How full of the creative genius is the air in which these are generated! I should hardly admire more if real stars fell and lodged on my coat

Henry David Thoreau

I love the snow. That means that I’m a chionophile.

I’m a Canadian, living in the north where snow falls and stays for close to six months of the year, from November to April. In the Kawartha region of Ontario, where I currently live, I daily walk the riparian forest along the river and marsh and in the deep of winter this is no different. What I’ve come to understand is that each winter day is different and each day is a gift. The gift could be a sudden shower of glittering snow dust in a cedar forest, releasing a cascade of jewels in the sunlight. Or the passion of a heavy first snowfall in early winter that covers everything, including me, in a blanket of soft beauty. Or the glittering sea of surface hoar covering a snowfield on a fresh sun-kissed morning.

When I was a child, I learned from my older sister how to stick out my tongue and taste the snow as it floated down in heaps or to catch a hexagonal snowflake on my coat sleeve to examine it. I learned about the different kinds of snow, the best kind for making snowballs or snowmen and snow forts. The kind best used for playing ‘kick the can’ (dry snow made on a very cold day that is packed but light as Styrofoam) and the kind best left alone (wet snow turned into a dense cake of ice through successive melting and refreezing).

Old snow is called firn, which is often dense with snow that has recrystallized through thaw and refreezing. Recently, I walked through firnspiegel. Firnspiegal means ‘glacier mirror’ in German, a term that my German mother used to describe a thin brittle plate of ice that forms when surface snow melts then freezes. In the morning, Firnspiegel forms a sheet that gleams like glass under a raking sun. On a recent morning, frost had formed over the firnspiegel, adding a sea of glitter. As I walked through it into powder below, the thin sheet broke into tiny shards that tinkled like glass.  If the layer thickens, it becomes solid enough to support your weight. Norwegians call it skare. But watch for the holes previously punched by someone. When I was a young girl, I broke my ankle tripping into one as I watched the birds and not where I was stepping.

Winter this year in the Kawarthas has been particularly cold and full of precipitation. A lot of that has fallen as snow. The snow stands in high piles by the roadside, reminding me of the deep snow winters of my youth in Granby and Montreal. To get my quintessential shot I must wade through high snowbanks, often plunging over my knees. From there, I carve fresh tracks through an open expanse of freshly fallen snow and drift, leaving a trail of deep prints. It’s hard work but invigorating.

I breathe hard with exertion and excitement by the time I reach my worthwhile prize: the sun-kissed glitter of deep blue water and ice pancakes loitering at the edge of the river; a hoarfrost-covered gnarly shrub that looks like a fairytale; or a barchan-shaped snow drift that releases snow glitter to a cold wind.  

What Is Snow & Frost?

Snow crystals and frost crystals are both ice crystals that grow from water vapour in the air. Snow crystals form from water vapor that sticks to suspended dust particles high in the clouds that fall to thee ground; frost crystals form from water vapour near the ground (often fog), that sticks to cold surfaces. Both snow and frost reflect the original six-sided symmetry typical of the water molecule.

Frost is a lot more common than most people realize. This is because we often mistake it for snow—partly because frost actually forms on snow in the form of surface hoar. This is hoar frost that develops as water vapor migrates up through the snow base on cold, clear nights. Surface hoar is responsible for the beautiful glitter we often see on snow on a cold morning. It also forms on the glassy surface of melted than refrozen snow, firnspiegel, both conspiring to create even more glitter.

On a calm clear and cold night, hoar frost will form. Hoar frost can resemble tiny frozen leaves or ferns, and typically forms on leaf edges, fence posts, and branches and buds of trees. It also forms on ice. Humid air will skip the droplet stage and go straight to crystallizing. When the sky is clear, the temperature can quickly drop since there are no clouds providing insulation. That’s when the magic of hoar frost happens and you wake up to the glitter of frost leaves. I recently found a bed of hoarfrost ‘flowers’ forming on the older ice of Thompson Creek marsh.  

Unlike hoar frost, rime frost forms during a freezing fog. Rime formations are also denser, longer versions of hoar frost. The dense super-cooling water vapor freezes on any surface it comes in contact with. Tiny ice crystals in the freezing fog may even form light snowflakes that fall to the ground and accumulate in a fine layer of fluffy ‘dust.’ Meteorologist Cory Reppenhagen calls these “fog flakes” or “stealth flakes.” Rime may look like hoar frost, with long spikes if there is no wind, or thick dense aggregations if there is wind. So, when you wake up on a cold winter morning and see all the trees covered in silvery frost, to differentiate, you’d have to know the conditions that formed them: they may be hoar frost (if it was a clear cold night) or rime frost (if there was a freezing fog).

