This afternoon and early evening I saw one of the larger outbreaks of hail I have seen in southern New England. The reports just kept coming in with more and more pictures of people holding hail. Some of the hail was quite large.
We don’t see much hail here in southern New England because our thunderstorms don’t often have the proper structure for the hail to form. This afternoon’s storms were strong enough to allow the hail to be created inside the core of the storms.
How Hail Forms
The basic idea of hail formation is the winds inside the storm, called updrafts, are so strong they carry a raindrop above the freezing line inside the storm. It is there that the rain freezes into ice. This process is completely different than sleet, a wintertime type of precipitation. Some people call sleet hail, but it’s not the same thing at all.
The image below shows how hail forms. Notice the rain getting carried high into atmosphere and freezing. There are different types of hail which depend on how much supercooled water, snow and ice are present in the cloud, but basically this is how hail forms.
Severe Weather Criteria
Hail one inch or greater in size is one of several criteria for severe thunderstorms. Strong winds are also another component of severe weather as are tornadoes. Torrential rain, which can cause problems, isn’t a criteria for severe weather.
On July 23, 2010, a severe thunderstorm struck Vivian, South Dakota. Large hail fell from the storm. The largest hail stone on record, even after some melting still measured 8 inches in diameter and weighed nearly 2 pounds (1 pound, 15 ounces) with a circumference of 18.62 inches.
According the National Weather Service, “small hail, up to about the size of a pea, can wipe out a field of ripening grain or tear a vegetable garden to shreds. Large hail, the size of a tennis ball or larger, can fall at speeds faster than 100 miles per hour and can batter rooftops”