Since the rather wonderfully named Waterlooville, here in South England is currently under inches of snow, I thought I would write a blog about it!

A snowflake can be either a single ice crystal, two of them fused together, or a whole mass of them getting together to have a party, to make a kind of snowflake puff ball. Snowflakes are not frozen raindrops, that would be sleet. Instead they are crystals which form when water vapour condenses straight into ice in the clouds. The unique shape and pattern of each snow flake gradually emerges as the crystals grow.

A snow crystal, that may be round, will attract material to it, because it is rough, but then there may also be a number of facets that are smoother and so accumulate material much more slowly. After all the rough surfaces have grown out, only the slower-growing facet surfaces remain, to create the snowflake. A snowflake is, most commonly, a hexagonal prism in shape. This, in turn can either be plate-like (or flat), or columnar, depending on which facet surfaces grow the quickest.

When snow flakes are just baby flakes, they tend to just be these hexagonal prisms, but as they mature and grow, branches grow out from the corners to create more intricate and complex shapes. This perfection, is, like so many things in this world, created from imperfection. Snowflake branching occurs because in order for water vapour to attach to the ice crystal, it has to diffuse through the air. If it finds a spot on the crystal with a tiny protuberance, it does not have to travel so far through the air to condense, so it tends to concentrate itself around and grow quicker at that particular spot…creating a branch. Then that branch in turn may have minor imperfections, so the process repeats itself. The result is an exquisite structure…unique to itself, because no two ice crystals will have lumps and bumps in the same spot. Cool physics, huh?

Now for more interesting science! Thin plates and starlike flakes tend to develop at temperatures of -2º C (28 F) and -15º C (5º F),columns and needles at around -5º C (23º F) and a combination of plates and columns at about -30º C (22º F). Also snow crystals tend to form simpler shapes when the humidity is low, and more elaborate ones as the humidity rises.

So the life of a snowflake entails evaporation of the water vapour from seas, lakes, rivers, plants, even you, when you exhale! If you take that air and cool it down, it will eventually condense, as dew if it is near the ground, as snow, if it is way up high.Snow-forming clouds are just conglomerations of liquid water droplets, until the temperature drops to about -10º C (14º F) and then the droplets gradually start to freeze, as described above.

So the next time it snows, consider the complicated evolution of that single snowflake that lands on your hand!