What you need to know

Hailstones can grow from pea-sized pellets to softball-sized projectiles capable of punching through car windshields and roofs. The size a hailstone reaches depends almost entirely on one factor: the strength of the thunderstorm's updraft. Stronger updrafts keep hail aloft longer, allowing it to cycle through layers of supercooled water and build mass with each pass.

Hail forms inside severe thunderstorms when updrafts—columns of rising air—carry raindrops into subfreezing layers of the atmosphere. As the droplet freezes and falls, the updraft can loft it back up, coating it with another layer of ice. This cycle repeats until the hailstone becomes too heavy for the updraft to support, at which point it falls to the ground.

Understanding how hail grows helps explain why some storms produce golf balls while others drop baseballs—and why the largest hailstones on record have all come from supercell thunderstorms with exceptionally strong updrafts.

How does hail form inside a thunderstorm?

Hail begins as a frozen raindrop or ice pellet, called an embryo, in the upper reaches of a thunderstorm where temperatures drop below freezing. For hail to grow beyond a few millimeters, the storm needs three ingredients:

  • A strong updraft (typically 40+ mph, but the largest hail requires updrafts exceeding 100 mph)
  • Abundant supercooled water—liquid droplets that remain unfrozen despite being colder than 32°F
  • Sufficient storm depth, usually at least 30,000 feet from base to top

As the embryo is suspended or lofted by the updraft, it collides with supercooled water droplets. These droplets freeze on contact, adding a thin layer of ice. The hailstone may fall slightly, then get caught in the updraft again and carried back into the supercooled zone, repeating the process.

Each trip through the storm adds another layer. If you slice a large hailstone in half, you'll often see concentric rings of clear and opaque ice, much like the rings of a tree. Clear layers form when water freezes slowly, allowing air bubbles to escape. Opaque (milky) layers form when water freezes rapidly, trapping air.

What determines how large hail can grow?

The maximum size of a hailstone is governed by updraft strength. A hailstone will keep growing as long as the updraft can support its weight. Once the stone becomes too heavy, gravity wins and it falls out of the storm.

The relationship is straightforward: stronger updrafts can suspend heavier hailstones for longer periods, giving them more time to accumulate ice. According to the National Severe Storms Laboratory (NSSL), updrafts of around 50 mph can support golf ball–sized hail. Baseball-sized hail (2.75 inches) requires updrafts near 80 mph. Softball-sized hail (4+ inches) demands updrafts exceeding 100 mph—velocities found only in the most intense supercell thunderstorms.

Supercells are rotating thunderstorms with a persistent, organized updraft. They're responsible for nearly all hail larger than two inches in diameter. The rotation helps organize the updraft and can create a tilted structure that allows hailstones to cycle through the storm multiple times without immediately falling out.

How many times does a hailstone cycle through the updraft?

The number of cycles varies. Small hail may make only one or two passes. Large hail—especially stones approaching softball size—may cycle five, ten, or even more times through the storm's core.

Each cycle doesn't necessarily add the same amount of mass. Early in the hailstone's life, when it's small and light, the updraft can carry it high into regions with less supercooled water, resulting in thinner layers. As the stone grows heavier, it may spend more time in the "sweet spot" of the storm—a zone rich in supercooled water where accretion is most efficient.

Researchers have used dual-polarization radar to track the trajectories of large hailstones inside supercells. These studies, including work published by NSSL, show that the largest hail often originates in a region called the "hail growth zone," located on the forward flank of the supercell where updraft and supercooled water content are both maximized.

What are the largest hailstones ever recorded?

The United States holds multiple records for giant hail. The current record for the largest hailstone by diameter fell in Vivian, South Dakota, on July 23, 2010. It was roughly the size of a volleyball and weighed just under two pounds. The stone was slightly flattened on impact, and scientists believe it may have been even larger before hitting the ground.

