This past week, Arkansas experienced a very destructive hail storm that likely caused millions of dollars in damages. Portions of west central, and central, Arkansas were the most effected. Some areas saw hail sizes larger than baseball size! This is not common, in fact most hail stones remain at pea or marble size. We received several messages regarding the hail storm after the fact, with many questions as to "why it occurred, where hail even comes from, and how did it get this big?".
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| Extremely large hail stones that fell in White Hall on March 10th, 2018. |
Hail is defined as pellets of frozen rain that fall in showers from cumulonimbus clouds. This may sound like a rather boring, or bleak phenomenon, but we assure it is not! Hail is precipitation that is formed when updrafts in thunderstorms carry raindrops vertically into very cold portions of the atmosphere. Hail can damage aircraft, homes, cars, and can be deadly to livestock and people. Hailstones grow by collision with super-cooled water droplets. Super-cooled droplets are liquid drops surrounded by air that is below freezing, this is a common occurrence in thunderstorms.
Strong updrafts create a rain-free base in super cellular thunderstorms. This rain free base is referred as a WER, which stands for "weak echo region". The term (WER) stems due to the presence of a rain free region of a thunderstorm which is bounded on one side, and above by very intense precipitation indicted by a strong echo on radar.
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| The idealized path of hail within cloud. |
This rain-free region is produced by the updraft and is what suspends rain and hail aloft producing the strong radar echo. The hailstone is carried aloft by the updraft and begins to grow in size as it collides with other super-cooled rain droplets and other small pieces of hail. During this process, some hail stones can actually be blown out of the updraft itself, thus falling to the earths surface.
If the updraft is stronger, it can actually move the hailstone back into the cloud where it once again collides with cooled droplets and other small hail stones. This process may be repeated several times, depending on the strength and longevity of a storm. However, hail stones will eventually no longer be supported by the updraft and fall to the earth. The LARGER the updraft, the larger sizes of hail can be expected.
Super cellular thunderstorms can grow to heights over 40,000 feet tall. As you climb in latitude, the atmospheres temperature will decrease. This is the reason for the strong and destructive hail as it reaches very high latitudes, and then falls to the earth.
Believe it or not, there is a proper way to size and measure hail stones. As we stated earlier, we experienced hail stones larger than baseball size over the last week! We've included a graphic (posted above) to help relate this measurement theory. Although softball size hail is very rare, it has occurred before, even in Arkansas. The largest hailstone ever recorded fell during a severe thunderstorm that struck Vivian, South Dakota on July 23, 2010. The hailstone measured 8.0” in diameter, 18 ½” in circumference, and weighed in at 1.9375 pounds.
We hope you enjoyed this edition of "Spring Severe Season 101", this is our second entry and only the beginning! Share this with your friends, and let's spread the awareness regarding the weather we experience!
References: https://www.weather.gov/ - https://www.wunderground.com/blog/weatherhistorian/worlds-largest-hailstones.html
