Met Office urges caution over reports of '15-day snow bomb'
The weather service has said it is too early to confirm how significant the effects of an expected Sudden Stratospheric Warming will be.
The Met Office has played down reports of a "15-day snow bomb" hitting the UK in the coming weeks, but confirmed a potential Sudden Stratospheric Warming (SSW) weather event could take place in the next few days.
An SSW refers to a rapid warming of temperatures about 50km high up in the Earth's stratosphere. According to the weather service, while this can bring colder and drier weather, it is too early to say how severe any impact could be on this occasion.
A Met Office forecaster told Yahoo UK: “Models are indicating there could be one (SSW) on 4 or 5 January. But it’s too early to give any real details and we have to wait to see if one actually happens. If it does then we would possibly see the effects towards the end of January.”
Some of the recent extreme cold and winter snow events have been attributed to sudden stratospheric warming, such as 2018's 'beast from the east'. That weather pattern hit the UK in February and brought gusts of up to 70mph and temperatures of -14C recorded in parts of Scotland. More than 22 inches of snow fell in parts of the country causing widespread travel chaos, while the severe weather claimed the lives of 17 people, including a seven-year-old girl.
How does an SSW occur?
Sudden stratospheric warming (SSW) occurs when there is a rapid warming high up in the stratosphere, which can result in changes in surface weather. The warming, which can be as much as 50C in just a couple of days, occurs between 10 km and 50 km above the earth's surface in the stratosphere. Although we do not experience this warming ourselves due to how high up it is, its knock-on effects on the jet stream can be seen in a few weeks, which in turn affects the weather in the troposphere - the lowest layer of Earth's atmosphere.
During winter, a strong polar vortex of westerly winds circles around the pole in the stratosphere, high above the Arctic. Sometimes the winds of this vortex weaken or even reverse to flow from east to west. When this happens, the cold air from the vortex descends rapidly, causing a sudden rise in the stratospheric temperature of up to 50C in just a few days.
The dispersal of cold air from the stratosphere can impact the jet stream's shape as the cold air sinks into the troposphere. This change in the jet stream frequently leads to weather changes.
Storm Gerrit warnings
While next month's potential weather extremes are yet to become clear, Britons spent the period between Christmas and New Year dealing with travel chaos caused by Storm Gerrit. Travellers were warned of delays and potentially hazardous conditions on their way home from the Christmas holidays, with the storm forecast to bring wintry weather.
Wind warnings were in place for the south of England and across the English Channel coast as well as parts of western Wales, north-west England, Northern Ireland, northern Scotland and the northern isles. According to the Environment Agency, five flood warning - meaning flooding is expected - were active in England, along with 100 lesser flood alerts.
As a result of severe weather, British Airways cancelled 18 domestic flights, and LNER advised its customers not to travel. Network Rail Scotland also implemented speed restrictions, and travellers were urged to check for cancellations.
Flooding between Lockerbie in Dumfries and Galloway and Carlisle in Cumbria blocked all lines, according to Network Rail, and strong winds also led to the closure of the M48 Severn Bridge in Gloucestershire in both directions, as confirmed by National Highways.
Drivers were also facing problems, with several roads shut and the RAC cautioning them about the risks of high winds. The weather has led the RNLI to advise those visiting the coast to be extremely careful, especially along exposed cliffs, seafronts, and piers.
