Sunday, February 8, 2015


Hail falls from large cumulonimbus clouds made of water drops and ice particles.

"A hailstone starts out as an ice particle. Ice particles build up into ice crystals by condensation. The ice crystals are blown up and down inside the cloud by very strong air currents, and as they are thrown around, they absorb more and more cloud drops. The cloud drops freeze onto the ice crystals in layers, like the skins of an onion. When they freeze near the warmer, lower part of the cloud, they freeze fairly slowly, and spread out as a layer of clear ice. When they freeze near the higher, colder part of the cloud, they freeze instantly, making a layer of frosty ice. By counting the layers of ice in a hailstone, we can tell how many times it was blown up and down inside the cloud, just as we can tell how old a tree is by counting the rings in its trunk. The more violent the air currents are, the taller the cloud will grow, and the bigger the hailstones are likely to be. Most hailstones are less than two inches in diameter, but they grow much larger on occasions." (Francis Wilson and Harold Gibson, Spotters Guide to the Weather, Usborne Publishing Company, 1979.)
Hailstorms occasionally happen in Utah, but most events cover only a relatively small area of the state. The largest and most damaging hailstorms usually occur during the warmer months of May through September when towering thunderstorms pass over the state.
Three of the most severe hailstorms ever recorded in Utah occurred along the Wasatch Front:
On August 19, 1945, thunderstorms associated with the remnants of a Pacific hurricane produced hailstones up to two inches in diameter which bombarded the Salt Lake Valley, killing birds, damaging trees, homes and stores, and causing extensive damage to nearly 50 airplanes at the Salt Lake City Airport.
On July 21, 1987, one to two inch diameter hailstones injured a dozen people and damaged numerous cars in Utah County. Baseball size hail fell in Coalville. Wind and hail severely damaged or destroyed much of the fruit crop in Utah County. Damage estimated totaled about $9,000,000.
On August 4, 1991, one-half inch diameter hail fell for about 15 minutes to a depth of three inches at Snowbird. Forty-three people were injured when the hail and rain cause a large canvas canopy to collapse on 1,400 people watching a performance of the Utah Symphony.
Much of the information for this section originally appeared in the copyrighted book Utah's Weather and Climate, edited by Dan Pope and Clayton Brough, in 1996. UCCW Directors have received permission from the copyright owners of this book to reproduce such information on its website and to revise and updated it where appropriate.

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