Steve Horstmeyer's Severe Weather Primer Part 11 - Hail

Steve Horstmeyer's Severe Weather Primer Part 11 - Hail

. - Steve Horstmeyer's Severe Weather Primer Part 11- Hail
This is the final post of my 11 part series on severe weather.

***** This is a re-posting of Part 11 of my Severe Weather Primer. At the beginning I have added photos from the large hail that fell in the FOX19 NOW viewing area the evening of October 19, 2016.  *****

Hail: Southeast Indiana October 19, 2016

Thunderstorms and Hail
Hail is a good indicator of thunderstorm strength and the larger the hail the stronger the thunderstorm. Without a doubt the thunderstorms that produced the giants below were at the top end of cumulonimbus development.

From July 6, 1928 until September 1970 Potter, Nebraska was famous around the world for being the location that the largest measured hailstone fell.  It measured around 7 inches (17.8 centimeters) in diameter and weighed about 1.5 pounds (680 grams). Some of the big hailstones that fell that day were photographed by J.J. Norcross owner of the Potter Drug Company. He placed them on 10-ounce soda fountain glass tumblers. His image shown below is from Monthly Weather Review, August, 1928. The stone on the far right is the record setter with a circumference of 17", weighing in at 1.5 pounds. On the far left is an even larger stone that Mr. Norcross described as two stones frozen together. Which for reasons not mentioned did not count as the largest stone.

Early on the evening of September 3, 1970, Potter Nebraska was erased from the record books when the heaviest and largest hailstone on record fell in Coffeyville, Kansas. The new record setting hailstone measured 17.5 inches in circumference, weighed 1.67 pounds and scientists estimated that it struck the ground at the speed of 105 MPH leaving a divot 9 inches wide and one to two inches deep (image below).

Fast forward 33-years and on June 22, 2003 a behemoth hailstone plunged from a thunderstorm faster than a major league fastball in Aurora, Nebraska. The largest-hailstone-in-the-world record returned to the Cornhusker State. The National Climate Extremes Committee validated the stone's measurements taken by the National Weather Service forecast office in Hastings, Nebraska and new record-holder was certified. With a diameter of 7 inches and a circumference of 18.75 inches, the Aurora, Nebraska stone surpassed the Coffeyville, Kansas stone that fell  on September 3, 1970 (images below)

No record lasts forever and on July 23, 2010 the record for largest hailstone moved to Vivian, South Dakota. Les Scott saw it fall and observed what he called "fingers" sticking out of the stone. He ventured out, retrieved the stone and had visions of making making daiquiris from the ice. After thinking about it he called the National Weather Service and  the NWS team from Aberdeen, South Dakota  came up with a weight of 1.9 pounds, a circumference of 18.622 inches and a diameter of 7.9 inches.

So here is how the biggest hailstone record book stands at of this writing, April 8, 2016:

Heaviest Hailstone: 2.25 pounds, Gopalganj District, Bangladesh, 14 April 1986.

Largest Diameter: 7.9 inches, Vivian, South Dakota, 23 July, 2010.

Largest Circumference: 18.74", Aurora, Nebraska, 22 June 2002.

UA WHATU  or HUKA-A-WHATU - A Bit of Hail Science History
The Maori of New Zealand called hail rain stones (ua whatu) or stones like snow (huka-a-whatu). How ice could fall from the sky on a hot summer day mystified many ancient cultures who often defaulted to a god's wrath to explain a damaging hailstorm.

Anaxagoras (499-427 BC), the Greek philosopher, was getting close to being a scientist and being right too, when he used observations to explain hail.

First he observed air, smoke, ash and debris shoot upward above fires. He also observed that mountain tops are colder than lower elevations. Anaxagoras put the two together to reason that air lifted when the sun the heated Earth's surface rose to great heights where it was colder than freezing allowing water to freeze and hail to form. 

It would be another 2200 years before the next big step in explaining how growing clouds worked when James Pollard Espy wrote about temperature decrease of rising air in the 1840s.

Aristotle rejected the ideas of Anaxagoras because, he reasoned, that if hail formed high in the cloud it would be found on mountain tops and hail was not found there. Aristotle considered heat and cold to be opposites and in conflict. In warm months because there was so much heat cold air was "squeezed" into small intense concentrations that would freeze the hail. Like most other phenomena in the atmosphere Aristotle was wrong about hail too.


Today we know how hail forms and clues to the process are visible in the image below.

First observe that the hailstone above formed in  nearly concentric layers. Also observe some layers are made of clear ice and and others are milky white ice. A closer look would reveal a distinct center to the stone and finally there are some spikes or fingers that look like icicles, 

  • 1. The layers tell us this hailstone grew by a process where water (frozen and solid) was added incrementally.
  • 2. The clear vs. milky ice tell us there are two ways ice is added. Milky white ice, called rime ice, is added through direct deposition from vapor in air colder than freezing. The clear ice is added as a layer of liquid water in warmer  regions of the cloud then freezes in colder air.
  • 3. The distinct center tells us there was an original object new ice was added to. This is called the hail embryo and can be a small hailstone, an insect, graupel or other object.
  • 4. The spikes were probably made of water flowing across the surface of the stone following air flow around the stone as it fell. It seems likely the spikes formed in the up direction as the water was pushed around the falling stone.