The Science Behind Snowflakes and Snow Crystals
Have you ever taken a really good look at individual snowflakes when you’ve been out while it’s snowing?
If so, you’ll have noticed that their appearance can vary from snowfall to snowfall. Sometimes snow comes down as beautiful tiny, lacy six-sided crystals, and sometimes it comes down in needle-like or columnar shapes, or most commonly as irregular shapes. Often snow will come down as clumps of snow crystals — that’s when we see the big puffy snow flakes.
Snowflakes start out as ice crystals that have formed around small bits of dust or dirt in the atmosphere.
The shapes that they take depend on the weather conditions, such as temperature, humidity (how much water vapor is in the air), wind speed, and how long it takes for them to fall to the ground.
What is a Snow Crystal? What is a Snowflake?
A snow crystal is a single crystal of ice, as shown in the examples on this page. The crystal may not necessarily be six-sided. It could be needle-shaped, columnar, or a twelve-sided crystal, or it could be quite irregular. You won’t see other types of symmetry, such as 5 or 7-sided flakes.
A snowflake is a more general name that can refer to one snow crystal, or a few crystals stuck together, or a large group of snow crystals grouped together as a snowflake puffball. There may be up to a couple hundred snow crystals in one large snowflake.
Photographic Print by K. LibbrechtAllPostersPhotographic Print by K. LibbrechtAllPostersPhotographic Print by K. LibbrechtAllPosters
The three images above, photographed by physicist, snowflake researcher and photographer, Kenneth Libbrecht, are beautiful examples of hexagonal (6-sided) snow crystals. The first one in particular is representative of the more familiar snowflakes that we see in drawings and decorative designs. Note the relative simplicity of the last image, although it’s still quite beautiful.
The four images below are also snow crystals but certainly not what we think of as the “picture book” snowflake. The last one is of irregular snow crystals, which are the most common kind. They’re usually clumped together and don’t show much symmetry.
The beautiful six-sided flakes are less common than non-hexagonal crystals, but more of what we’re used to seeing in popular depictions of snowflakes.
Non-hexagonal snow crystals. Images from SnowCrystals.com, a site by snowflake researcher and photographer Kenneth Libbrecht. Used in accordance to the copyright guidelines on this page.
See more photos and information on SnowCrystals.com.
Snowflakes Begin in Clouds
Snowflakes form in clouds when the temperature is too cold to form rain drops. Clouds consist of water vapor.
A very tiny ice crystal, or snow crystal, forms from water vapor condensing around a speck of dust or dirt in the atmosphere. As the snow crystal grows and gets heavier, it starts to fall earthward.
Along the way down it will encounter many different environmental conditions — it may grow more quickly or more slowly, or form different shapes depending on the conditions it goes through. It may also collide and combine with other snow crystals, forming bigger snowflakes.
“Nature is full of genius, full of the divinity; so that not a snowflake escapes its fashioning hand.”
~ Henry David Thoreau
How Do Six-Sided Snowflakes Form?
The six-sided shape comes from the configuration of water molecules, and how they interact with each other in a solid state (ice, snow).
A water molecule (below left) is made up of two Hydrogen atoms and one Oxygen atom (H2O).
In a solid state, water molecules form weak bonds (hydrogen bonds) with each other that pull them into a symmetrical hexagonal (6-fold) lattice shape. This is why you won’t see symmetrical snowflakes that are 4-sided, or 5- or 7-sided. You might see snowflakes that are 12-sided, since 12 is a multiple of 6.
Water molecule (left) and ice lattice made from water molecules.
But Are They Perfectly Symmetrical?
Some are pretty close!
It does look like the snowflake below is perfectly symmetrical, doesn’t it? But look very closely at the six arms, and you’ll notice that each arm is just a little different than the others. It’s like the Spot the Difference picture puzzles we looked at as children (and maybe still do!) — we’re shown a couple of drawings that at first glance look the same, but on closer inspection have tiny differences.
Some snow crystals, such as this one, are very nearly visually symmetrical, while others are much more noticeably unsymmetrical.
Photographic Print by K. LibbrechtAllPosters
What Determines the Shape and Pattern of a Snowflake / Snow Crystal?
The size and shape of a snowflake is determined in part by the temperature, humidity, and air currents in the zones that it falls through. Its formation and growth is dynamic and complex because it will fall through many different zones with different conditions before it lands. In some zones it might sprout dendrites (feathery branches), and in others it might start to melt, only to branch and grow again in different zones.
Snowflakes that spin like a top are more symmetrical than those that fall sideways. The amount of dust or dirt in the flake will affect its shape too.
Temperature is a big influence of the different shapes. At warmer temperatures, the shapes grow more slowly and are usually smoother. At colder temperatures the shapes can be more intricate. But humidity also plays a big part in the growth and shape of a snowflake. Higher humidity allows for more complex patterns.
Forms can include:
- Star-shaped
- Star-shaped with dentrites (feathery branches)
- Columnar-shaped
- Columnar-shaped with capped ends
- Needle-shaped
- Plate-shaped
- Irregular
…and more.
See a chart of different snow crystal shapes.
See a Snow Crystal Morphology Diagram, showing the different shapes expected at different temperatures.
Snowflakes on my windshield
The Main Sources I Used for This Page
- SnowCrystals.com
This is the best siteI’ve found to learn more about the science of snow crystals and snowflakes. - Snowflake Chemistry
Here are answers to common questions about snowflakes. Learn how snow forms, what shapes snowflakes take, why snow crystals are symmetrical, whether no two snowflakes really are alike, and why snow looks white. - Snowflakes from KidsWorld
Do you catch snowflakes with your tongue? Find out the ingredients in that snow and why you won’t find any two that look exactly alike.
Recommended Books to Learn More
Ken Libbrecht’s Field Guide to Snowflakes
The Snowflake: Winter’s Frozen Artistry
I hope you enjoyed learning more about snowflakes and snow crystals!