Definition of Hail storms, Hailstones, and Hail Alley

Hail

Hail is precipitation in the form of a chunk of ice that can fall from a cumulonimbus cloud. Usually associated with multicell, supercell and cold front induced squall line thunderstorms, most hail falls from the central region of a cloud in a severe storm.

Hail begins as tiny ice pellets that collide with water droplets. The optimum freezing level for the formation of hail is from 8,000 to 10,000 feet.

The water droplets attach themselves to the ice pellets and begin to freeze as strong updraft winds toss the pellets and droplets back up into the colder regions of the upper levels of the cloud. As the attached droplets freeze, the pellets become larger.

Both gravity and downdraft thunderstorm winds pull the pellets back down, where they encounter more droplets that attach and freeze as the pellets are thrown, once again, back up through the cloud.

Hailstones
The more times a hailstone is tossed up and down through the cloud, the larger the hailstone will be. Hailstones the size of softballs had many more trips up and down through the cloud than pea-sized hailstones.

Large hailstones are an indication of powerful updraft and downdraft winds within a thunderstorm. This is why large hail is associated with severe thunderstorms.

To create pea-size hail (about 1/2 inch in diameter) winds within the thunderstorm updraft will generally be around 20 miles per hour. Quarter size hail (3/4 of an inch in diameter) requires updrafts of about 40 miles per hour.

Golf ball size hail (1 3/4 inches in diameter) needs updrafts of around 55 miles per hour and softball size hail, approximately 100 miles per hour!

The largest hailstone ever measured in the United States fell at Coffeyville, Kansas, on September 3, 1970. It weighed 1.67 pounds and measured 17.5 inches in circumference. http://www.agiweb.org/geotimes/june00/hailstones.html

Hail Alley
The Great Plains states, especially northeastern Colorado and southeastern Wyoming, receive more hail yearly than any other part of the United States. Hail in this area of the country is most likely to fall late in the afternoon during the months of May and June and is often responsible for extensive crop loss, property damage and livestock deaths.

Hail storms are frequent occurrences across the U.S. Since 1988, there have been on average nearly 3,000 individual hail events reported each year. The majority of hail storms occur between March and June. The states experiencing the most frequent hail include: Colorado, Wyoming, Nebraska, Kansas, Texas, and Oklahoma.