If you’ve ever been caught somewhere during a spell of bad weather, you might have noticed tiny white balls, maybe smaller than beach pebbles, that fall from the sky. Eventually, these tiny balls accumulate in crunchy layers on the ground. On the other hand, you might have had to run for shelter to avoid being pelted by much larger balls of ice. Indeed, you might have been warned by your emergency broadcast system to find shelter for yourself, your car, or other equipment to avoid damage. One of these phenomena is called graupel, while the other is called hail. What’s the difference between them?
Differences Between Graupel and Hail
Here are some differences between these two phenomena.
|Small, 0.08 to 0.30 inches
|Can be much larger
|During winter storms
|Danger to people
|Can cause avalanches
|Large stones quite dangerous
More About Graupel
Graupel also goes by such sweet names as snow hail, snow pellets, or hominy snow. It happens when water droplets are cooled to below the point where they should turn to ice. These temperatures can be as low as – 40 degrees Fahrenheit. It is only when they fall on snowflakes that the water droplets freeze solid. This results in tiny balls that are between 0.08 and 0.30 inches around. When drops of water freeze on the snow crystals, they are called rime. As more rime accumulates on the snow crystal, it can lose its original snowflake shape and turn into a ball. This is graupel.
Besides being smaller and softer than hail, graupel can occur in different types of weather. It’s most often seen during snow storms, where it falls with ice pellets, or sleet. Ice pellets are slushier than graupel, and you may see them bouncing around on the ground after they hit. They also make tapping sounds when they strike an object where graupel is quieter. Though graupel usually appears in winter storms, it can also show up during warm-weather thunderstorms. It can even be seen falling with hail.
Graupel often forms above the mountains and can contribute to slab avalanches. This is when a weaker layer of snow lies beneath other layers. When it starts to go, it pulls the top layers down with it in a huge slab. The rime that forms on graupel gives it a low viscosity and a higher density than snow, which makes snow that’s already on a mountain slope slippery.
More About Hail
Hail is harder than graupel and can grow into very large balls, or stones. The largest hailstone, so far, was bigger than a softball and weighed nearly 2 pounds. This is more than enough to crack a car’s windshield or cause serious physical damage if it hits a living being. When it landed, this hailstone formed a 10 inch wide crater. Any ice crystal that falls from the sky and is 0.20 inches or larger is a hailstone.
These ice stones almost always form in powerful thunderstorms whose clouds are full of water droplets, have strong updrafts, and are at least partially below 32 degrees Fahrenheit, the freezing point of water. How big the hailstone gets depends on how the wind blows, how high up the cloud is, whether the hailstone impacts with rain or other hailstones, air friction, and how much it melts as it drops through the atmosphere.
Hail usually occurs in Earth’s temperate zones and is rare in climates that stay warm all year. This is true even though tropical climates have a fair share of powerful thunderstorms.
How it Forms
The updraft found in a storm cloud greatly impacts how a hailstone is formed. Updrafts lift the large water droplets into the cloud, where they can encounter temperatures below the freezing point but still stay as a liquid. If the droplet contacts something like a dust particle, it freezes instantly. As this newly formed bit of hail is bounced up into the cloud it puts on more layers of ice. Some of those layers are transparent and some are opaque. Sometimes, if you slice a hailstone in two, you can see concentric rings of clear and opaque ice, almost like the rings in a tree.
When the hailstone grows so large and heavy that the updraft can no longer support it, it falls. It can still grow as it drops through the cloud, though when it reaches warmer than freezing temperatures in the air it melts a bit. The larger the hailstone is, the faster it falls. A really large hailstone can fall as fast as 110 miles per hour.
Protection From Hail and Graupel
Because graupel is soft and cracks apart under pressure, it is not nearly as dangerous as large hailstones in ordinary life. However, because it’s been known to help trigger avalanches, you need to check the weather in advance if you’re going to go skiing or engage in any recreational activity on a snowy slope.
The way to protect yourself and loved ones from a hail storm is simple: find shelter beneath a strong roof. What’s problematic is protecting objects that can’t be brought into your house or other shelter. Here are some suggestions about what to do if a damaging hail storm is coming.
Protect Your Car
If you have neither a carport nor a garage for your car, don’t hesitate to take it to a place with a roof, such as a public parking garage. If even that’s not an option, cover your car with a blanket or a heavy, weatherproof cover. These covers not only protect the car from hail but from scratches and damage from water and ultraviolet light. If neither blankets nor weatherproof covers are available, try flattened cardboard boxes.
If you’re caught out in a hail storm when you’re on the road — and they can pop up quite suddenly — slow down, find cover, and pull over. Don’t park under trees whose heavy limbs can fall on your car, and don’t try and shelter beneath an overpass. Other drivers may have the same idea, and this can lead to accidents. Remember, visibility in a violent hailstorm is bad. You should also avoid low-lying areas that could be flooded.
If you can’t find proper shelter, angle your car in a way so that the windshield gets the brunt of the hailstones. Windshields are meant to be tough, but the other windows in your car are more fragile. While the storm lasts, lie down and protect your face from any glass that might break and fall in on you.
Protect Your Garden and Patio Furniture
If you have a garage or some kind of storage shed, put your garden and patio furniture, including pots and curios, inside. If you lack such storage, try and bring the items into your home for a while.
Cover Your Windows
If you’re at home, close the dressings over your windows. In case a hailstone breaks a window, it’ll keep the shards from being blown into the house.
Prune Your Trees
It’s always a good idea to remove dead or diseased branches from trees, but it’s especially important if there’s a hailstorm on the way. Hail can snap off even heavy branches that can cause damage to your home, your neighbor’s home, or power lines.
Before the Storm, Check the Weather
It’s always a good idea to check your local weather, even if you’re not planning on driving. If you are, checking the weather is a must.
After the Storm, Check Your House
When the storm is past, check your house, especially your roof, for dings, dents, cracks, missing shingles, or tiles. Fix small problems yourself if you can.
The photo featured at the top of this post is © Ben Romalis/Shutterstock.com
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