Snow & What We Call it

Snow can fall as individual snowflakes or as larger clumps of flakes. Once on the ground, snow can take on different qualities depending on local temperature, wind and moisture, and how long the snow has been on the ground. Fresh snow is often powdery and loose while old snow may have crusty layers from melting and refreezing. We often characterize snow by the amount of water it contains. There is dry snow (0% water), moist snow (less than 3%), wet snow (between 3-8%), very wet snow (between 8-15%), and, finally, slush (15% water).

Skiers like my son characterize snow conditions for skiing, such as: fresh snow, powder (POW), packed snow, hard-packed or icy pistes, slush snow, crud and corn snow, choppy snow, and sticky snow. Skier/boarder vernacular has evolved some interesting terms such as: pow (great powder snow); face shot (when the pow is so deep it hits you in the face); gnarly or gnar (dangerous or challenging in a good way); shredding (carving through pow on a hill as in “shred the gnar”); mashed potatoes (mushy spring snow), and freshies (first tracks).

The table below describes different classes of snow and frost and how they form.

TYPE	DESCRIPTION
Snow crystals	Single ice crystals, often in six-fold symmetrical shapes, that if large enough can be considered a snowflake. These grow directly from condensing water vapor in the air (unlike sleet, which is frozen raindrops), usually around a nucleus of dust or some other foreign material. Typical sizes range from microscopic to a few millimeters in diameter.
Snowflakes	Single large snow crystal or collections of snow crystals, loosely bound together in a polycrystal. These can grow to a large size (up to 10 cm), especially when the snow is wet and sticky. A snowflake may consist of up to 100 snow crystals clumped together.
Snow Rime	Snow crystals accumulate rime when they collide with water droplets in the clouds.
Graupel	Loose collections of frozen water droplets, sometimes called ‘soft hail’ with the consistency of Styrofoam. Snowflakes that become rounded, opaque pellets (from 2-5 mm in diameter) that form as ice crystals fall through supercooled below freezing cloud droplets that remain a liquid. The cloud droplets freeze into crystals, forming a lumpy mass. Graupel looks like hail but is softer and more crumbly. Graupel forms in mild air temperature of 15 to 25F and reflects unstable, convective conditions similar to a thunderstorm.
Hail	Large, solid chunks of ice.
Window frost	Forms when a pane of glass is exposed to below-freezing temperatures outside and moist air on the inside. Water vapor in air condenses as frost on the inside surface of the window. Elaborate patterns can emerge based on the window surface. This can be accompanied by frost forming on the outside.
Hoarfrost	Ice crystals forming on a cold surface, from water vapour (skipping the liquid phase).  When there is enough moisture in the air, hoarfrost may form on any cold surface such as wires, poles, tree branches, plant stems and leaf edges. Even snow. Ice crystal ‘leaves’ typically form in the morning after a clear cold night in which the water vapour freezes on contact with a cold surface. Hoar frost can form as plates/flakes, ‘leaves’ or ‘ferns’ or as ‘needles’ depending on conditions. I’ve noticed the plates forming as irregular hexagons with three long and three short facets to form a triangular form.
Surface Hoar	Ice crystals that form on snow banks, usually over a clear cold night. The sparkles you see in a field of snow are reflections off the facets of surface hoar crystals. Surface hoar forms when a snowbank warms during the day and then cools overnight. As the surface of a snowfield rapidly cools, the interior ends up warmer than the exterior. This heat radiates out along with humidity from melting snow, and the moisture then contributes to the growth of the frost. Water evaporates from inside the snowbank and recrystallizes on the surface. By morning, the snowbank is covered with a layer of ice crystals. Best seen in the morning.
Frost Flowers	Also called ‘feather frost’, these typically look like cotton candy, several centimeters across, made of clusters of thin, curved ice filaments. They often form on water-logged wood. The ice filaments are pushed out from the pores of the wood as it freezes.
Rime Formations	During a freezing fog, when water droplets become supercooled, droplets freeze on contact, sometimes yielding bizarre, wind-driven shapes. Rime resembles hoarfrost but is thicker and longer, often forming long spikes during a low wind or thick coating if windy.

When air temperature is -12°C to -18°C, large fluffy dendrites can form. Dendrite snow has a snow to water ratio of at least 20:1. Skiers call this champagne powder and it’s the kind of snow they covet for its playful fluffiness. If the air temperatures are colder or warmer, more dense snowfall in the form of plates, columns or needles form. Nordic skiers prefer this denser snow.

Very cold air holds very little water vapour and is therefore less likely to produce snow. In the north, very light snowflakes called diamond dust can form in a cloud-free but very cold sky. The snowflakes form directly from water vapour, called desublimation (sublimation describes the opposite process, when snow turns directly into water vapour as opposed to melting into water).

