No two are alike: The intricate science of snow crystals

By Brett Peto, Environmental Communications Specialist at the Lake County Forest Preserves, supplied by Kim Mikus.

Imagine you’re floating at the top of a cloud and you’re made of a dust particle. It’s 5 degrees Fahrenheit. Water vapor freezes onto you, making an icy, three-dimensional prism. It has six flat sides that form a hexagon. You’re now a snow crystal, commonly known as a snowflake.

Vapor attaches more easily to uneven areas than smooth areas. It sticks to your corners, which jut out a bit. Like spokes on a wheel, branches grow away from your center seed crystal, forming a starlike pattern. They develop independently. Like siblings, they have symmetry, but they’re not identical.

As you dance toward Earth through the cloud, these branches can split into smaller side-branches, making you look like a tiny, delicate ice flower. Different air pockets bring varying temperatures and humidity levels, influencing how vapor continues to freeze. Flat shapes, or plates, might grow at the tips and edges of the branches. Or the tips could become pointy, like needles.

The gathering weight causes you to tumble and emerge from the base of the cloud. You likely measure 0.05-0.2 inches in diameter, between the size of a grain of sand and a grain of rice.

During your descent to the ground, which takes 30-60 minutes, some branches may melt slightly.

You might collide with another six-branched snowflake to create a 12-branched pair. You could clump up with hundreds or thousands of other snowflakes. Or you could fall on your own, land on someone’s sleeve and catch their attention and awe.

Crystals from the clouds

The word “snowflake” has two meanings. It can refer to one ice crystal with six sides. It can also refer to a clump of hundreds or thousands of individual crystals. Picture a snowstorm with large flakes the size of pennies or nickels. Scientists use “snow crystal” to mean one ice crystal with six sides. It’s more precise.

“A snow crystal forms in a cloud when water vapor converts directly into ice without making a pit stop at its liquid form,” said Jen Berlinghof, environmental educator with the Lake County Forest Preserves. This process is known as deposition. “Each crystal takes a unique path, resulting in a one-of-a-kind snow crystal every time.”

Clouds are made of ice crystals, water vapor and droplets. Though there are exceptions, meteorologists generally group clouds based on how high their bases scoot through the atmosphere. Low clouds hang less than 6,500 feet, or 1.2 miles, above the ground. Midlevel clouds hover between 6,500-20,000 feet, or 1.2-3.8 miles. High clouds cruise above 20,000 feet, or 3.8 miles.

Nimbostratus and altostratus clouds are midlevel and produce continuous, moderate amounts of snow. Cumulonimbus clouds, whose bases are low but whose tops often reach the upper limit of the troposphere, produce heavy snow. The troposphere is the lowest layer of the atmosphere. Depending on the location, it’s between 26,000-47,000 feet, or 5-9 miles, thick.

Cumulonimbus clouds sometimes create thundersnow, a rare phenomenon that acts like a thunderstorm but involves cold, dense air moving strongly upward instead of warm, moist air.

It takes 15 minutes on average for a snow crystal to take shape. Clouds with lower humidity often yield thin, flat plates that grow slowly. Higher humidity spawns ornate, branched crystals that grow faster.

“Like a tree’s rings that tell the story of what was happening in the forest with each layer of growth, snow crystals grow from the inside out,” Berlinghof said. “Each new branch or plate tells the story of the cloud conditions.”

Photographing fragile snow crystals

How do you capture an image of something as delicate and fleeting as a snow crystal? R. Scott McNeill, volunteer photographer for the Forest Preserves, uses a black hat, a garbage can and plenty of hand warmers.

During snowfall, he bundles up, places the can outside his garage and rests the hat on top.

The hat has pronounced fibers, “so when a snowflake falls, it sits on top of the fibers as opposed to lying flat,” McNeill said. “This gives it a three-dimensional look.”

Speed is essential. The Lake County resident forgoes a tripod and instead leans against his garage door. “Snowflakes are very light … You find one and think, ‘Oh, this one is really cool,’ and next thing it blows away.”

McNeill uses a Canon R5 or R6 mirrorless camera, equipped with a 100 mm macro lens, an adjustable ring light and two extension tubes.

“The extension tubes take the lens farther away from the sensor in the camera, and that makes for a bigger snowflake when I look through the viewfinder.”

It’s tricky to take a single photo with every part of the crystal in focus. McNeill takes bursts of photos, minutely rocking the camera back and forth.

Using software, “I can take those images and stack them to try to get a more focused snowflake.”

He captures thousands of images per hour. In post-processing, he removes the hat’s fibers, darkens the background and reduces visual noise. It can take four hours of editing to create one finished product.

Snow-cabulary

Branch: A main arm of a snow crystal; grows from a corner of a seed crystal

Needle: Slender, pointy ice structure

Plate: Thin, flat ice structure

Seed crystal: Simple, six-sided ice prism; building block for more complex snow crystals

Side-branch: Smaller branch that splits off a main branch, like a twig splitting off a tree branch

Snow crystal: Single, six-sided ice crystal; contains a seed crystal