The weather phenomenon with the potential to bring a “Beast from the East” to the UK could already be underway, the Met Office has said.
It comes after a cold snap earlier in the week, which saw an Arctic airmass from Siberia bring snow and ice to Britain and temperatures of -12.6C in one area of Scotland on Thursday night.
Conditions may have turned milder over the weekend, but another blast of cold weather could be on its way due to a specific weather phenomenon, forecasters have suggested.
The Met Office told Yahoo News that “there are indications a minor sudden stratospheric warming (SSW) event is underway”, adding that it is “relatively early in the winter season for this to occur”.
This is the same phenomenon responsible for the Beast from the East that swept the UK, Ireland and much of continental Europe in 2018, bringing unusually low temperatures and heavy snowfall.
Contrary to its name, sudden stratospheric warming events are generally known to bring bitterly cold weather to the UK. Here’s how they work.
What is an sudden stratospheric warming?
Sudden stratospheric warming, or SSW, refers to the rapid warming of air in the stratosphere, which is between 10km and 50km in altitude.
This phenomenon can see temperatures soar to 50C in just a couple of days, the Met Office says. This heating-up happens so far above the Earth’s surface that we don’t feel the warming ourselves, but it does have a knock-on effect on weather closer to home.
Every winter, strong westerly winds circle around the Arctic high up in the stratosphere, in what is known as a stratospheric polar vortex, the forecasting service explains.
In some years, these winds temporarily weaken, or even reverse to flow from east to west. Cold air then rapidly descends in the vortex, causing the temperature in the stratosphere to rise rapidly.
“Fluctuations in our weather send waves up through the atmosphere to the easterly winds in the stratosphere, where they travel no further, and instead break and reinforce the easterly winds, bringing the easterlies lower,” the Met Office explains.
As this cold air disperses, it can affect the movement of the jet stream that affects our weather, bringing it further south, leading to higher pressure in the North Atlantic which blocks the flow of mild Atlantic air and drags in cold air from the continent.
How does it impact UK weather?
Depending on where you are in the world, the weather is likely to be affected differently by SSW events.
“The stratospheric sudden warming can sometimes cause the jet stream to ‘snake’ more, and this tends to create a large area of blocking high pressure,” the Met Office explains.
Typically, this high pressure will form over the North Atlantic and Scandinavia, meaning northern Europe, including the UK, is more likely to experience a long spell of dry and cold weather.
Snowy winds blow through Chard, Somerset during the Beast from the East phenomenon of 2018. (Alamy)
Meanwhile southern Europe tends to have more mild, wet and windy weather as a result of this phenomenon.
On the boundary of these areas, cold easterly winds develop and in some cases a drop of temperatures leads to snow, as seen during the so-called “Beast from the East” which swept Europe in early 2018.
How likely is a Beast from the East?
Firstly, it’s important to note that SSW events do not happen every year, and don’t always affect our weather.
However, the Met Office says that when these events occur, a “cold snap follows more often than not”, meaning they greatly increase the risk of wintry weather.
In a statement to Yahoo News, the forecaster said: “There are indications a minor sudden stratospheric warming (SSW) event is underway.
“While SSW events can happen in November, it is still relatively early in the winter season for this to occur.”
The Met Office said that it typically takes around 10 days to three weeks for the effects of an SSW to propagate downward into the troposphere and potentially influence the weather we experience.
“This means impacts would not be expected until early to mid-December and therefore it’s too early to provide definitive details on potential impacts for the UK at this stage,” it added.
“While this could suggest a cold start to winter some SSWs have little or no effect on UK weather, for example we saw a minor SSW in 2019 which had little effect on our weather.
“Around 70% of major SSWs are followed by colder conditions and easterly winds across northern Europe, including the UK, but not all events lead to severe cold or snow.”
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