Why does snow fall in such cool shapes?

We went to the snow last week! It took some effort and planning, taking two little dudes on a plane to the other end of the country (for those of you reading this from overseas, this flight only took an hour and a half, so don't be too impressed) and then getting them up and down mountains each day, but it was worth it. 

The two-year-old is now obsessed with mountains and snowboarding and keeps saying he wants to go back to "Keenstown". The 8-month-old was impressed for the first half hour of each trip up the mountain, then his mood generally deteriorated. Fair enough when nobody will put you down to crawl on that slippery white stuff and you're wearing a stuffy ski suit that makes you look like Maggie Simpson. How degrading!

In the flurry of planning and packing and traveling and recovering, this blog has been neglected. But here I am again, in sunnyrainy Auckland, where the winter never really happens, but where our lives do.

I can't say I saw it snow while we were in Queenstown. In fact, the weather was pretty warm the whole time we were there and the snow conditions were definitely Spring-like, with a good deal of slush at the end of each day. Despite not seeing a single snowflake land, I did get thinking about snowflake related questions, like today's Why.

Why do snowflakes make such awesome shapes?

Obviously, like other forms of precipitation, snow comes from the clouds. There is a whole lot of vapour up there milling around and eventually it needs to come down. The temperature needs to be below freezing for the vapour to form ice crystals, which will make up our beloved snowflakes.

Crystallization is one of those amazing things that happen on Earth, which remain amazing despite being explained by science. Like other crystals, ice crystals need a starting point to grow from. Often, this happens when cold water vapour hits and clings onto a dust particle, which can even be a bit of space dust. I always knew there was something mystical about snow.

Once the nucleus of the crystal has formed, the water molecules arrange themselves into an hexagonal shape, as this is the natural pattern created when you bond hydrogen and oxygen to make water.

As it falls towards the Earth, the ice crystal meets up with more cold water vapour, which attaches itself to the six sides, making the six crystalline arms you usually associate with snowflakes. Sometimes, these crystals attach themselves to other ones that are falling through the air at the same time, making the big, fat fluffy flakes I so miss from North America.

It needs to be below zero all the way down to the ground for the crystals to fall as snow, otherwise they may turn into hail or even rain.

Why is each snowflake unique?

The ice crystals grow and change as they fall through the atmosphere depending on the temperature and levels of humidity they encounter. Slight changes in temperature and humidity will distinctively change the shape of the crystal, so for this reason, with all the shifting air in the wintery sky, each snowflake is likely to form slightly differently.

Fun fact: the largest recorded snowflake was 38cm and fell in Fort Keough, Montana, USA in 1887. However, this was apparently observed by a farmer who described the flakes as 'larger than milk pans'. Sounds a bit dubious to me.