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?
SPONSORED FEATURES
Independent Dating
and  

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

iJobs Job Widget
iJobs General

Recruitment Genius: Class 2 Drivers

£31700 per annum: Recruitment Genius: This specialist wholesaler owned and man...

Recruitment Genius: Laser and Router Operative

£18000 - £22000 per annum: Recruitment Genius: A Laser and Router Operative is...

Recruitment Genius: IT Support Technician - 1st Line

£15000 - £20000 per annum: Recruitment Genius: They have been providing local ...

Recruitment Genius: Field Sales Executive / Trainee Managers

£6000 - £50000 per annum: Recruitment Genius: They are looking for smart, orga...

Day In a Page

Refugee crisis: David Cameron lowered the flag for the dead king of Saudi Arabia - will he do the same honour for little Aylan Kurdi?

Cameron lowered the flag for the dead king of Saudi Arabia...

But will he do the same honour for little Aylan Kurdi, asks Robert Fisk
Our leaders lack courage in this refugee crisis. We are shamed by our European neighbours

Our leaders lack courage in this refugee crisis. We are shamed by our European neighbours

Humanity must be at the heart of politics, says Jeremy Corbyn
Joe Biden's 'tease tour': Could the US Vice-President be testing the water for a presidential run?

Joe Biden's 'tease tour'

Could the US Vice-President be testing the water for a presidential run?
Britain's 24-hour culture: With the 'leisured society' a distant dream we're working longer and less regular hours than ever

Britain's 24-hour culture

With the 'leisured society' a distant dream we're working longer and less regular hours than ever
Diplomacy board game: Treachery is the way to win - which makes it just like the real thing

The addictive nature of Diplomacy

Bullying, betrayal, aggression – it may be just a board game, but the family that plays Diplomacy may never look at each other in the same way again
Lady Chatterley's Lover: Racy underwear for fans of DH Lawrence's equally racy tome

Fashion: Ooh, Lady Chatterley!

Take inspiration from DH Lawrence's racy tome with equally racy underwear
8 best children's clocks

Tick-tock: 8 best children's clocks

Whether you’re teaching them to tell the time or putting the finishing touches to a nursery, there’s a ticker for that
Charlie Austin: Queens Park Rangers striker says ‘If the move is not right, I’m not going’

Charlie Austin: ‘If the move is not right, I’m not going’

After hitting 18 goals in the Premier League last season, the QPR striker was the great non-deal of transfer deadline day. But he says he'd preferred another shot at promotion
Isis profits from destruction of antiquities by selling relics to dealers - and then blowing up the buildings they come from to conceal the evidence of looting

How Isis profits from destruction of antiquities

Robert Fisk on the terrorist group's manipulation of the market to increase the price of artefacts
Labour leadership: Andy Burnham urges Jeremy Corbyn voters to think again in last-minute plea

'If we lose touch we’ll end up with two decades of the Tories'

In an exclusive interview, Andy Burnham urges Jeremy Corbyn voters to think again in last-minute plea
Tunisia fears its Arab Spring could be reversed as the new regime becomes as intolerant of dissent as its predecessor

The Arab Spring reversed

Tunisian protesters fear that a new law will whitewash corrupt businessmen and officials, but they are finding that the new regime is becoming as intolerant of dissent as its predecessor
King Arthur: Legendary figure was real and lived most of his life in Strathclyde, academic claims

Academic claims King Arthur was real - and reveals where he lived

Dr Andrew Breeze says the legendary figure did exist – but was a general, not a king
Who is Oliver Bonas and how has he captured middle-class hearts?

Who is Oliver Bonas?

It's the first high-street store to pay its staff the living wage, and it saw out the recession in style
Earth has 'lost more than half its trees' since humans first started cutting them down

Axe-wielding Man fells half the world’s trees – leaving us just 422 each

However, the number of trees may be eight times higher than previously thought
60 years of Scalextric: Model cars are now stuffed with as much tech as real ones

60 years of Scalextric

Model cars are now stuffed with as much tech as real ones