The calendar says it's summer – yet it's cold and rainy. Why?

Under the Microscope


Answered by: Sarah Grintzevitch, Royal Meteorological Society




Weather systems and the wind


All our weather in the UK is affected by the wind – the wind brings in our weather systems. And where the wind comes from affects whether it brings warm or cool air.

If it comes from the sea it collects moisture, which will then fall as rain. As you might expect, sea winds are wetter, whereas winds that come across land will be dryer.

At this time of year, we would normally expect a westerly or south-westerly wind, which brings daytime highs of 17C. But we've been having winds from the north, which have brought colder temperatures.

It's not that in the summer we don't get winds from the north, but as summer goes on the sea warms up, which means that the air warms up, making the north winds feel less cold. At the moment, the sun hasn't yet had a chance to warm the North Sea, so the air feels noticeably colder. At this time of year we would expect an average of 13C to 14C – which is being brought down by the wind to about 5C, which feels like a big drop. But in the summer, if it's 20C and a north wind brings it down to 15C, it doesn't feel as extreme.

Another example of wind bringing unusual weather is when it comes from across the Continent. In 2003, when we had a very hot summer, it was because we were getting winds from across Europe which warmed up as they crossed the land.

Air pressure

There are a lot of variants in the weather systems, but the main variant affecting the direction of the wind is air pressure.

Things like the intensity of the sun's radiation, the sea's surface temperature and the density of the air all in turn impact on atmospheric pressure.

And then what type of weather is brought by the different pressures depends on the time of year. At this time of year, and in summer, high pressure is likely to bring warm weather.

But during the winter months high pressure may bring unusually wet, mild weather. And there is what we call the North Atlantic Oscillation (NAO), which is the movement of the sea and atmospheric pressure between the Azores and Iceland.

It's a big factor in our weather in general, governing the air that flows into the UK. One pole of it is the Azores High, a high air-pressure system – a warm area of air – which we would like to have over the summer months to keep us nice and warm. However if we get winds from Iceland and the Arctic in the summer, then it will be cooler, and they also bring moisture so it's likely to be wetter. So a cold, wet summer may be caused by the other pole of the NAO, the Icelandic Low.

El Niño and La Niña

A factor which affects weather around the world is El Niño and La Niña. These are changes in the density of the Pacific Ocean, a change in the flow as it moves across from South America to Asia.

El Niño sees the Pacific warming, while its opposite, La Niña, sees it cooling. The flow of the ocean changes in that specific area in the Pacific, and the ocean very much changes what happens in the air.

So that single thing changes the weather across the world. During the Winter Olympics in Vancouver, they had hardly any snow because of the warming effect – which was unfortunate. Obviously the further away you go, the less effect there is.

Forecasting unseasonable weather

Weather is a bit like the chaos theory. With weather, there are so many small variables that can have an impact, and they can affect us so that we get snow in May, or a nice warm February. That's why forecasting isn't an exact science.

But the weather forecast is now pretty accurate in reporting unseasonable weather. The three-day forecast is now as accurate as the one-day forecast was 10 years ago. So all the cold weather we had before Christmas, and the cold weather over Easter – that was all forecast.

Send your science questions to microscope@independent.co.uk

Start your day with The Independent, sign up for daily news emails
ebooks
ebooksAn introduction to the ground rules of British democracy
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Technical Service Engineer - Vehicles

£25000 - £65000 per annum: Recruitment Genius: One of the UK's premier supplie...

Recruitment Genius: Home Care / Support Workers

£7 - £10 per hour: Recruitment Genius: This care provider is looking for Home ...

Recruitment Genius: Web Team Leader

£30000 - £35000 per annum: Recruitment Genius: One of the UK's leading web des...

Recruitment Genius: Client Manager

£27000 - £35000 per annum: Recruitment Genius: A growing, successful, friendly...

Day In a Page

Greece says 'No': A night of huge celebrations in Athens as voters decisively back Tsipras and his anti-austerity stance in historic referendum

Greece referendum

Greeks say 'No' to austerity and plunge Europe into crisis
Ten years after the 7/7 terror attacks, is Britain an altered state?

7/7 bombings anniversary

Ten years after the terror attacks, is Britain an altered state?
Beautiful evening dresses are some of the loveliest Donatella has created

Versace haute couture review

Beautiful evening dresses are some of the loveliest Donatella has ever created
No hope and no jobs, so Gaza's young risk their lives, climb the fence and run for it

No hope and no jobs in Gaza

So the young risk their lives and run for it
Fashion apps: Retailers roll together shopping and social networking for mobile customers

Fashion apps

Retailers roll together shopping and social networking for mobile customers
The Greek referendum exposes a gaping hole at the heart of the European Union – its distinct lack of any genuine popular legitimacy

Gaping hole at the heart of the European Union

Treatment of Greece has shown up a lack of genuine legitimacy
Number of young homeless in Britain 'more than three times the official figures'

'Everything changed when I went to the hostel'

Number of young homeless people in Britain is 'more than three times the official figures'
Compton Cricket Club

Compton Cricket Club

Portraits of LA cricketers from notorious suburb to be displayed in London
London now the global money-laundering centre for the drug trade, says crime expert

Wlecome to London, drug money-laundering centre for the world

'Mexico is its heart and London is its head'
The Buddhist temple minutes from Centre Court that helps a winner keep on winning

The Buddhist temple minutes from Centre Court

It helps a winner keep on winning
Is this the future of flying: battery-powered planes made of plastic, and without flight decks?

Is this the future of flying?

Battery-powered planes made of plastic, and without flight decks
Isis are barbarians – but the Caliphate is a dream at the heart of all Muslim traditions

Isis are barbarians

but the Caliphate is an ancient Muslim ideal
The Brink's-Mat curse strikes again: three tons of stolen gold that brought only grief

Curse of Brink's Mat strikes again

Death of John 'Goldfinger' Palmer the latest killing related to 1983 heist
Greece debt crisis: 'The ministers talk to us about miracles' – why Greeks are cynical ahead of the bailout referendum

'The ministers talk to us about miracles'

Why Greeks are cynical ahead of the bailout referendum
Call of the wild: How science is learning to decode the way animals communicate

Call of the wild

How science is learning to decode the way animals communicate