On July 23, 2010, a severe thunderstorm struck Vivian, South Dakota, USA, a quiet rural community of less than 200. While there was nothing unusual about a violent summer storm, the softball (and larger)-sized hail that accompanied it was extraordinary. In fact, it led to the discovery of the largest hailstone ever recorded in the United States.

Once the thunderstorm passed, Vivian resident Les Scott ventured outside to see if there was any damage as a result of the storm. He was surprised to see a tremendous number of large hailstones on the ground, including one about the size of a volleyball. Scott gathered up that stone, along with a few smaller ones, and placed them in his freezer.

How does hail form?

• Inside of a thunderstorm are strong updrafts of warm air and downdrafts of cold air.
• If a water droplet is picked up by the updrafts…it can be carried well into colder zones and the water droplet freezes.
• As the frozen droplet begins to fall, carried by cold downdrafts, it may partially thaw as it moves into warmer air toward the bottom of the thunderstorm
• But, if the little half-frozen droplet get picked up again by another updraft and is carried back into very cold air it will re-freeze. With each trip above and below the freezing level our frozen droplet adds another layer of ice.
• Finally, the frozen hail, with many layers of ice, much like the rings in a tree falls to the ground.

According to NOAA, the Kansas City hail storm on April 10, 2001 was the costliest hail storm in the U.S. which caused damages of an estimated $2 billion.

Image from NOAA

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