8 Inch Hail Falling From the Sky? How Large Hail is Formed (Credit: NWS Aberdeen and NSSL)

On July 23, 2010, a hailstone that shattered records fell in Vivian, South Dakota. This hailstone weighed roughly 1.9375 lbs and was 8 inches in diameter. A typical hailstone is nowhere near this large, so how did a phenomena like this occur?

Hail is formed as water droplets are lifted higher into the thunderstorm into very cold air, allowing these droplets to freeze. The frozen droplets collide and interact with supercooled water droplets that freeze on contact, allowing for the hailstone to grow. The hailstone continues to grow as it continues to collide with supercooled water droplets within the cloud until it becomes too large for the thunderstorm's updraft to support. At this point, the hail will fall through the cloud, often colliding with other hailstones on its way down, before falling to the ground. 

But what is an updraft, and how does it relate to larger hail? An updraft is upward moving air that helps with the formation and sustaining of thunderstorms. A thunderstorm’s updraft will lift warm, moist air into the storm to fuel and sustain the storm. It also carries water droplets higher into the storm. Stronger updrafts would be able to lift water droplets higher and into colder parts of the storm than weaker updrafts. Stronger updrafts would also be able to keep larger hailstones aloft for longer. Because of these factors, stronger updrafts would lead to larger hailstones. And if you have a strong enough updraft, hailstones such as the record breaking one in Vivian, SD can form. 

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©2019 Meteorologist Stephanie Edwards