Sudden stratospheric warming: What could it mean for the UK's weather this winter?
A rapid warming high above the Arctic can change where Britain’s winter weather comes from. It helped set the scene for the Beast from the East, but does it tell us anything about our chances of a white Christmas? Our weather expert Gareth Butterfield breaks it all down.
You're likely to start hearing a lot about a Sudden Stratospheric Warming in the coming weeks because there's a chance it's going to happen, but the question we're all going to be asking is: will it affect our weather this winter?
The short answer is... possibly. It's not a particularly rare occurrence, it's happened plenty of times before, and the way it affects the weather in the UK is as complicated as it is unpredictable.
In the past, Sudden Stratospheric Warmings have had a marked affect on UK winters, but they've also done absolutely nothing. However, with a "super El Nino" also making headlines this year many are saying we could be in for a bumpy ride.
What is a Sudden Stratospheric Warming?
A sudden stratospheric warming happens when the air high above the Arctic heats up rapidly, sometimes by tens of degrees in just a few days.
This can weaken or even reverse the strong winds that normally circle the pole in winter, disrupting what’s known as the polar vortex. You'll have heard of this in tabloid headlines, no doubt.
If the effects reach lower levels of the atmosphere, they can shift the jet stream, which is the ribbon of air that dictates so much of the British weather.
How does shifting the jet stream affect our weather?
One of the principle impacts the jet stream's position over the UK has is dictating where we source our weather from.
When it steers weather systems in from the Atlantic, we often get milder, wetter and windier conditions in winter. If its path shifts, it can open the door to colder air from the Arctic or continental Europe. Remember the "Beast from the East"? That happened because the jet stream shifted south and a blocking high developed over Scandinavia. And it followed a Sudden Stratospheric Warming.
So a jet stream that shifts south raises the chances of frost and, if there’s enough moisture in the air, snow. But a shift in the jet stream alone doesn’t guarantee a cold snap, which is why we need complex modelling to spot patterns emerging.
Is the Sudden Stratospheric Warming going to happen?
This is the important question. At the moment there's a fairly good likelihood, with models disagreeing on the detail, but mainly pointing towards at least a minor technical warming.
What will happen in the UK if it does develop?
At first, absolutely nothing, it'll be business as usual. Any knock-on effects on UK weather could take several weeks to emerge, if they do at all. It all depends on whether the disruption high above the Arctic changes the path of that jet stream.
That could make it easier for colder air to reach the UK, but it’s too early to say whether it will bring a cold snap, let alone snow.
It’s important to remember, there have been plenty of occasions there has been absolutely no effect in the UK.
Does the Sudden Stratospheric Warming mean we're going to get a white Christmas?
Funnily enough, it could increase the likelihood, if only by a little bit. And that’s if it even happens. But it's such a long way off, and there are so many other factors that can come in to play, anyone who forecasts a Dickensian scene on Christmas Day is being a little bit dishonest.