SIOUX FALLS, S.D. (KELO) — Almost everyone dreads hail. If you’re a homeowner, you worry about your windows, roof and siding. If you’re a renter, especially one without a garage, you worry about your car, sitting exposed in the parking lot or driveway. During the work day, most people’s cars are equally exposed throughout the day.

Hail is a common occurrence in South Dakota. In fact, the largest recovered hail stone in the U.S. fell in Vivian, S.D. in 2010. At the time, homeowner Les Scott, who recovered the stone, told KELOLAND meteorologist Jay Trobec over the phone that he intended to use it to make a daiquiri, but was dissuaded by the Aberdeen National Weather Service.

The hailstone was measured, and found to be the size of a melon, at 19-inches in diameter, and weighing in at about 2lbs.


Falling hailstones can pack a punch as anyone who has had to repair dents or a broken windshield can attest, but how hard and how fast do these stones actually fall?

According to the U.S. National Severe Storms Laboratory, the answer depends primarily on the size of the hailstone. For small stones under 1-inch in diameter, the NSSL says the expected fall speed in between 9 and 25 miles per hour.

For stones of 1-1.75-inches in diameter, such as what would be seen in a severe thunderstorm, the expected fall speed is between 25-40 mph.

In the strongest supercells, one might expect to see hail 2-4-inches in diameter, which the NSSL says can fall at speeds between 44 and 72 mph. It should be noted that variables such as hailstone shape, consistency, orientation and other environmental factors can change these speeds. However, the NSSL notes that it is possible for stones larger than 4-inches in diameter to fall at speeds of more than 100mph.

But what about the force these hailstones can hit with?

According to the International Association of Certified Home Inspectors (IACHI), the impact measured in joules, a unit of energy. IACHI says for instance, that 2-inch hailstone, falling at 72 mph, will carry 29.8 joules of impact energy.

To put that into perspective, the fastest MLB pitch ever reported clocked in at 105.1 mph, equating to 160.34 joules. A baseball measures in at just under 3-inches in diameter. The IACHI says a similar sized hailstone would clock in at 162.7 joules, meaning a baseball sized hailstone impacting an object would do so with roughly the same amount of energy as the MLB’s fastest ever pitch.

But what about that 19-inch hailstone in Vivian?

According to a website set up by a student researcher at the University of Vienna, the fall speed of a 48cm (19-inch), 46,325 gram (2lb) hailstone would be a staggering 239 km/h; or approximately 204.4 mph, about the top speed of the average NASCAR car.

In terms of energy, the Vivan hailstone would carry around 193,897 joules of impact energy.


In 2010, Scott reported extensive damage from the hail that hit his property, which left holes in his roof, and left holes as big as coffee cans in the ground.