suspended in the thunderstorm cloud for longer periods, allowing them to grow larger.
  2. Duration in the cloud: The more time hailstones spend cycling through the updrafts and accumulating ice layers, the larger they can become.
  3. Available moisture: An abundance of supercooled water droplets within the thunderstorm cloud provides more opportunities for hailstones to grow.

Weather Patterns That Contribute to Hail Formation

Certain weather patterns are more likely to create the ideal conditions for hail formation:

  1. Supercell thunderstorms: These powerful, rotating thunderstorms are characterized by strong updrafts and can produce large hail.
  2. Frontal systems: The collision of warm and cold air masses along a front can trigger severe thunderstorms and hail.
  3. Orographic lifting: When moist air is forced upward by mountains or other elevated terrain, it can create instability and lead to hail-producing thunderstorms.


1. What is hail and how does it form?

Hail is a type of solid precipitation that forms during stormy weather when updrafts in thunderstorms carry raindrops upward into extremely cold areas of the atmosphere, turning them into ice balls.

2. Why does hail happen mostly in some places?

Hail happens more often in places where conditions are right for strong storms to form. This includes having lots of moisture, large temperature differences, and powerful updrafts which are common in certain regions known for severe meteorology events.

3. Can hail happen at any time of the year?

While hail can technically occur during any season, it’s most likely to happen during spring and summer months when storm formation is at its peak due to warmer temperatures generating stronger atmospheric instability.

Similar Posts