The Snowflake

As a child, I marveled at the snowflake. I discerned even then that most snowflakes had a six-fold radial symmetry that displayed an elaborate and unique pattern. Foreshadowing my later scientific pursuits, I tried to classify them by shape and size. I intuitively realized that snowflakes looked different under different conditions of temperature, humidity and wind. Their type and size depends on the humidity and temperature present when they form. That’s why the flakes are small when it is very cold and they get larger when it’s closer to zero degrees Centigrade. Snowflakes are single or groups of crystals of pure ice. They grow from frozen water droplets (in the form of water vapour as opposed to much larger raindrops). Water vapour in the air condenses and freezes to add more ice to the newly born snowflake. Snowflakes have six sides because a water molecule lines up that way, based on its tetrahedral arrangement. While snowflakes are completely symmetrical with themselves, they don’t match any other snowflake. They are fractal.

How the Snowflake Forms

It starts with a dust grain or other foreign particle on which water vapor in the air sticks and forms an ice crystal with six facets. A cavity forms in each prism face because ice grows fastest at the edge. Six branches sprout and form corners of a hexagon. When the temperature cools to -13°C, growth at the branch tips narrow and at -14°C side branches sprout. More side branches sprout with fluctuating colder and warmer air, creating a fern-like fractal arrangement of branches. The fractal snowflake emerges.

While no two snowflakes look alike, you can still recognize types of shapes. Just as aggregated snow varies according to temperature and humidity, so do individual snowflakes. The snowflake starts out as a simple prism, with hexagonal faces. They are usually too small to see with the naked eye. As the snowflake grows and changes during the course of its travel to the Earth, its shape and size also changes.

Kenneth Libbrecht at Caltech tells us that “most photogenic stellar snow crystals grow in a narrow temperature range around -15°C. Needles and columns are best found around -6°C. Capped columns appear when the temperature changes as the crystals grow. Remember these are temperatures in the clouds; it is often substantially warmer on the ground.”

Types of Snowflakes

In 1951, the International Commission on Snow and Ice produced a simple and widely used classification system for solid precipitation. This system defined seven principal snow crystal types: plates, stellar crystals, columns, needles, spatial dendrites, capped columns, and irregular forms. Three additional types of frozen precipitation were included: graupel, ice pellets, and hail. In 1966, meteorologists Magono and Lee further elaborated (using physicist Ukichiro Nakaya’s systematic classification) and came up with eighty different snow crystal types. The chart below shows how the main forms of snowflake form over varying humidity and temperature.

Stellar or Sectored Plates are thin, plate-like crystals with six broad arms that form a star-like shape. Their faces are often decorated with elaborate and symmetrical markings; these divide the plate-like arms into sectors. Plate-like snowflakes form when the temperature is near -2 °C or near -15 °C.

Stellar Dendrites or ice ferns are the classic snowflake and the shape most of us imagine for a snowflake. It’s a “plate” snowflake that looks like a star or flower, with small side branches crystallizing from each of the six main branches. Some dendrites display a more intricate fractal arrangement, resembling a fern. Dendrites form in a wide temperature range, depending on saturation of the cloud, from just below freezing (low saturation) to minus 20°C (high saturation).

Fernlike Stellar Dendrites are larger and leafier than stellar dendrites and have many sidebranches, resembling a fern. They are often not symmetrical, the sidebranch of arms often randomly positioned, due to the rapidity of growth. These flakes grow to 5mm in diameter.

Columns and Needles are snow crystals, still with six sides, but in the shape of long “columns” or needles. Resembling pencils, they fall when the temperature is just below freezing, from around minus 5°C to minus 10°C). On one mild winter day in Toronto, nothing but these needles dropped from the sky, covering everything from my coat to my car with white “hair clippings.” This kind of snow is quite fluffy and develops when the cold air is more dry.

Capped columns form when the weather is a little warmer. Capped columns are basically six-sided columns with two plates on their ends like two wheels on an axle. I’ve also seen these, when they landed on my black car. They resemble an empty spool and form in minus 6°C to minus 15°C. They often accompany regular flakes in a mix of precipitation.

Diamond Dust Crystals are tiny snow crystals (no wider than a human hair), still in the hexagonal prism form, that form in bitter cold weather. They look like sparkling dust in the sunlight.

Triangular Crystals are truncated triangles that form presumably through unique aerodynamics. They still have six sides but three are stunted. The shorter sides may also sprout side branches, creating some unusual symmetry.

