What causes hail, those frozen ice balls that fall during severe weather?
Hail is a form of precipitation, typically seen in the spring and summertime, that forms inside thunderstorms.
Thunderstorms are comprised of very large, towering, cumulus clouds, many of which can reach more than 50,000 feet up into the atmosphere. Within these clouds exist strong updrafts of air. These updrafts drag water droplets high up into the cloud where air temperatures are below freezing. This causes the water to freeze, creating small balls of ice.
These newly created hailstones grow larger and larger by colliding and coalescing with other frozen or nearly frozen water droplets within the cloud. Once the hailstones grow big enough and the updrafts within the cloud can no longer support them, they fall through the cloud and to the ground.
Measuring hail
Hail size is estimated and reported by comparing it with known objects.
These are the official size designations created by the National Weather Service.
- Pea = 1/4-inch diameter
- Mothball = 1/2-inch
- Penny = 3/4-inch
- Nickel = 7/8-inch
- Quarter = 1 inch — hail quarter size or larger is considered severe
- Ping-Pong Ball = 1 1/2 inches
- Golf Ball = 1 3/4 inches
- Tennis Ball = 2 1/2 inches
- Baseball = 2 3/4 inches
- Teacup = 3 inches
- Softball = 4 inches
- Grapefruit = 4 1/2 inches
What is the largest hailstone?
The largest recorded hailstone on record fell in Vivian, South Dakota on June 23, 2010.
Its diameter was 8 inches, circumference was greater than 18 inches and it weighed 1 pound, 15oz.
Related: What causes wind?
Hail can be incredibly damaging, especially as it grows in size. Hail has been known to cause extensive damage to automobiles, planes and homes. It can break windshields and leave cars with dozens of small dents.
Hail can also be extremely hazardous to livestock and people who may be caught in a storm without shelter.