From the National Weather Service
New Record Hail Event: NOAA’s National Climate Extremes Committee with support from WFO Aberdeen, WFO Cheyenne and Central Region SSD Climate Services, has declared a hailstone in Vivian, SD, to be the largest in diameter and heaviest ever recovered in the United States.
Found after a July 23, 2010, severe thunderstorm by Vivian resident Les Scott, the hailstone is 8.0 inches in diameter and weighs 1.9375 pounds (1 pound, 15 ounces) with a circumference of 18.62 inches.
These measurements displace the previous hailstone record for weight, previously 1.67 pounds for a stone in Coffeyville, KS, in 1970. They also surpass the record for diameter, which was 7 inches for a hailstone found in Aurora, NE, in 2003. The Aurora hailstone still holds the record for circumference of 18.75 inches.
The world record heaviest hailstone was in the Gopalganj District of Bangladesh on April 14, 1986. The stone weighed 2.25 lb. (http://wmo.asu.edu/).
A modern day “Pony Express” carried the hailstone from Vivian, SD to Valentine, NE and onto Cheyenne, WY. It was then handed off to the Colorado State Climatologist who transported the stone to the National Center for Atmospheric Research in Boulder, CO. They have created casts of the stone for future display. The original stone will likely be returned to Les Scott.