How dangerous is golf-ball-size hail?

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Dec. 12 2009 6:44 AM

How Dangerous Is Hail?

Can a grapefruit-size ice ball kill you?

Hail. Click image to expand.
How dangerous is golf-ball-size hail?

A nasty storm with 60 mph winds ravaged northern Pennsylvania on Wednesday. In Venango County, * there were reports of "golf-ball sized hail." In an "Explainer" column first published in 2006 and reprinted below, Daniel Engber wondered whether these falling chunks of ice were a major health risk.

Daniel Engber Daniel Engber

Daniel Engber is a columnist for Slate

At least 27 people died as tornadoes and hailstorms struck the Midwest and the South on Sunday. So far it seems like the strong winds—and not the "softball-sized" balls of falling ice—have done most of the damage. A tree fell on one person, another died when his mobile home rolled over, and a baby was blown down the street. Do giant hailstones ever kill anyone?

Yes, but it's very rare. Hailstorms have caused only a handful of deaths in the United States over the last 100 years or so; most of those killed were children. We have reports of one child dying from a hailstone strike in 1893 and another in 1928. A Texas farmer perished on account of hail in 1930, and babies had their skulls broken by balls of ice in 1979 and 1981.

Adults do get hit, but they're less likely to perish from their injuries. "I got hit so hard I thought I was going to pass out," one Fort Worth, Texas, victim of "softball-sized" hail told the Associated Press in 1995. "I started running and got hit in the head. Blood was everywhere," said another.

Hailstone deaths in other countries are somewhat more common. A few years ago, the Chinese government reported that at least seven people in Zhengzhou died in a storm of "egg-sized" hail. Dozens more ended up in the hospital. In Bangladesh, a giant storm of "grapefruit-sized" hail killed almost a hundred people in 1986. Some of the stones weighed more than 2 pounds.

Americans may be less likely to get killed by hail because we spend so much time indoors. (Weather patterns in North America may also make hailstorms less severe.) Animals that don't have this luxury tend to die in greater numbers. Individual hailstorms have killed dozens of horses and hundreds of chickens at a time in the United States. An 1888 storm in India is said to have wiped out more than 1,600 animals.

Three factors contribute to making a hailstorm especially dangerous: the size of the stones, the frequency with which they fall, and the wind speed. The killer hailstorm in Zhengzhou didn't have very big stones, but fierce winds pushed them earthward at very high speeds. More frequent hail increases your likelihood of getting hit in the head or another vulnerable spot. (Size and frequency trade off as a general rule: The bigger the hailstones, the fewer of them there are.)

Hailstones do come in different shapes, but there's little evidence that a spiky ball of ice does any more damage than a round sphere. Stones can also come in elongated forms, in cross-shapes, or with rings around the middle.

Bonus Explainer: How big is a softball-sized hailstone? About 4.5 inches in diameter. Climatologists don't like using balls and fruits to describe hailstones, since not everyone knows exactly how big a softball or grapefruit is supposed to be. (They prefer to use coins—dime-sized, nickel-sized, quarter-sized, and half-dollar-sized—as a point of reference.) Government weather services do have some guidelines: Grapefruit-sized hail is 4 inches in diameter, baseball-sized hail is 2.75 inches, golf-ball-sized hail is 1.75 inches, ping-pong-ball-sized hail is 1.5 inches, and pea-sized hail is less than half an inch in diameter.

Got a question about today's news? Ask the Explainer.

Explainer thanks Randy Cerveny of Arizona State University and Charles Knight of the University Corporation for Atmospheric Research. Thanks also to reader John Lilly for asking the question.

Correction, Dec. 13, 2009: This article originally misspelled the name Venango County, Penn. (Return to the corrected sentence.)

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