Published: 2010-08-02 07:55:37
Updated: 2010-08-02 07:55:37
Posted August 2, 2010
By Mike Moss
Back on July 23rd, a tremendously intense supercell thunderstorm blasted the town of Vivian, SD with what sounds like an amazing hailstorm, and in its aftermath, a resident named Les Scott found a hailstone that has since been confirmed, by NOAA's National Climate Extremes Committee, as the largest in diameter and heaviest on record for the United States. The stone was placed in a freezer shortly after it was found, but the severity of the storm meant there was no power and so it was probably a little larger even than the officially reported maximum diameter of 8 inches and weight of 1.94 pounds. It is worth noting that its maximum circumference was 18.62 inches, and this still trails the circumference of 18.75 inches for a hailstone found in Aurora, CO in 2003.
That distinction highlights the fact that very large hailstones are typically aggregates made up of many smaller stones that stuck together and were coated and cemented with layers of freezing supercooled water in a complex process that often results in a decidedly non-spherical final product, one that, as in the picture of the new record stone, is sometimes studded with lumps and protuberances as well. Another interesting note with regards to this stone is that NOAA estimates that the thunderstorm updraft required to suspend it long enough to reach this size had to be in the range of 160-180 mph. Apparently, there were many hailstones in this event that reached or exceeded 6 inches in diameter, resulting in a lot of serious damage to homes, businesses and vehicles, as well as a few injuries.
I've included links to a NWS storm summary about this event that includes some interesting radar imagery and a couple of other photos, to a story in the Rapid City Journal that expands a bit on the impacts around Vivian and the way it was experienced by some of the residents, and to the website of the National Climate Extremes Committee.
Around here, we almost had a new record to report as well. After notching the warmest June on record for the Raleigh-Durham airport, the month of July ended up close but but just shy of a new mark, with the average temperature for the month ending up at 82.3 degrees Fahrenheit. This left it tied with July of 2005, and two tenths of a degree cooler than July 1993, when the average temperature was 82.5.