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Wales Online
Wales Online
National
Angharad Thomas

Sudden Stratospheric Warming, a 'key step to Beast From the East', is underway

A weather forecaster says a sudden stratospheric warming (SSW), which could lead to another 'Beast from the East' hitting the UK, "looks to be underway". However, they say a deluge of snow is still far from certain.

A sudden stratospheric warming is often thought to lead to widespread snow and cold temperatures in the UK, but that's not always the case. For example, the one in February 2018 led to the Beast from the East, which covered large areas of Wales in snow and led to a rare red weather warning from the Met Office. But a similar event in January 2019 had no severe impact for the UK weather.

Sudden stratospheric warming is when a rapid warming occurs high up in the stratosphere, - the second layer of the atmosphere immediately above the troposphere. It refers to an area between 10km to 50km above the earth's surface and its effects are not usually felt until several weeks later.

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The Met Office has said that an SSW will impact weather in the UK at the end of the month. And BBC weatherman Derek Brockway tweeted on Wednesday: "A sudden stratospheric warming is underway. This increases the risk of a cold spell and snow late February into March but not guaranteed! Depends on the jet stream and where a blocking high pressure goes. The coldest air could miss the UK."

Derek then linked NetWeather where senior forecaster Jo Farrow wrote a detailed blog explaining the weather trend, saying that although sudden stratospheric warming was underway, another Beast from the East isn't a certain result by any means. Although it is a "key part" to significant temperature drops and snowfall in the UK, "there are a series of steps to get through in order to arrive at a Beast From The East setup where we might experience bitter cold and decent snowfall".

She continued: "Is there going to be a Beast from the East again this year? We don’t know yet, but a key step on the path to this type of cold, snowy setup looks to fall into place this week. That key step is... sudden stratospheric warming. However, without other steps, a Beast from the East won’t happen this winter. The warming occurred in 2019 but it did not result in a cold easterly setup. Overall, the end result of a Beast from the East is not that likely."

She added: "By Thursday, February 16, we should have seen the sudden stratospheric warming 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. If another very cold, snowy spell did seem likely for the UK, there would be time to highlight it and prepare. As there was in 2018."

There is currently a yellow weather warning for parts of the UK on Friday, February 17. Strong winds have been predicted by the Met Office for Scotland and the north-east of England, with warnings of danger from flying debris. The weather warning is in place from 6am on Friday until 6pm the same day.

The UK long range weather forecast from February 20 to March 1:

"Monday looks to be cloudy for most, with some brighter spells possible, these most likely to the east of high ground. Rain and drizzle across northern areas and western upslopes. Feeling fresh with moderate winds in the north, but light elsewhere and feeling mild. For the first half of the period, low pressure will dominate to the north and higher pressure to the south. This will lead to drier conditions in southern and eastern areas with some overnight mist and fog.

"More changeable, unsettled conditions with spells or rain and stronger winds at times are likely in the north. Towards the end of the period, there is a greater of high pressure dominating across the UK. Temperatures overall milder than average, but a continued risk of cold nights in places."

From March 1 to March 15:

"At the start of March, high pressure will likely dominate across the UK, with any more unsettled weather likely to be across the far north or northwest. Generally drier more settled conditions are expected, with occasional spells of unsettled weather possible at times, especially in the south. Cold nights are likely in places throughout the period. Temperatures will likely be around or slightly above average for the whole period, with perhaps colder conditions relative to average more likely later in the period. There remains a small probability of much colder weather developing as we move further into March."

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