What do you get when you mix moisture in the air with thunderclouds and strong winds? Many times the answer is hail.

Have you ever seen hailstones — sometimes tiny, sometimes large pellets of ice — fall from the sky? If you have, you know it can be quite a sight… and sometimes dangerous.

Hailstorms are most common in the warm spring and summer months. When thunderstorms and tornadoes increase, hailstorms usually follow close behind.

Cumulonimbus clouds — those tall, threatening clouds often called “thunderclouds” — are where hailstones begin to form. The temperatures high up in these clouds can be quite cold, causing moisture in the air to change into ice crystals. These ice crystals — sometimes called “soft hail” or “snow pellets” — are called “graupel” by meteorologists.

As graupel forms, the ice crystals become heavier and begin to fall downward. When weather conditions are right for hail, very strong winds — called “updrafts” — will push the graupel back up into the upper parts of the thunderclouds.

As the graupel ascends back into the upper parts of the thunderclouds, it accumulates more moisture and gets bigger. This process is called “accretion.”

As layers of ice are added, the graupel turns into hailstones that get bigger and again begin to fall toward the Earth.

When the hailstones grow big enough to overcome the power of the updrafts, they will fall to Earth as hail. How big hailstones get depends largely on how strong the winds are.

Updrafts of 20 miles per hour usually result in pea-sized hail (up to 0.5 inches in diameter), while updrafts of 40 miles per hour can make hailstones the size of quarters (up to 0.75 inches in diameter).

Very large hailstones require incredibly strong updrafts. Hail the size of a golf ball (up to 1.75 inches in diameter) needs updrafts of about 55 miles per hour. Softball-sized hail (4 or more inches in diameter) only forms when updrafts exceed 100 miles per hour.

The largest hailstone ever recorded in the United States fell in South Dakota on July 23, 2010. It weighed 1.93 pounds and measured 8 inches in diameter and 18.62 inches in circumference! Can you imagine the damage that hailstone could have caused?

Hailstorms usually don’t last long — only about 5 to 10 minutes — but they can cause a lot of damage in that time. In addition to damage caused to automobiles, airplanes, skylights and roofs, hail also regularly destroys farmers’ crops.

Far less common — but still possible — are serious injuries. Hail can cause concussions or fatal head trauma to people and animals if the hailstones are large enough.

Hailstorms are most common in the Great Plains states, especially northern Colorado and southern Wyoming. If a hailstorm breaks out where you live, get inside as quickly as possible and stay away from windows.

 

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  1. Hi Wonderopolis! Today’s wonder is very “heavy” with information about hail. It really doesn’t hail very often where I live, but if it does, we are usually inside.

    I think that tomorrow’s wonder is going to be about apples because they are sweet and they could be red or green.

    • Hi, Meredith! Hail storms can be exciting and a little scary sometimes! We think it’s best to stay indoors, too, and watch the WONDER of it all while still being safe! :-)

    • Welcome to Wonderopolis, Carlene! Thanks so much for commenting today and for letting us know that you learned something new from visiting today’s Wonder of the Day! :-)

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Have you ever wondered…

  • Why does it hail?
  • How big can hail get?
  • What is graupel?

Wonder Gallery

hail storm_shutterstock_259901Vimeo Video

Try It Out

Ready to get a hands-on, up-close idea of the different sizes hailstones can be? Search around the house and try to find as many of the objects on the list below as possible:

  • BB
  • pea
  • small marble
  • penny
  • nickel
  • dime
  • quarter
  • ping pong ball
  • golf ball
  • egg
  • tennis ball
  • baseball
  • orange
  • grapefruit
  • softball

Once you have as many of these items as you can find, line them up in order from smallest to largest. Finally, compare them to the most common sizes of hail listed in this estimating hail-size chart.

Think about what it would be like to be caught outside in a hailstorm. What size hailstones would do what kind of damage?

What would you do if you were caught in a hailstorm? Where might you seek shelter? Discuss storm safety with your friends and family.

 

Still Wondering

Check out Science NetLinks’ Hurricanes 1: The Science of Hurricanes lesson to learn more about the science of hurricanes and how forces change the speed and direction of motion.

 

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