A Brief History
On April 14, 1986, the Gopalganj district of Bangladesh experienced the largest hailstones ever recorded, with an incredible weight of 1 kilogram for a single hailstone! As you can imagine, the damage caused was extensive, but even worse, 92 people were killed by the giant ice balls from above. Today we take a look at this particular weather phenomenon.
Hail is basically frozen rain. Little balls of ice, or irregular shaped lumps, hail differs from ice pellets in that ice pellets usually fall in the winter or cold weather and are smaller. Hail varies in size from little BB sized balls to lumps big enough to kill people and livestock, and cause serious damage to buildings and property, or even crops. Ice falling from the sky is usually classified as hail when it is at least 5mm in diameter (about a fifth of an inch). Hail forms in the coldest portions of the clouds, falls to lower portions, picks up more moisture and rotates back up, often in a series of multiple trips gaining a new layer each time it performs the trip up and down in the cloud. The more trips, the bigger the hail. (Of course, other factors also affect the size of the hail, such as the humidity of the cloud, the temperature of the upper and lower portions of the cloud, etc.) The position of the hail in the cloud also has an effect on how the hail is formed, as well as the speed by which the growing hailstone rises and falls, which can be well over 100 mph! Eventually the hail is too heavy to continue its upward journey and it falls from the cloud as a form of frozen precipitation.
At least this above explanation was the theory, while more recent research indicates other factors might be at work in the formation of hail. Normally hailstones partially melt when in the lower reaches of the cloud, and refreeze when in the upper, colder portions. At times, the partial melting does not take place and the hailstones develop a white, opaque color instead of a more transparent/translucent tone.
In any case, when the hailstone reaches a size that can no longer be carried upward by the updraft, it falls, usually picking up some more mass on the way down through the cloud. This falling usually starts at a fairly high altitude, about 10,000 meters (33,000 feet). Many technical weather details such as air temperature, humidity, and other factors such as proximity to a coast all affect whether or not hail is formed. (We will leave the technical stuff here, as it is more complicated than we care to get into.) The Great Plains of North America is the region most prone to receiving hail, especially large, damaging hail.
What our readers want to know, is how fast is this hail when it is hitting us on the noggin? The velocity that hail falls is largely a function of its size. Bigger hail falls faster, which is bad news if big hail is falling. Small hailstones might reach only 20 mph of velocity, while larger ones (3 inch diameter) can fall at well over 100 mph. Imagine a baseball sized hailstone hitting your head (or roof or top of your car) as fast as the fastest major league pitcher can throw a baseball. Wow! It is easy to see how serious the damage can get.
Aside from the aforementioned record heavyweight hailstones that fell on Bangladesh in 1986 (1 kilo), other hail records include the largest diameter of 7.9 inches (South Dakota, 2010) and the largest circumference of 18.74 inches (Nebraska, 2003). Continental interior areas away from the coast and at moderately high altitudes are most prone to receiving hail storms, with the most hail prone location on Earth being found in Kericho, Kenya, in the Westernmost (most inland) part of the country at about 7200 feet altitude that gets about 50 days of hail each year. The record number of days of hail in one year for a single location is also Kericho, 132 days of hail in a single year!
Sometimes so much hail falls that the ground is covered, kind of like snow in the summer. The stuff can take some weird shapes, too. The largest hail this author ever saw in Ohio was distinctly football shaped, a little over an inch long and around a half inch in diameter. Notable hail storms included one that left hail 18 inches deep, though an accumulation of 2 inches or more is considered a lot. In 2010, Colorado experienced a hailstorm that left hail a foot deep on the ground. In 2015, a single city block of Denver, Colorado found itself under 4 feet of ice balls! (The worst hail this author ever experienced was in the mountains of Colorado in 1976, with ping pong ball sized stones that hurt so bad we sought cover under a rock ledge, fearing serious injury.) In the 9th Century in India, a hailstorm dropping hailstones “the size of cricket balls” (similar in size to a baseball) killed as many as 600 people.
Like many natural phenomena, hail is a complex and interesting process, though having to replace a car or roof on your house might not be so “interesting.” If you have any interesting tales of hail, please share them with us in the comments section.
Question for students (and subscribers): What is the largest sized hailstone you have ever seen? Please let us know in the comments section below this article.
Your readership is much appreciated!
For more information, please see…
Blum, Andrew. The Weather Machine: A Journey Inside the Forecast. HarperCollins Publishers, 2019.
Henning, Ryan. Field Guide to the Weather: Learn to Identify Clouds and Storms, Forecast the Weather, and Stay Safe. Adventure Publications, 2019.
The featured image in this article, a photograph by the National Severe Storms Laboratory (NSSL) Collection of an aggregate hailstone, is in the public domain because it contains materials that originally came from the U.S. National Oceanic and Atmospheric Administration, taken or made as part of an employee’s official duties.