A Sudden Stratospheric Warming (SSW) event has taken place, resulting in the split of polar vortex in two vortices which may impact our weather later this month (there is a lag time between an SSW and the impact it has on UK weather).
A SSW of the atmosphere refers to a rapid rise in temperatures in the stratosphere (which is found at an altitude of 10 km to 50 km) when the temperature can rise by up to 50°C over a couple of days – and this often leads to cold conditions across the UK.
Although SSWs don’t always result in cold snaps, there is a high potential for a cold spell across Europe towards the end of February, as the SSW event may result in easterly winds for western EU and the UK. These easterlies could alter the weather pattern, weakening areas of low pressure and shifting the jet stream further south, resulting in high pressure over the North Atlantic which ‘blocks’ the flow of mild Atlantic air and pulls down cold air from the north east. Once these high pressure systems are established, they can persist, leading to a protracted cold spell of up to 15 days. How cold and wintry it is in the UK will depend on precisely where the air originates from.
The last cold and snowy spell caused by a sudden stratospheric warming event was in March 2013. It lasted for about 15 days and bough the coldest weather since 1883. December 1981 was another time that sudden stratospheric warming bought a cold-weather event, with that December the coldest of the 20th Century.
The models are currently showing a strong signal for this cold weather set-up to occur at the surface by the end of this week. Met Office Chief Meteorologist Andy Page, said: “High pressure will become established across the UK by the middle of this week bringing settled weather for most, but also some frosty nights. However, as the high drifts east to be over Scandinavia by the weekend, it will allow colder air from Eastern Europe to be drawn towards us. The cold easterly wind will bring an element of wind chill which will make it feel colder in the south.”
So by Friday morning, temperatures will be several degrees cooler than average. There will be widespread frosts with temperatures around -3°C, with rural spots dipping lower. Some places will struggle to rise above freezing during the day with the cold easterly wind - the 'Beast from the East' - making temperatures in the south and east of England feel even colder. However, there is still a question mark around the amount of snow we might receive. Whilst we need cold weather for snow, we also need moisture.
The latest forecast (21/02/18) from the Met Office states: "There is potential for some disruptive snowfall next week, although the likelihood of heavy snow in any given location is very difficult to gauge; some places could see some significant amounts of snow, while nearby locations may receive very little. At this stage, we consider the region’s most likely to have disruptive snowfall are parts of east and southeast England. Here, disruption to travel is possible for the start of the working week."
Watch this space for further updates!
To find out more about SSWs click here
Listen to the RMetS podcast discussing the 'Beast from the East':
Watch this Met Office video by Prof Adam Scaife, Head of Seasonal to Decadal Forecasting at the Met Office and member of the RMetS Climate Science Communication Group: