NOAA National Weather Service Weather Forecast Office

Hail Safety

Hail is made up of spherical balls of ice that fall from thunderstorms. Hail forms as the result of small frozen raindrops or graupel being continuously recycled through multiple up- and downdrafts. They continuously accumulate new layers of ice until they become so heavy that they can no longer be supported. Hail is not to be confused with sleet, which is frozen raindrops that fall during winter storms.  The map below shows the annual number of days with hail in Wyoming based on a national map by Changnon (1977). The southeastern

corner of Wyoming lies within the nations "Hail Alley". Together with adjacent portions of Colorado and Nebraska, this region of Wyoming is battered by more hailstorms than any other part of the United States. 

As far as the element of hail, The National Weather Service classifies a storm as severe if hail of 3/4 of an inch in diameter (approximately the size of a penny) or greater is imminent based on radar intensities or observed by a spotter or other people.  If hail begins to fall at your location it is important to move indoors immediately.  Stay away from windows which can be broken by the falling hail.  Hard topped vehicles offer good protection until the size of the hail reaches golf ball diameter.  Although hail rarely causes fatalities it is the most destructive element associated with thunderstorms.  Hail causes approximately $1 Billion in damage to property and crops annually.  Consult our handy reference chart to estimate the size of hailstones.

The hailstone shown here fell near Aurora, Nebraska on June 23, 2003.  Although its weight of 1.33 pounds did not set a world record, the stone did set other records.  The stone was 7.0 inches in diameter and measured 18.75 inches in circumference, both world records.  The storm that produced this stone was a supercell.  Click here for more information about this amazing event.