Snow usually begins its life as crystals resembling hexagonal prisms, and thus, the hexagonal prism acts as the basic snowflake shape. As snowflakes develop, however, their shapes become more elegant and more flamboyant. This flamboyancy occurs as the prism and their sister basal surfaces slowly grow to their potential. Nonetheless, despite all their beauty, snowflakes would not be able to form and snow would not be able to fall if there were no such thing as evaporating water.
Water vapor comes from a variety of sources including lakes, rivers, oceans, plants, and moisture from exhaling animals. As these sources emit water vapor, or molecules, the molecules make their way into the air.
Molecules do not hang around in the air doing nothing however, and thus, when the air cools, the molecules begin to condense or make their escape from the air.
Appearing in two different levels – low-level and high-level – escaped molecules act in unique manners. Low-level molecules condense onto the ground, automobiles, leaves, and so forth. Higher-level molecules condense onto tiny objects such as dust particles. When molecules condense onto dust particles, they form water droplets and the water droplets eventually become clouds.
During cold weather, water droplets begin to cool inside clouds that cool as the weather changes. As clouds get colder, they begin to freeze. At length, clouds reach the freezing point (32 degrees Fahrenheit) and some of the water droplets inside the clouds freeze, or condense, into small particles of ice. When this happens, additional water vapor attaches to the frozen ice droplets and the droplets grow into basic snowflakes, also called snow crystals. Once basic snow crystals form, additional water molecules, floating or diffusing through the air, attach themselves to the basic crystals.
Most basic snow crystals have hexagonal prism shapes in that two of their sides, the upper and lower, consist of hexagonal shapes while their surrounding areas consist of six rectangular shapes. However, some snow crystals have flat plane shapes and others have long columnar shapes.
As water molecules make their way through the air in search of snow crystals to attach themselves to, the molecules become smaller. The overall size decrease, in the end, depends on how far the molecules must travel to reach the crystals. The farther they travel the more size reduction they undergo.
An important fact about what happens when basic crystals form, is that their developing shapes tend to be imperfect. These imperfections appear as inward dents or outward projections. When dents appear, water molecules must travel farther to reach dented snow crystal areas. When projections appear, water molecules do not have to travel as far. Variations in travel distance determine the size decreases molecules undergo as they diffuse, and thus, determine their appearance once they attach themselves to snow crystals. The appearance of consecutive molecules attaching themselves to snow crystals aids in the formation of each snowflake’s shape.
What tends to happen when snow crystals contain projections is that water molecules begin to attach themselves to crystals with increasing speed. This is because every time a molecule attaches itself to a crystal it decreases the distance the next molecule must travel in order to attach itself to the same crystal. This is sort of like stacking blocks from the floor while standing up. Every time you place a block on the stack, the stack grows closer to your hand until eventually you do not need to bend over to place another block.
When you do not need to bend over to place blocks on the growing block tower, you can stack blocks faster because you save time by not having to bend over. The same principle applies when water molecules do not have to travel as far to reach growing crystal protrusions.
In addition to snow crystals forming projections as they grow, water molecules attaching themselves to projections may create bumps or nodes. When this happens, upcoming water molecules can attach themselves to the “nodes” on the growing snowflake “branches”. This allows snowflake protrusions to grow in different directions, sort of like a tree. Only instead of growing from the base, or trunk of the tree, snowflakes form by attaching themselves to the outside of their base – their snow crystal.