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Good Question: Why Are Hailstones Different Sizes?

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(credit: CBS) Heather Brown
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MINNEAPOLIS (WCCO) – Many of you ended up with dents in your cars and roofs from all of the hail that came down last night. Reports ranged from hail the size of a pea to the size of a tennis ball.

“The last time I got hail like this was when I moved in 15 years ago,” said Ben Nicholls from Burnsville. The hailstones that fell in his yard were golf-ball sized.

So why are hailstones different sizes? Good Question.

According to WCCO Chief Meteorologist Chris Shaffer, it depends on the strength of the storm.

“You get these tremendous updrafts, so it can take water, kick it higher up in the atmosphere where the temperatures are far below freezing,” he said. “If those updrafts are strong enough, they’ll keep kicking around that particles.”

He said one of two things happen. First, if ice continues to accumulate on the super-cooled raindrops, you end up with smooth hailstones. Or, second, the hailstones in a very strong storm will collide into each other and pack together to create a jagged hailstone.

What gets a stone from pea-sized to grapefruit-sized is how long it’s in the air.

“If the updrafts are strong enough, they’ll keep them higher in the air longer and that will allow them to continue to grow,” Shaffer said. “Eventually gravity takes over and they fall back to Earth.”

The National Weather Service almost always reports hail in inches, but does offer a list of objects to which people can relate.

Penny, nickel, quarter, walnut, hen-egg, tennis ball, baseball, grapefruit.

“I think money comes in a lot because people have spare change in their pocket,” Shaffer said.

Once hail reports hit one inch in diameter, the National Weather Service considers that thunderstorm to go from normal to severe.

Shaffer said the biggest reported hailstone was right around 8 inches, the size of a small soccer ball on a farm in Vivian, South Dakota.

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