Snow

Let It Snow!

The coolest form of precipitation is snow. Snow falls when water in the atmosphere freezes and forms crystals that fall to the ground. Snow accumulation varies from a light dusting to a dumping of a meter or more. Pretty, flaky, and fun, snow is important to climate. Many animals and people depend on it to live. But snow has a dark side. Slippery, snowy roads make driving dangerous. People die in avalanches and from cold exposure. Just shoveling heavy snow off a sidewalk can be dangerous for someone with health problems.

Mountains accumulate a lot of snow.

Mountains accumulate a lot of snow. An area of naturally-formed, packed snow and ice that hasn’t melted yet is called snowpack, and mountains get the deepest snowpacks.

©G.Ellis/GLOBIO.org

Forming a Flake

The lacy arms of this complex snowflake are called dendrites

The lacy arms of this complex snowflake are called dendrites. The snowflake is almost the same on all sides. It is called a symmetrical flake. Different environmental conditions such as temperature help form symmetrical or uneven snowflakes.

©Jasper Nance

Water in the atmosphere is in the form of a gas called water vapor. When water vapor is cooled high in the sky, it condenses around tiny particles of dust into water droplets. These droplets clump together into a cloud. If it’s cold enough, some of the droplets freeze into ice crystals. More molecules of water vapor condense and freeze on the surface of the crystal. Eventually the crystals grow into snowflakes heavy enough to fall from the cloud.

Different Shapes from Different Conditions

Temperature and the amount of water vapor in the air affect snow crystal formation. The colder and drier it is, the simpler the shape. With more water vapor and warmer temperatures, crystals can grow into lacy, frilly flakes. Wind affects the shape of snowflakes too. If winds are light, the flakes can grow larger than when they are knocked around by high winds.

Simple to Complex

The snowflake on the right is a simple star crystal.

The snowflake on the right is a simple star crystal. The one on the left is more complex. Which snowflake do you think formed in warmer temperatures?

©Jasper Nance

The simplest crystal shape is a hexagon. The crystals may be flat like plates or shaped like columns with six surfaces, like a pencil. From this shape, additional water molecules can grab on and freeze, branching out to form lacy arms. These crystals are called dendrites. Dendrites may be shaped like stars or have branches that resemble ferns. Other crystal shapes include needles, triangles, and bullets. Scientists can grow snow crystals in a lab. These “designer” snowflakes help scientists better understand how crystals form in nature.

Made by Machine

If you’ve ever been skiing or snowboarding, you know that snow can also be made by machines. Snow makers turn air and water into snow so that people can ski even when the weather doesn’t cooperate. Snow from a snow maker is not made of crystals at all, but tiny frozen ice pellets. The machine breaks up a stream of water into droplets and cools them off as it blows them out onto the slope. Tractors then move and shape the snow to cover the slopes.

Ski and snowboarding resorts around the world have machines that make snow so people can enjoy playing in the snow whenever they want.

Ski and snowboarding resorts around the world have machines that make snow so people can enjoy playing in the snow whenever they want. Another machine that makes “snow” is a snow cone or shave ice maker.

©Anders Ljungberg

Where on Earth Does It Snow?

Look at a map of the earth and imagine a belt circling the equator. In this area, at sea level, snow doesn’t usually fall. However, even here snow can fall at high elevations where cold temperatures keep it from melting before reaching the ground.

The water and land at Earth’s North and South Poles are always covered in snow and ice, but the air is so dry that the snowfall is really quite low. High winds blow the existing snow around, making it seem like it’s snowing when it isn’t. The Arctic Circle (North Pole) is mostly ice-covered ocean but also includes parts of Canada, Iceland, Russia, Alaska, and all of Greenland. Ice covers land on the continent of Antarctica (South Pole).

Where Snow Never Melts

Glaciers are made of ice and snow and store the largest amount of fresh water on Earth.

Glaciers are made of ice and snow and store the largest amount of fresh water on Earth. The largest glaciers are continental ice sheets and Antarctica is one of the only places where they exist.

©G.Ellis/GLOBIO.org

In spring and summer, snow melts at lower elevations and outside the polar regions. But snow never melts in some places. It gets packed into thick layers of ice called glaciers. You can think of a glacier as a very slow-moving river of ice. Antarctica has the most glaciers, but they are also found in the Arctic Circle, and at high elevations such as the South American Andes, the European Alps, and Tanzania’s Mt. Kilimanjaro.

A Flurry of Snow Terms

Small hail collecting on the ground can sometimes be confused with snow

Small hail collecting on the ground can sometimes be confused with snow. Hail can be much larger and cause damage to property. When it’s large, it’s best to run for cover!

