Huge Hailstone Falls in South Dakota, Sets New Record

A massive hail stone nearly the size of a volleyball fell in a small South Dakota town this summer, setting the new record for the largest hailstone ever recorded.

The record setting hailstone was discovered in Vivian, measuring 8.0 inches in diameter, 18.625 inches in circumference, and weighing in at an amazing 1.9375 pounds.

This massive hail fell in the town of Vivian, South Daktoa on July 23, 2010.  The hail measured over 8 inches in diameter and weighed nearly 2 pounds.  Image Source:  National Weather Service.

This massive hail fell in the town of Vivian, South Daktoa on July 23, 2010. The hail measured over 8 inches in diameter and weighed nearly 2 pounds. Image Source: National Weather Service.

During a particularly violent thunderstorm on July 23, 2010, all of the town’s 55 homes were damaged, and one mobile home received 25 holes in its roof. Vivian, a town of about 110 people, is located 50 miles west of Chamberlain along Interstate 90 in central South Dakota.

The resident who located this stone in his yard quickly placed the hail in his freezer.  However, due to the severity of the storm, the electricity service was lost and the freezer was not powered for over 5 hours following the storm.  The resident who preserved the stone stated he felt it was closer to 10 to 11″ in diameter (rather than the later-measured 8 inches) at the time if fell.

    This massive hail fell in the town of Vivian, South Daktoa on July 23, 2010. The hail measured over 8 inches in diameter and weighed nearly 2 pounds. Image Source: National Weather Service.

This massive hail fell in the town of Vivian, South Daktoa on July 23, 2010. The hail measured over 8 inches in diameter and weighed nearly 2 pounds. Image Source: National Weather Service.

This hail stone shattered the previous record for size.  The former record was a hail stone that measured 7? in diameter and weighed closer to 1.6 pounds.  That stone fell in Aurora, Nebraska on June 22, 2003.  Prior to the Aurora, NE hailstone, the world record hailstone was from Coffeyville, Kansas.

The dynamics of a thunderstorm that is capable of producing such massive hail cannot be understated.  Hail forms as the updraft of a thunderstorm carries water droplets and ice crystals high in the sky.  The moisture is carried so high in the atmosphere that it freezes at high altitudes.  It eventually begins to fall and as it does so, it collects more moisture as it falls through the cloud.  This increases its size by giving it a coating of water.  If the hail stone gets caught up in the uprdraft again, it can make another trip up in the cloud, adding another layer of moisture which again freezes at high altitudes.  As this pattern continues, the hail stone becomes heavier, increasing the liklihood that the stone will fall from the cloud.  But if the updraft is strong enough, the stone may remain in the cloud for many, many cycles.  Initial estimates, based on the size of the stone, indicate that the updraft strength in the Vivian hail storm likely ranged from 160 to 180 miles per hour.

In the days following the storm, the hail stone was sent to the National Center for Atmospheric Research lab in Colorado for full documentation.  They certified the stone as the largest fully-documented hail stone in terms of weight (1.94 pounds) and diameter (8.0 inches).  Plans were made to construct a casting (mold) of the hail stone so that replicas could be displayed at the Historical Museum in Lyman County, South Dakota and at the Aberdeen, South Dakota National Weather Service Office.

Whether or not this is truly the largest hail stone to ever drop in the United States is a question that will remain unanswered.  What we do know is that it is at least the largest documented stone. Chances are a larger stone likely fell sometime in some location in the US but went undetected.

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