BETHUNE — A state record was broken on August 13th, when a hailstone measuring 4.83" fell near Bethune, Colorado. As impressive as this is, what's even more shocking is the storm updraft speed needed to form a hailstone this large.
Hail is formed by a storm updraft, a vertically moving column of air that feeds a thunderstorm. Water moving through an updraft will turn into rain drops and freeze when it gets high enough into the storm.
Some of these ice pellets fall out of the storm and melt as rain, but some of them get stuck in the updraft and grow large enough that the updraft can no longer hold them in the air, falling out as hail.
Weak storms will have weak, slow moving updrafts ranging between 10 to 30 mph. Supercells and other very strong storms will have much faster updrafts, with speeds of 60, 70, 80, even over 100 mph!
Below is a chart from the National Weather Service that gives rough estimates of how strong storm updrafts need to be to create various sizes of hail.
As you can see, a softball sized hailstone, which is 4.5 inches, needs an approximate updraft speed of 103 mph to form.
With the new record hailstone being even larger than a softball at 4.83" in diameter, it's likely the storm updraft that produced this hail was moving around 110 mph, or 9,680 feet per minute!
To put that in perspective, the air is moving so fast vertically through the storm, it would be like climbing from the bottom of the Barr Trail to Barr Camp in one minute.
The picture above shows radar indications of 65dbz (hail stones ranging from a quarter in size to tennis balls) being shoved 30,000 feet in the air, or about 1,000 feet higher than the summit of Mount Everest.
