From The Weather Channel (Simone M. Scully):
It’s important to know about hailstorms so you can avoid injury and stay safe during one:
1. Hail is a form of precipitation — like rain or snow — that is made up of solid ice.
2. It is not the same thing as frozen rain.
Frozen rain falls as water but freezes as it gets near the ground.
Hail falls as a solid, known as hailstone.
3. Hailstones are formed when rain droplets are carried upwards by a current of air, called an updraft, during thunderstorms.
“Hail forms as robust thunderstorms grow taller and taller, lofting moisture up into the atmosphere where it freezes,” explains Jonathan Belles, digital meteorologist at Weather.com.
4. “The stronger the thunderstorm, the larger the hail can get,” says Belles.
That’s because hailstones grow in size as the frozen moisture droplets collide with surrounding water vapor, causing that water to freeze on the hailstone’s surface in layers.
A frozen droplet will start to fall back towards earth from a storm cloud, then be pushed back up into the cloud by an updraft, hitting rain droplets — which freeze on its surface — as it moves.
Winds inside a thunderstorm aren’t just up and down, though, especially in severe storms. There are horizontal winds, such as rotating updrafts in supercell thunderstorms, which can move the hailstone too and affect how it grows.
Eventually, the hail does fall to the ground. This happens, Belles explains, “when updrafts can no longer support the weight of the hailstones.”
5. Hailstones can be clear or cloudy.
It all depends on how the hailstone forms: If the hailstone collides with water droplets and they freeze instantaneously, cloudy ice will form because air bubbles will be trapped inside it.
If the water freezes more slowly, air bubbles will be able to escape and the ice will be clearer.
They can also have layers of clear and cloudy ice as the hailstone experiences different conditions in the thunderstorm.
6. Hail size is often estimated by comparing it to a known object.
For example, hail that is ¼ inch in diameter is referred to as pea-size, hail that is 1-inch in diameter is called a quarter-size, and hail that is 4 inches in diameter is softball-size.
“Most hailstones are small, generally pea size,” says Belles. “The National Weather Service considers hail dangerous to life and property when the stones reach about the size of quarters. We typically see hail up to softball size several times a year.”
It’s worth noting, however, that most hailstorms are made up of a mix of different sizes.
7. The largest hailstone ever recovered in the United States was 8 inches in diameter and had a circumference of 18.62 inches.
According to the National Severe Storms Laboratory (NSSL), it weighed 1lb. 15 oz. and it fell in Vivian, South Dakota [do you have a date for when this happened? Might be good for reference].
8. The speed that hail falls depends on a lot of things.
The speed depends on the size of the hailstone, the friction between the hailstone and surrounding air, the local wind conditions and whether or not the hailstone starts to melt.
According to NSSL, small hailstones under an inch usually fall at speeds between 9 and 25mph, whereas hailstones of an inch to 1.75-inches in diameter typically fall faster — between 25-40mph. The strongest supercells, which can produce hail between 2 and 4 inches in diameter, can cause hail to fall at speeds of 44-72mph.
9. Hail storms can happen all year long.
“Hail can form at any time of the year as long as the thunderstorms are strong enough,” explains Belles. “While the biggest hail is often associated with severe thunderstorms in the Plains and Southeast from February to June or July, hail is also common in the cooler season along the West Coast as storm systems take advantage of the winter cold air.”
From 2009-2018, May and June averaged nearly 3000 reports of severe hail, which the National Weather Service classifies as being one inch or larger in diameter.
10. Some regions do get more hailstorms than others — and it’s not necessarily the regions that get the most thunderstorms.
Florida is a very thunderstorm-prone state, but it’s not actually the place where hail storms are most common.
“Hail is most likely from the Dakotas to Texas during the course of the year,” explains Belles. “This is the location where the strongest thunderstorms overlap with cold air aloft and fast winds in the jet stream.”
The area where Nebraska, Colorado and Wyoming meet is known as “hail alley” and it averages seven to nine hail days per year, according to NSSL. Colorado experiences the greatest damage from hail storms, followed by Texas, Illinois, Minnesota and Missouri, according to the Insurance Information Institute.
Abroad, China, Russia, India and northern Italy get frequent hail storms too.
11. Hail falls in paths called “hail swaths.”
These can be seen from the airplanes and they occur as thunderstorms move while the hail falls.
According to NSSL, hail swaths can range in size from just a few acres to an area 10 miles wide and 100 miles long.
12. Hail storms can cause significant damage.
Hailstones can cause a lot of damage to buildings, vehicles, crops and livestock.
In fact, hail causes approximately $1 billion in property and crop damage every year in the United States. One of the costliest hail storms in the country hit Denver, Colorado in July 1990 and caused $625 million in damage. A 2016 study by the Highway Loss Data Institute found that insurance companies paid $5.37 billion in total hail claims to automotive policy holders.
While quarter-size hail will cause damage to shingles, golf ball-size hail can cause dents on cars and baseball-sized hail can smash windshields. Softball sized hail, meanwhile, can cause holes in roofs.
While reported human deaths from being struck by hail are somewhat rare in North America, they do happen. In 2000 a man in Fort Worth, Texas was killed when he was struck by softball-sized hailstone.
Hail storms can also cause severe injuries. On average, an estimated 24 people are injured by large hail each year, but sometimes, there can be a lot of injuries from one storm. For example, a May 1995 hailstorm in Texas injured 400 people when they were caught outside during Mayfest with very little shelter available; 60 of those injured required hospitalization.
Even hail storms that produce a lot of small hail can be dangerous because all those hailstones can completely cover roads. If these hail piles are deep enough, they can prevent car tires from touching the road at all. This makes driving conditions similar to icy winters.
13. It’s tough to forecast when a hailstorm might occur in advance.
“We usually have a few days heads up that conditions might be ripe for hail, but we don’t know that any community will have hail until an hour or so before it occurs,” says Belles.
14. The best way to protect yourself from a hailstorm is to be prepared, especially if you live in a hail-prone region.
“We all should have our storm kits well-stocked throughout the year,” says Belles, and those storm kits should include helmets. “[They] can help you save your head from both the hail itself and the debris that can also come with severe thunderstorms.”
It’s also a good idea to make a disaster preparedness plan for your family so that you all know where to go for safety and how to contact each other after an emergency.
If severe weather occurs, such as a bad thunderstorm, tune in to the radio or another news source to make sure you stay up to date of any immediate threats to your family or property.
15. If you get caught outside in a hail storm, seek shelter indoors.
Make sure you stay inside until the hail stops and stay away from skylights and windows. Close the drapes or curtains if you have them to keep broken glass and hailstones out of your home. It’s also best to seek shelter at least one level down from the roof.
If you’re driving, pull over as soon as possible, preferably by near a place with shelter, like a garage or under a gas station awning. Make sure you’re completely off of the highway.
“If you’re caught in a hail storm in your car with no sturdy structures nearby, please stay in your car and cover yourself if possible,” Belles says. “While windows may break, the car should keep your head safe.”
If you’re outside and you can’t find shelter, find something to at least protect your head and stay out of ditches or lowland areas because they could fill with water. Avoid trees because they can lose branches during thunderstorms and isolated trees can also attract lightning.