What is an ‘Omega block’ and why does Britain need one for a hot summer?

Paddle boarders on Lake Windermere in Cumbria. Picture date: Wednesday June 5, 2024. (Photo by Danny Lawson/PA Images via Getty Images)
The start of the summer has been distinctly cool (Photo by Danny Lawson/PA Images via Getty Images)

It’s been a distinctly chilly and damp summer this year, with many Brits complaining that summer has yet to start as we move into the second half of June.

But one forecaster has suggested that this summer’s dismal weather needs one thing to happen to bring about a prolonged warm spell - an ‘omega block’.

The reason for this summer’s grim weather is a polar airflow - a result of the polar front jet stream - a 30,000-foot-high airstream where cold Arctic air meets warm tropical air. At present, it’s below us, so Britain is being hit with colder Arctic air while other countries such as Greece are experiencing heatwaves.

The UK experienced its coolest first 10 days of June since 2020, in contrast to the hottest June on record, seen this time last year, when the mercury rose as high as 32.2C in Lincolnshire and Surrey.

But an ‘omega block’ could make all the difference, according to Joanna Donnelly of Met Éireann.

Despite sounding like a magic weapon that might be wielded by a Marvel character, an 'omega block' is a stationary area of high pressure over Britain.

High pressure is generally linked to warmer, settled weather.

There are several kinds of blocks, which remain nearly stationary and prevent the usual progression of pressure systems.

An 'omega block' resembles the Greek letter omega, and sees an area of high pressure 'stick' over Britain (Met Office)
An 'omega block' resembles the Greek letter omega, and sees an area of high pressure 'stick' over Britain (Met Office)

Omega blocks resemble the Greek letter Omega, with an area of high pressure over Britain in between areas of low pressure.

The Met Office said: "Omega blocks are named due to the pattern they form which resembles the uppercase Greek letter omega, Ω.

"An area of high pressure will be sandwiched in between two lows to the east and west, and also slightly to the south. These blocks frequently occur on the eastern edges of the Atlantic and eastern Pacific, and can lead to easterly flows to the UK."

Omega blocks can last for weeks or even months, and will see the area inside the ‘block’ remain hot and settled, while the areas around tend to be wetter, the Met Office says.

Joanna Donnelly of Met Éireann told the Irish Times that "there is no sign of a prolonged spell of good weather’ - and that we need the jet stream to move north of Britain.

She said: "The jet stream might move, it tends to move, but you cannot make it move.

"What we need is for the loops to get stuck. We call that an omega block, giving a period of prolonged high pressure.”

The Met Office has said that this week will start to see "more summer-like" weather, although there is still a chance for showers in some areas.

Brighter conditions will cover southern England for much of Monday and Tuesday where it will feel “much warmer than it did over the weekend”, but showers will still be possible across northern parts of the country and in Scotland and Northern Ireland.

A ridge of high pressure will initially bring cloud on Wednesday before thinning out for further brighter spells across the country, which will continue into Thursday for southern areas with light showers again likely further north.

More changeable weather will bring rain at times throughout Friday, with temperatures still “recovering” in the south to around average and still higher but more “subdued” further north.

Highs of 24C could be seen in south-east England on Monday, Thursday and Friday with low twenties possible on the other days.