Understanding Hail: How Ice Balls Form in Thunderstorms

What is Hail?

Hail is a form of precipitation consisting of solid ice balls or lumps called hailstones. Unlike snow, which forms from water vapor freezing directly, hail requires powerful updrafts within thunderstorms to form. Hail can range from pea-sized (about 1/4 inch) to grapefruit-sized (4+ inches) in diameter.

How Does Hail Form?

Hail formation is a fascinating process:

1. Updraft Carries Water Upward: Strong updrafts in thunderstorms carry raindrops high into the atmosphere where temperatures are below freezing
2. Freezing Begins: Raindrops freeze on contact with particles like dust, forming the hailstone's center
3. Cyclone Development: Powerful updrafts keep hailstones suspended, where they collect more supercooled water droplets
4. Layering: Each trip through the freezing level adds another layer of ice, similar to tree rings
5. Gravity Wins: When hailstones become too heavy for the updraft to support, they fall to the ground

What Makes Some Storms Produce More Hail?

Not all thunderstorms produce hail. Conditions favoring large hail include:

• Strong updrafts: The faster the updraft, the longer hailstones stay aloft and grow
• High moisture content: More water available to form larger hailstones
• Deep freezing levels: Atmosphere must be cold enough at high altitudes
• Instability: Large temperature difference between surface and upper atmosphere

Hail Sizes and Damage Potential

Hail Safety Tips

• Seek shelter immediately when hail is reported or appears imminent
• Stay away from windows during severe hail
• Cover exposed body parts if caught outdoors with no shelter
• Protect vehicles by parking in garages when possible
• Wait 30 minutes after the last thunder before going outside

Source: National Weather Service, NOAA