Other record-holders include:

  • Coffeyville, Kansas (September 3, 1970): The previous record before Vivian
  • Aurora, Nebraska (June 22, 2003): 7.0 inches in circumference, weighing 1.33 pounds
  • Bethune, Colorado (August 13, 2019): The largest hailstone recorded in Colorado

All of these stones fell from supercell thunderstorms with radar-estimated updraft speeds well over 100 mph. The Vivian storm, for example, was a violent supercell that also produced tornadoes and wind gusts exceeding 80 mph.

How much damage does large hail cause each year?

Hail is one of the costliest severe weather hazards in the United States. According to NOAA's National Centers for Environmental Information (NCEI), hail causes an average of $1.6 billion in property and crop damage annually. That figure has been rising in recent decades, driven by increased property values, urban sprawl into hail-prone regions, and improved reporting.

Hail larger than one inch in diameter is considered severe by the National Weather Service (NWS). Stones this size can dent vehicles, damage roofs, and shatter windows. Hail two inches or larger—roughly the size of a hen's egg or tennis ball—can cause catastrophic damage to structures, puncture metal roofs, and injure or kill livestock and people caught outdoors.

The most damaging hailstorms in U.S. history include:

  • April 10, 2001 — A supercell produced baseball-sized hail across the Kansas City metro, causing over $2 billion in insured losses (adjusted for inflation)
  • May 5, 2017 — Golf ball to tennis ball–sized hail fell across the Denver metro, resulting in $2.3 billion in damage, the costliest hailstorm in U.S. history

Hail also poses a significant threat to agriculture. A single hailstorm can destroy an entire season's crop in minutes. Wheat, corn, and cotton are especially vulnerable. The central Plains—including Kansas, Nebraska, and eastern Colorado—experience some of the highest hail frequencies in the world, a region sometimes called "Hail Alley."

Why don't all severe thunderstorms produce large hail?

Not every severe thunderstorm has the structure or dynamics to grow large hail. Storms with weak or disorganized updrafts may produce small hail or none at all. Storms that form in environments with high cloud bases—common in the desert Southwest—often allow hail to melt before reaching the ground, a phenomenon called sublimation.

Supercells are the most efficient hail producers because their rotating updrafts are both strong and persistent. Non-supercell storms, such as squall lines or pulse thunderstorms, can produce hail, but it's typically smaller and shorter-lived.

Temperature and moisture profiles also matter. Storms that form in environments with a deep layer of subfreezing air (a "cold cloud depth" of 20,000 feet or more) are more likely to produce hail. Conversely, storms that form in warm, tropical air masses—common along the Gulf Coast in summer—may produce heavy rain and tornadoes but little to no hail, because the freezing level is too high.

Can you predict where large hail will fall?

Forecasters can identify environments favorable for large hail hours or even days in advance, but pinpointing exactly where a hailstone will land remains difficult. The Storm Prediction Center (SPC) issues outlooks that include hail probabilities, and the NWS issues severe thunderstorm warnings when radar detects hail signatures.

Dual-polarization radar has improved hail detection significantly. By measuring the size and shape of precipitation particles, radar can estimate hail size with reasonable accuracy. When radar detects a "three-body scatter spike"—a signature indicating very large hail—the NWS may issue a warning specifically mentioning "destructive hail" or "baseball-sized hail."

Despite these advances, hail remains one of the hardest severe weather hazards to forecast with precision. A supercell may produce softball-sized hail in one location and pea-sized hail just a few miles away, depending on subtle variations in updraft strength and storm structure.

What should you do if large hail is approaching?

If a severe thunderstorm warning mentions large hail, take these steps immediately:

  • Get indoors and stay away from windows and skylights
  • Move vehicles into a garage if possible; hail larger than golf ball size can total a car
  • Avoid taking shelter under trees or carports, which offer little protection from large hail
  • If caught outside or driving, pull over and cover your head; do not attempt to outrun the storm

Large hail often falls in a narrow swath, sometimes only a few hundred yards wide. If you're on the edge of the warned area, the difference between no damage and catastrophic damage can be a matter of blocks.

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