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8 November 2016

Weak Polar Vortex Threatens to Bring a Freezing UK Winter

With all the warm autumn temperatures in the UK, you could be forgiven for getting a little complacent this winter, maybe not preparing the interior or exterior of your home for a cold one. Well, dig out the duvets and whip out your winter gear, as the Met Office’s latest 3 month forecast indicates that we could be in for a cold start to winter, with the cold snap that started this week marking the first time temperatures have consistently dipped below double digits. Not only that, but the chill could last the whole season, with the forecaster’s predictions showing a 30% elevated chance of a cold winter. Brrrr!

Though the Met Office are keen to stress that localised weather systems are only predictable up to 10 days in advance, they can use wider data to forecast more general trends for the season, and technology keeps developing. The most recent report covers November 2016 to January 2017, and forecasts the probability of certain levels of temperature and precipitation. The report indicates that the current outlook gives an overall 30% chance of the UK experiencing a ‘cold’ winter. This is one-and-a-half times the usual risk, so although it’s not categorically affirming the coming of the next Ice Age, the chance of a colder winter is definitely significant. This could of course change going forward as the weather signals used by the Met Office to make this prediction could change themselves.

So what exactly are the forecast signals that contribute to this prognosis? Well, there are two major forces that influence it. The first is the El Niño-Southern Oscillation (ENSO), the variation in temperatures over the tropical Pacific Ocean. This fluctuation affects the westerly winds that bring warm air to the UK, especially when El Niño’s cold counterpart, La Niña, takes over. La Niña can reduce the strength of these winds, meaning a colder winter, and El Niño has already dissipated in mid-summer this year.

The other main factor in the forecast is the stratospheric polar vortex. This isn’t a new theme park ride, but rather the wind system that whirls around the North Pole during winter. Every year it begins to strengthen through autumn as winter begins to set in, but this year that power surge has been much less notable than usual. The weak vortex means that cold air is no longer trapped at the North Pole and begins to creep down towards the landmasses of the northern hemisphere, the UK included.

The Met Office also uses computer simulations to predict other parts of potential weather systems surrounding the UK that may influence the long term forecast. For instance, they envisage high pressure systems to the northwest of the UK that may block incoming depressions, preventing milder weather systems from settling in.

It’s unlikely that the freezing winter will match that of December 2010, which was the coldest for 100 years, and the Met Office is keen to stress that their forecast only indicates an increased probability and not a concrete divination. Nevertheless, it serves as a good heads up for weather-dependent contingencies, such as stocking grit for the roads. It’s always best to be prepared, particularly if you work outside. Make sure the inside and outside of your home are ready and elderly relatives safe, and it’s never too late to get some insulation in now that the heating is switched on (maybe automatically).

However you decide to do it, make sure you keep yourself warm!

Sam Franklin

With a master’s in Literature, Sam inhales books and anything readable, spending his working hours reformulating the info he gathers into digestible articles. When not reading or writing, he likes to put his camera to work around the world, snapping street photography from Stockholm to Tokyo. Too much of this time spent in Japan teaching English has nurtured a weakness for sashimi, Japanese whisky, and robot cafés.