Met Office explains what a Sudden Stratospheric Warming is
We use your sign-up to provide content in ways you’ve consented to and to improve our understanding of you. This may include adverts from us and 3rd parties based on our understanding. You can unsubscribe at any time. More info
The nation is hanging in limbo as to whether or not a sub-zero freeze is coming in March. A weather event, chracterised as sudden stratospheric warming (SSW), is currently taking place – and it initially contributed to the chaotic Beast from the East of 2018 which saw deadly weather conditions, including heavy snow, reach Britain. But forecasters are quick to remind concerned people that SSW also took place in 2019 – and had little effect on the mercury.
So what will trigger a second beast’s arrival in Britain? Express.co.uk can reveal a timeline of how experts will come to this conclusion – and there isn’t too long to wait.
What is sudden stratospheric warming and why do we care about it?
The meteorological jargon leaves little to the imagination of those who try and decipher its meaning. It actually refers to the warming of the stratopshere – an event which can take place at this time of year near Scandinavia.
The warming happens so high up that it’s never felt on the ground, and it’s full wrath is never guaranteed until weeks afterwards. What happens is strong westerly winds circle around the pole high up in the stratosphere. This is named the stratospheric polar vortex and it circulates around cold air high over the Arctic, the Met Office says.
Sometimes the polar vortext can weaken, collapse or reverse – which is what happened last month. But a second warming is already underway, and it has been dubbed as “major” by forecasters who are waiting expectantly to see what it means for Britain. It can take between two to three weeks for the full extent of its wrath to become known.
The Met Office’s explanation of SSW says: “As the cold air from high up in the stratosphere disperses, it can affect the shape of the jet stream as the cold air sinks from the stratosphere into the troposphere. It is this change in the jet stream that causes our weather to change.”
At the moment, the leading forecaster is looking at the last days of February and early March as a timeframe of when potential ice and snow could arrive in the UK. But the severity is not yet known – and may not be for at least another week.
“This blocking high pressure can lead to cold, dry weather in the north of Europe, including the UK, with mild, wet and windy conditions more likely for southern areas of the continent,” the Met Office said in its latest blog.
“However, this is not always the case and impacts on UK weather can also be benign when an SSW occurs.”
The Met Office also cited the Madden Julian Oscillation which is characterised by “enhanced and suppressed tropical rainfall” coming across from the east, as being a factor which is pointing towards a “favoured cooler spell in late February.”
What do we know so far?
Currently long-range forecasts remain extremely vague – but they do lean towards a risk of cold and wintry showers in early March. Netweather’s Jo Farrow said the SSW will have unfolded by February 16 – just two days time. This suggests more clarity may be given by the end of this week.
Ms Farrow said in a new update published today: “The answer to the question still remains and we don’t know yet. By Thursday, February 16 we should have seen the SSW taking place.
“We then wait a week or so to see how the forecast settles after such a major atmospheric happening and it will be eyes peeled for any signs of the deep blue colours on the thickness charts showing bitter cold marching eastwards at the surface.”
Meanwhile, the Met Office long-range forecast from February 28 to March 14 does not deny chances of a cold snap. It says: “The end of February is likely to see a continuation of changeable conditions, with the wettest and windiest weather most probable across the northwest.
“The south and east may see some shorter spells of wet weather, although overall conditions should remain drier and more settled. Into March, high pressure is expected to develop to the north of the UK and low pressure to the south.
“This is likely to introduce a north-south split, with drier conditions across the north and wetter conditions in the south.
“Temperatures expected to be mostly around average, but a period of colder or much colder temperatures remains a small possibility and could bring spells of wintry weather.”
Source: Read Full Article