Extreme hailstone with an approximate 6-inch diameter, collected at 5:11 PM on Wednesday July 31, 2024, 4 miles northwest of Chokio, in Stevens County. Photo used with permission, courtesy of M. Benson.
Was it a record?
It's hard to say! The extreme hail reported near Chokio on July 31 is among the largest for which we have official records in Minnesota. After looking through the primary database for archiving hail and other weather hazards (here), and cross-referencing the largest reported hailstones with supplementary data, photographs, and historical documents, the stone that was approximately six inches across may be the largest hailstone on record for the state, though it has reasonable competition from at least four historical events. Confirming the record-holder is difficult because of the following considerations:- Many hail reports are "eyeballed," with the size compared to those of various coins, balls, or other spherical or rounded objects. Most hail reports are not based on measurements, but on these sorts of reference comparisons. "Softball-sized hail," therefore, certainly implies someone observed massive hailstones, but rarely means that hail was exactly the size of a softball. (Moreover, slow-pitch softballs are about 9% wider than those used for fast-pitch!)
- When hail is actually measured, it is (understandably) done with whatever is available, leading to different methods and different results. Some historical accounts report only the weight of the hail, which does not translate readily to other size measurements. An observer who has a stiff tape measure or ruler is likely to measure diameter (or longest distance across) only. An observer with a flexible tailor's tape may be able to measure the circumference. Many historical accounts include only one type of measurement, and we cannot make inferences about what the other measurement would be because hail is rarely a true sphere (see next).
- Although many hailstones are roughly ball-shaped, they rarely if ever are true spheres, which means we cannot assume a measurement of diameter corresponds to a certain circumference, or vice versa. This issue gets even more complicated by "aggregate" hail, which is the type of giant hail documented on July 31, 2024 (see picture above). Aggregate hail is often bumpy or "spiky," and even oblong, because it is made from the collision of multiple fast-moving hailstones that get glazed together as they travel through the storm cloud.
Very large hail statistics
Map of all reports of hail 4 inches in diameter or greater in Minnesota, from 1955 through July 31, 2024. Compliled from archived reports maintained by NOAA's Storm Prediction Center. Map produced by Sienna Ecker for the State Climatology Office.
- Two-inch diameter or greater: reported somewhere within the state 7-8 days per year, on average
- Three-inch diameter or greater: reported somewhere within the state 2-3 days per year, on average
- Four-inch diameter or greater: reported somewhere within the state about 5-6 days per decade, on average (39 days out of 70 years). This type of hail is quite extreme, and thankfully, somewhat rare (see image).
Historical "contenders" for the record hail size in Minnesota
The Storm Events Database and other official resources contain four previous hail events that could vie for largest on record in Minnesota.- June 13, 1956, 5" diameter hail in Pine County. A form submitted by the former State Climatologist and member of the US Weather Bureau at the time indicated that the hail destroyed "vehicle windshields and roofs." No measurements were indicated.
- October 14, 1966, Dodge County. This is unusually late for hail in Minnesota, let alone very large hail, but this day did feature an outbreak of tornadoes in Minnesota and Iowa (along with a snowstorm in northern Minnesota). A hailstone that crashed through a truck window in Dodge County was reported to have had a circumference of 16 inches and was called out in an official US Weather Bureau report to be an "all-time Minnesota hail size record." For a sphere, this would translate to a diameter of over five inches, but this may also have been aggregate hailstone, which would have made it highly non-spherical and potentially well over five inches across.
- July 4, 1968, 6" diameter hail in Murray County. The official report from that day indicates that hail was generally 1.25 inches in diameter but "some 6-inch hail reported with fields white with hail 4 inches deep." No further documentation found (yet).
- July 28, 1986, 6" diameter hail in Nobles County. The official report includes reference to hail the size of grapefruits and a circumference measurement of 13 inches. For a sphere that would translate to a diameter of just over four inches, but this may also have been aggregate hail, which would have made it highly non-spherical and potentially well over four inches across.