BUMPED WITH UPDATE 2:25pm Friday: Within the last hour, a three-automobile relay brought the giant hailstone (8″ in diameter, 1.94 pounds) to the lab of hail expert Dr. Charles Knight in Boulder, CO. They are going to make a plaster cast so replicas can be made for display at several museums.
Here is what the storm looked like on radar with the location of the town of Vivian marked by dot. (click to enlarge)
This is one of several giant hailstones that fell near Rapid City, SD. Hailstones of this size (based on calculations at StormTrack.org) fall through the air at about 200 mph!
One of many holes punched in roofs by the giant stones.
The updraft in the thunderstorm would have been around 150 mph. An airplane could be torn apart by flying into an updraft of that intensity which is why pilots need to give thunderstorms a wide berth.
is reporting that NOAA is going to certify this was the largest hailstone in U.S. history.