UK weather: Another Beast from the East on the way?

14th January 2021 Last updated at 13:48
Ryhill, Wakefield
BBC
UK weather: Another Beast from the East on the way?

Meteorologists are keeping a close eye on events high in the earth's atmosphere, where something called a Sudden Stratospheric Warming - or SSW - has taken place.

This can have an effect on the weather we experience and bring cold spells.

What impacts will the SSW have on our weather in the coming weeks?

A major Sudden Stratospheric Warming (SSW) occurred over the Northern Hemisphere last week.

Temperatures in the stratosphere increased suddenly by around 45C over the space of a few days.

Temperatures began to recover at the end of the week but a second warming event is now underway.

The effects of an SSW do not always filter down to ground level and, even if they do, it can often take weeks.

While last week's major SSW did have some effect on a key player for extreme cold weather - the polar vortex - it didn't influence our experience at ground level.

The cold weather over the UK earlier this month was not at all related to the ongoing SSW.

BBC Weather's Ben Rich explains the phenomenon known as sudden stratospheric warming.

This second warming looks likely to be only a minor event in terms of temperature rise.

However, it could have greater impacts on our weather as the polar vortex has already weakened.

So forecasters feel it's more likely there will be outbreaks of cold weather in late January and early February.

Beast stays in the East?

A strong area of high pressure looks likely to become established across Greenland with the jet stream looping over it, allowing cold air to plunge southwards into northern Europe.

Jet stream winds and pressure pattern over the UK.
BBC
High pressure established over Greenland allowing cold air to plunge southwards into northern Europe.

The longer this pattern holds in places, the more extreme the cold pool of air becomes.

However, this cold pool is currently expected to be most intense across Northeast & East Europe with only occasional incursions westwards towards the UK.

Weather battleground

Although the overall pattern is expected to remain blocked for some time, there will be some degree of movement of the jet stream and so the UK is likely to find itself in the 'battleground' between the warm air to the west and the cold air to the east.

Air mass chart
BBC
Warm and cold air masses pushing across the UK

If the jet stream dives south to the west of the UK, we will be in a very cold northerly air stream and will see temperatures below average as we did in early January.

Some snow is also likely in this scenario. However, if the jet stream shifts to the east of us, we will be on the warm side of the jet with milder wetter conditions.

How long we spend either side of this jet remains to be seen.

Until the effects of the SSW actually filter down into the lower atmosphere, computer models will struggle to accurately predict our surface weather in the coming weeks. Even once this does happen, small errors in the forecast simulations could result in very different weather a few days ahead.

Therefore, while we are keeping a very close eye on the SSW and its possible downstream effects, it is far too early to predict any potential extreme weather for the UK.