Blair from Oklahoma reminded me of a news report that I read a few days ago about a record breaking hail stone that fell in Vivian, South Dakota, during a 23-July severe thunderstorm. According to NOAA, the hailstone weighed in one ounce short of 2 pounds, had a diameter of 8 inches, and a circumference slightly greater than 18 inches, nearly the size of a soccer ball.
Leslie Scott found the giant hailstone while surveying the damage around his ranch. He said the stone was actually several inches bigger than the final measurement, since it had melted somewhat. Hailstones punched through the roofs of structures and sounded like bricks being smashed. Large impressions were left in the ground where they landed.
What makes a hailstone?
A hailstone forms from moisture that is drawn up from muggy warm air that is near the ground by way of updrafts which reach high up into a growing storm. The moisture freezes into ice crystals (it’s very cold up there, as cold as -50 degrees F). The ice pellets begin to fall, but instead of reaching the ground they get pulled back up into the cloud from updrafts. This process keeps repeating until the updraft simply cannot support the weight of the hailstone any longer, at which time they fall to the ground. For hailstones to form the size that was recorded in Vivian, South Dakota, the updrafts had to have been enormously powerful.
Average annual number of hail days in the U.S.
Hail the size of a penny requires updraft winds of about 40 mph for formation. Golf ball size hail requires about 65 mph, while softball size hail needs about 100 mph updrafts to form. So, we know that this storm had updrafts exceeding 100 mph.
The intensity of a hailstorm depends on the the size of the hailstones, the number of hailstones, and the speed of the wind when it hails. Hail falls from the sky at various speeds depending on it’s density, the friction imposed by it’s shape, collisions with other hailstones, and the updrafts that exist around it. Because of this, most hail never reaches terminal velocity, about 120 mph, but I have seen calculations in the range of 70 mph. The record breaking hailstone in Vivian likely achieved a very high speed during it’s fall, and this article from examiner.com claims it may have fallen at least 100 mph and possibly up to 175 mph.
U.S. hail pattern based on diameter of averaged sized hailstones in inches
Hail can cause major crop damage, property damage, and can even kill you. Reading the article about the recent severe hailstorm in South Dakota should remind those of you who are living in these risk areas to be wary of the skies. Do not be caught outside, away from protection of falling hailstones. Depending on the size, you may not even be safe in your vehicle or even in your home (stay away from the 2nd floor, and windows)!
To see some examples of the power from hailstorms, just do a search on youtube. Some of the video is amazing. Blair, a reader from Oklahoma had sent me this link awhile ago. Have a look – it’s crazy.
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