Will it snow this Christmas?

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Will it snow will it snow will it snow?

And who on earth might know?

Well it’s plain to see, that it won’t be me, for the future’s hard to tell (based on the statistical probability of a defined weather event occurring at a specific place and time due to the near impossibility of predicting the course of such a complex system dependent on impossible to measure initial conditions and highly susceptible to even the slightest permutations across a range of influencers). In other words, nobody knows, or nobody can know for sure, because sure cannot exist in the world of meteorology.

Why can’t we be sure?

It does seem a tad paradoxical that we are able to predict solar eclipses and alignments of the planets thousands of years into the future, yet here on this rock, with 106 million observations a day, the latest £97 million supercomputer capable of 16,000 trillion calculations per second and a four-day forecast as accurate as a one-day forecast 30 years ago, the Met Office still can’t be sure if it’ll be sunglasses or umbrellas most weekends (if in doubt, the latter). The explanation seems to lie in chaos theory, popularly referred to as the butterfly effect.

The basic assumption of the theory (and I won’t attempt to pretend I can go much beyond than that) proposes that in order to predict the future state of a complex system such as the weather, its current state must be known to a degree of zero uncertainty and the model describing it perfect. Even the slightest error in description or unaccounted-for disturbance (such as a butterfly flapping its wings in Australia) can snowball (intended!) into a vastly different evolution of the system and result in a snowy London on Christmas instead of sunshine (both unlikely).

In essence, what this means is that until we can model the exact condition of every particle within the atmosphere (and there are roughly 250 trillion trillion of them in a cubic meter of air – several times more than the number of stars in the observable universe, to give an idea of how many that is) as well as the influencers on the atmosphere such as water cycles, jet streams, cloud coverage, sunlight, pesky butterflies and much else, we we may never be able to predict the weather much further than two weeks in advance, and I don’t know if it’ll snow on Christmas.

What’s the forecast?

It won’t stop us trying however, and with its fundamental unpredictability established, we turn optimistically to our flawed though still remarkable Christmas weather forecast, followed by the bookies – who often hold insights beyond the limitations of science. At the time of writing, the forecast suggest there will be no snow over the festive period. A succession of Atlantic depressions are likely to bring heavy rain, winds and comparatively warm temperatures of around 10°C, possibly evolving into a storm, nicknamed Barbra. Not exactly festive, but anything is possible, so we look to an industry that thrives off its customers’ belief in exactly that.

What are the odds?

The Met Office defines a white Christmas as “a single snowflake falling during the 24 hours of Christmas Day”. With such a generous definition 38 of the last 54 Christmases can be said to be white. But most I believe, would define a truly white Christmas as widespread snow across the country, which accounts for only four out of the last 50, the last occurring in 2010. For 2016, it looks like Scotland and Aberdeen is the favourite at 9/4, Newcastle at 3/1, Liverpool the least likely at 11/2 and London at a respectable 7/2 (source: major betting company).

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