Wondering why it’s been so warm this week? You’re not alone.
While pretty much everyone loves a bit of sunshine and a bit of warmth, it’s hard not to feel a bit suspicious about the fact that it’s hotter now than it’s been for weeks.
And, although it was (alarmingly) the hottest Northern Hemisphere summer ever recorded, according to the World Meteorological Organisation, the UK was overcast and grey for much of August.
So why has it suddenly all changed?
Well, it comes down to a weather phenomenon called an omega block.
While yes, climate change is, of course, exacerbating these weather conditions, and the UK does regularly experience warm Septembers, the omega block is what is directly behind the 30C weather we’re enjoying right now.
What you need to know about an omega block
This is a weather block which is shaped much like the Greek letter of omega (Ω).
Weather front usually bring rain from west to east across the UK, propelled by the jet stream, the strong winds high above the Earth.
However, a block (like an omega) can disrupt this.
As the Met Office explained: “This just means that a big area of high pressure is remaining almost stationary over the same area for a long time.
“The high pressure can stop weather fronts moving past it, so that they skirt around the edges, or stay where they are for an extended period.”
At the moment, high pressure just to the east of the UK and centred over Scandinavia means hot and humid air from the south can sweep in and hover over the country.
Higher pressure means warmer and more settled conditions normally.
But, the block means there’s more unsettled weather on either side of the UK.
At the moment, there’s a tropical storm looming in the North Atlantic and storms in Europe, which has pushed the jet stream down – causing the omega shape.
Blocks can also create a heat dome, where high pressure stops it hot air from escaping, meaning it sinks, warming the ground, and in turn heating up the environment.
The block could linger for an indefinite amount of time
Weather blocks can hang about for anywhere between a few days to a few months. Once they’re established, they’re pretty hard to move.
The Met Office noted: “Exceptionally they can persist for months around mid-summer, like in 1976, or mid-winter, like in 1963.”
The UK is no stranger to having a warm September, although it’s only gone above 30C a few times. So far this year, the highest temperature is 32.2C – and forecasters expect it stay above 20C at night in many areas.
But thundery downpours will move in from the west on Wednesday, according to Sky News.
Why we might be experiencing more of these in the years to come
Sky weather producer Kirsty McCabe told Sky News that blocked weather patterns “seem to be happening more frequently in recent decades, and that could be linked to the effects of climate change on the jet stream.”
She added that the jet stream which flows over the UK may be changing because there’s less of a temperature contrast between the Earth’s equator and the Arctic.
The jet stream is driven by temperature difference. If the stream flow breaks, an area “can become separated and almost break off, taking low pressure with it and weakening its west to east movement’, the Met Office said.