©Michael Henderson

Some types of precipitation seem like snow, but really aren’t. Sleet is the term for raindrops that freeze before they hit the ground. So what’s freezing rain? That’s rain that reaches the ground in drops, THEN freezes on contact. Some scientists also define sleet as snow crystals that have melted and refrozen on their way to the ground. In either case, sleet is made of ice pellets, not crystals, and is not a form of snow. Hail is also not a form of snow. Hail is made up of balls of ice that have several layers. A frozen raindrop can swirl around in a storm cloud and gather more water that clings to it and freezes. When the raindrop or hail hits the ground, it can be as small as a pea or as large as a plum. Hail falls during severe thunderstorms.

Blizzards and Avalanches

You’ve probably heard of a blizzard—a windy snow storm that lasts a long time and dumps a lot of snow. But have you heard of a ground blizzard? That’s when high winds lift already fallen snow from the ground and swirl it around. Both types of blizzards can create dangerous whiteout conditions, where the snow is so heavy you can’t see very far.

There are several kinds of snow avalanche and different things can trigger the slide

There are several kinds of snow avalanche and different things can trigger the slide. The photo above shows the largest kind, a powder avalanche. A falling piece of rock or ice may have begun the loose snow’s destructive release.

©C.Monteath/Hedgehog House/Minden Pictures

When huge amounts of snow slide off the slope of a mountain, it’s called an avalanche. Avalanches occur when the top layer of snow gets too heavy for the snow at the bottom to “hang on” any longer. The snow breaks free and falls, covering anything in its path. Vibrations from earthquakes or weapons fire can also trigger an avalanche. A huge avalanche caused by an earthquake in China destroyed a whole town in 1970, killing 18,000 people. Avalanches kill 150 people every year, and injure many more.

Snow Birds

Many animals are well adapted to live in snow. One adaptation is that they change color to better blend in to their snowy surroundings. Foxes, hares, and birds such as grouse and ptarmigans all grow white fur or feathers for winter—even on their feet. The wider furry or feathery feet act like snowshoes, keeping animals on top of the snow instead of sinking.

In the winter, the Arctic fox’s fur changes from gray to white. The coat’s color change helps the fox stay hidden when hunting. The prey won’t see the fox until it’s too late.

In the winter, the Arctic fox’s fur changes from gray to white. The coat’s color change helps the fox stay hidden when hunting. The prey won’t see the fox until it’s too late.

©K.Campbell/GLOBIO.org

Snug in the Snow

Many animals rely on snow as shelter. Mice, hares, grouse, and ptarmigans make snow burrows in which they can rest and be protected from wind. Snow is a good insulator. It traps warmth from the ground which keeps it and anything else under the snow blanket several degrees warmer than it is on top of the snow. The layer of air and snow pack just above the ground in which animals tunnel and burrow is called pukak.

Plants benefit from the insulating ability of snow too. During winter plants go dormant. But even if a plant looks dead above the ground, its roots are protected under the soil and snow. When the snow melts and the plants can get enough sunshine, they “wake up” and begin growing. Farmers may use manmade snow to protect crops from freezing.

Winter Fun and Water Source

Despite snow’s dangers, it has many benefits. For one thing, snow can be a lot of fun. You know this if you’ve ever thrown a snowball, built a snowman or snow fort, or made snow angels. Sports such as skiing, snowboarding, sledding, and snowmobiling wouldn’t exist without snow, and resorts with snowy slopes and trails are big business.

In some parts of the world, kids like to play in the snow when the temperature isn’t too cold

In some parts of the world, kids like to play in the snow when the temperature isn’t too cold. Some animals enjoy playing in the snow too.

©Bruce Dennis

Snow is also very important as a source of water for many people. When snow melts each spring, the water that runs off fills streams and rivers that provide drinking water. In some places, snowmelt accounts for three-quarters of the water in streams. This is also why shrinking glaciers are a concern. Glaciers store most of the world’s fresh water in the form of ice. Global warming is causing many glaciers to melt, which may lead to rises in sea level worldwide. At the same time, rivers the glaciers feed may recede or dry up.

They Know Their Snow

Scientists study how seasonal snowpack affects plants and animals

Scientists study how seasonal snowpack affects plants and animals. Getting samples during this time of year can be a lot of cold work!

©Courtney Meier

We already mentioned scientists who study snowflakes and their delicate structure. Weather scientists or meteorologists study snow and weather patterns to try to predict snowfalls. Other scientists study snow to learn about climate, especially climate change. Because snow and ice are very sensitive to temperature, they are indicators of change. Scientists measure snow depth and use images from satellites to track the size of glaciers. Aside from the water snow provides, it is also important in keeping the earth cool. It does this by reflecting sunlight. Snow and ice reflect up to 90 percent of the Sun’s energy. Without that reflection, the energy would get absorbed by the ground, making it even warmer. Studying snow is serious business, but snow scientists probably still like a good snowball fight!