Nick on Snow

It is one of those extraordinary facts of nature we all learn at school that no two snowflakes look exactly the same. Perhaps less well known is the fact that the shape of a snowflake depends on the temperature of the air when it forms.

The classic star-like silhouette with six elaborate, symmetrical arms is formed at temperatures between -1°C and -3°C. When the temperature sinks to around -5°C, snowflakes look more like needles or narrow columns, but the hexagonal star shape returns again at -10°C.

Snowflakes are ice crystals, and the different shapes of ice crystals on the ground are important when it comes to avalanches. I hadn't fully realised the danger presented by avalanches in Britain before I filmed this series. But in the ski resorts and mountains of Scotland they take them very seriously.

There are several different types of avalanche, made up of loose snow, wet snow and slabs of snow. The slabs don't have to be very large to be fatal. People can die on a sliding slab just a few metres across.

In the Cairngorms in Scotland I experienced my first white-out. It is very disconcerting to stand in an atmosphere so thick with falling snow that you don't know which way is up. It feels strange and ghostly but also supremely disorienting. No horizon, no sense of distance, let alone direction. It is easy to understand how people lose their way very quickly.

Snow is two-faced. It can be fun and picturesque but, at the same time, bitterly cold and dangerous. It is beauty and the beast.

For most of us, however, it is perhaps best described as a nuisance. The Highways Agency spends more than £150 million each year gritting our roads against snow and ice. (Actually it is salt rather than grit, most of it dug from a single mine 500 metres below the Cheshire countryside). But a fall of snow, no matter how small, is still likely to cause chaos on the roads in Britain.

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