Rimed Snowflakes and Graupel are partially or completely coated in tiny frozen water droplets called rime. Rime forms on a snowflake when it passes through a super-cooled cloud. Blobs of rime form graupel or soft hail. Like hoarfrost, rime also forms on other cold surfaces (such as plants, branches, fence posts), often during a freezing fog.

Types of snowfall:

• A blizzard is a violent winter storm, lasting at least three hours, which combines subfreezing temperatures and very strong wind laden with blowing snow that reduces visibility to less than 0.40 kilometers (0.25 miles).
• A snowstorm features large amounts of snowfall.
• A snow flurry is snow that falls for short durations and with varying intensity; flurries usually produce little accumulation.
• A snow squall is a brief, but intense snowfall that greatly reduces visibility and which is often accompanied by strong winds.
• A snowburst is a very intense shower of snow, often of short duration, that greatly restricts visibility and produces periods of rapid snow accumulation.
• Blowing snow describes airborne snow particles raised by the wind to moderate or great heights above the ground; the horizontal visibility at eye level is generally very poor.
• Drifting snow is snow on the ground that is blown by the wind to a height of no more than 1.8 m.

Be Equipped for Snow & Cold

Part of enjoying winter is ensuring that I’m equipped to handle the biting cold (up to minus 30° C), chill winds and deep snow conditions. That includes sturdy snow boots, weather pants, a hooded warm parka, scarf, Moreno wool toque and warm mitts. I actually wear mitt-gloves so I can work my camera without taking them off. I even provide my camera with its own toque for warmth. On some days, when I know I will be braving fresh deep snow, I bring my snowshoes. For icy days (when the snow melts then refreezes) I keep my crampons handy. I always take something with me—a clementine or thermos of hot tea—to sustain my hours of adventure.

Glossary of Snow Formations

• Cornice is an overhanging accumulation of ice and wind-blown snow, characteristically found on the edge of a ridge or cliff face.
• Crust is a hard snow surface lying upon a softer layer, formed by sun, rain, or wind.
• Firn is old snow that has recrystallized into a dense material. Unlike ordinary snow, the particles are to some extent joined; unlike ice, the air spaces in it still connect with each other.
• Firnspiegel (German) when old recrystallized snow forms a glass-like surface on the snow field.
• Megadunes are giant dunes of snow in Antarctica composed of large snow crystals measuring up to 2 centimeters (3/4 inch) across.
• Penitents are tall, thin, closely-spaced pinnacles of hardened snow ranging in height from a few centimeters to a few meters (a few inches to a few feet). Fields of penitents can develop over glaciated and snow-covered areas, particularly in arid regions, such as the Dry Andes or in the mountains surrounding Death Valley in California.
• Ripple marks refer to the corrugation on a snow surface caused by wind, similar to the ripples sometimes seen in sand.
• Sastrugi are frozen wind-sculpted snow features. They occur when wind erodes or deposits snow in irregular grooves and ridges. In some vast open areas, the wind will sculpt a frozen sea of irregular ridges and grooves up to a metre high.
• Snow barchan is horseshoe-shaped snowdrift, with the ends pointing downwind.
• Snow bridge is an arch formed by snow that has drifted across a crevasse, forming first a cornice, and ultimately a covering which may completely obscure the crevasse.
• Snow roller is a rare formation that occurs during specific meteorological conditions. Wind blows a chunk of snow along the ground, and the resulting snowball accumulates material as it rolls along. Snow rollers are cylindrical rather than circular. Some are shaped like donuts because the weak inner layers collapse and blow away.
• Sun cups refer to a pattern of shallow, bowl-shaped hollows that form during intense sunshine.

Reference: NSIDC, 2020.

References:

Libbrecht, Kenneth. 2009. “The Secret Life of a Snowflake.” Voyageur Press. Minneapolis, MN. 48pp.

Libbrecht, Kenneth. 2015. “Snowflake Science.”

Libbrecht, Kenneth. 2015. “Guide to Snowflakes.”

Libbrecht, Kenneth. 2015. “Guide to Frost.”

Magono, C and C. W. Lee. 1966. “Meteorological Classification of Natural Snow Crystals”, Journal of the Faculty of Science, Hokkaido University.

Munteanu, Nina. 2016. “Water Is… The Meaning of Water.” Pixl Press, Vancouver. 586pp.

Nakaya, U. 1954. “Snow Crystals: Natural and Artificial” Harvard University Press.

NSIDC (National Snow & Ice Data Center). 2020. “All About Snow.”

Sheppard, Lola and Mason White. 2017. “Many Norths: Spatial Practice in a Polar Territory.” Actar Publications. New York, NY. 471pp.

Silgalis, Alex. 2020. “For the Chionophiles—Types of Snow for Skiing & Snowboarding.” March 24, 2020.