If you’ve lived in Colorado for more than a season, there’s a good chance you’ve heard hail rattle your roof, crack your car windshield, or shred your garden. From the Eastern Plains to the Denver Metro and up into the foothills, hail is a common—and costly—part of life here. But how exactly does hail form, and why is Colorado such a hotspot for it? Let’s break down the science behind those icy missiles from the sky.
What Is Hail?
Hail is a form of solid ice precipitation that develops inside strong thunderstorm updrafts. Unlike sleet or freezing rain, hail forms during warm-season storms, not winter weather. Hailstones can damage homes, vehicles, aircraft, and crops, and pose serious threats to people and animals caught outdoors.
How Hail Forms Inside Storms
- The Updraft Effect
It all starts with a strong updraft—a column of rising air inside a thunderstorm. These updrafts can be powerful enough to lift raindrops high into the storm, well above the freezing level. - Supercooled Water & Ice Nuclei
At high altitudes (where temperatures are below freezing), the raindrops freeze into tiny ice pellets. These become the “seeds” of hailstones. - Layering and Growth
As these small hailstones are kept aloft, they collide with supercooled water droplets—liquid water that exists below freezing. When these droplets freeze on contact, they add layers to the hailstone.- If the water freezes instantly, it traps air bubbles, creating cloudy ice.
- If it freezes slowly, the air escapes, and the result is clear ice.
- The Fall
Eventually, the hail becomes too heavy for the updraft to support. When gravity wins, the hailstone falls toward Earth—sometimes straight down, but often at an angle or even sideways if surface winds are strong.
How Fast Does Hail Fall?
The speed depends on the size and shape of the hailstone, along with air resistance and melting:
- Pea-sized hail (¼ inch): ~9–25 mph
- Quarter to golf ball (1–1.75 inches): ~25–40 mph
- Baseball to softball (2–4 inches): ~44–72 mph
- Massive hail (>4 inches): Can exceed 100 mph
Larger hail tends to fall more vertically, close to the storm’s updraft, while smaller stones can be blown farther away.
Why Is Colorado a Hail Hotspot?
Colorado sits in the heart of “Hail Alley”, along with Nebraska and Wyoming. This region sees 7 to 9 hail days per year on average, the most in North America. Despite Florida having more thunderstorms overall, the combination of elevation, dry air aloft, and strong upslope winds gives Colorado prime conditions for hail-producing storms.
Hail Swaths and Hail Drifts
As storms move, they can leave long hail swaths—tracks of hail that cover large areas, sometimes over 100 miles long. Some storms produce such intense hail that it clogs drains and forms hail drifts, much like snowdrifts. These can become feet deep, completely covering roads and making travel treacherous.
How Big Can Hail Get?
The largest U.S. hailstone was recorded in Vivian, South Dakota in 2010:
- Diameter: 8 inches
- Circumference: 18.62 inches
- Weight: 1 lb 15 oz
In Colorado, hailstones over 2 inches (golf ball size and larger) are not uncommon in severe storms and often cause major damage.
Size Comparison Guide:
- Quarter = 1 inch (severe threshold)
- Ping-Pong Ball = 1.5 inches
- Golf Ball = 1.75 inches
- Baseball = 2.75 inches
- Softball = 4 inches
- Grapefruit = 4.5 inches
Staying Safe During a Hailstorm
- Seek shelter: Indoors or in a vehicle is safest.
- Protect animals: Livestock and pets are especially vulnerable.
- Report hail: Use known object comparisons or, better yet, measure with a ruler or tape measure.
Bottom Line for Coloradans
Hail is a part of life here, but understanding how it forms and falls can help you stay safe and prepare better. From the powerful updrafts to the icy layers forming high above, each hailstone tells the story of a storm—and now, you know how to read it.