Studying his screen, he smiles briefly. "High pressure coming."

Andy Page has the English gift of understatement. The lead weather forecaster for the London Olympics, he's the man in charge of predicting conditions for key events from the 100 metres to the archery.

Page will coordinate a team of a dozen or so meteorologists at venues across the country as they grapple with England's notoriously fickle climate.

Even at the best of times, it would be a challenge. So far, its been one of the worst. After the wettest June in a century, a warm spell finally arrived and in the days running up to the opening ceremony, had mushroomed into a heatwave.

Records for weather extremes have been smashed around the northern hemisphere, in a trend that government scientists say is connected to climate change.

People from Pellston in Michigan to Krymsk in Russia have been confronted by heat, drought, flood, violent storms and hot rain.

Against this backdrop, athletes may find themselves competing against the British weather.

Sprinters like Usain Bolt need warmth to excel, tennis players and horses need ground that's not too soggy, and rowers and sailors need to be off the water if a storm hits.

As long as there's no risk of lightning, most events -- including the sprints -- will go ahead whatever the weather. There is leeway to reschedule some, and organisers say spectators may bring a small umbrella.

"It's just been non-stop," said Page, who in 23 years of forecasting has found the weather this summer to be exceptionally capricious. "If the weather pattern was to carry on, obviously the pressure would be even more."

DON'T MIND

People in England open conversations with the weather, which they have famously put up with since it helped them beat the French in battle in 1415.

It's a focus from childhood on. A.A. Milne's storybook character Pooh bear uses a balloon to pretend to be a raincloud, and a Beatles song, "Rain", was one of the first pop videos.

But knowing when or where the rain is going to fall has always been the hardest.

"We say it's going to be sunny spells but also scattered showers, and people think you're just trying to get out of giving them any detail," says Page, who works for the Met Office, the British government forecasting service that is providing location-specific weather advice for Olympic events.

"The problem is, the showers only have a life-cycle of about an hour to an hour and a half."

Forecasters work 12-hour shifts -- midnight to midday; midday to midnight -- and run computer simulations based on an array of data including details from radars which pick up the echoes from rain drops, as well as new high-definition information collected at a finer scale.

One system Page uses is called the "ensemble". It shows 50 different weather possibilities based on what's happening now. Each simulation runs 54 hours ahead, and models the possible impact of the slightest imaginable change.

When most of the charts -- forecasters call them 'postage stamps' -- agree, the forecasters are more confident about their predictions.

"We've got an awful lot of information, and the skill these days is being able to sift that information rapidly," says Page, whose career started out with observations plotted on sheets of paper for the Royal Air Force.

Experience helps. And timing is everything, especially for people out on water in potentially stormy conditions.

JET STREAM

In the Met Office canteen, fluffy model clouds hang from the high ceiling. Made with unbleached sheep's wool, they're a staff talking point, because some are dirty brown rather than fluffy white. But none are as dark as the clouds Britain has seen this summer.

"When it does rain, it is heavier," Met Office climate scientists said in a note this month about the reasons for this year's unpredictability.

That's logical, said forecaster Dave Britton. The global temperature has increased by 0.7 degrees Celsius since the industrial revolution, and the amount of moisture in the atmosphere has increased by four to five percent since the 1970s.

But the other force behind this year's freak weather is a phenomenon people have not needed to know about for years: the jet stream, a narrow band of fast-moving winds that runs from west to east across the Atlantic high up in the atmosphere.

In 2012 its been slower than usual, which has made its course more undulating.

Places like England are usually to the south of the jet stream in summer but this year, the stream has been nearer to the equator. That has trapped the country under Arctic air.

Many other places have also been affected: parts of the United States have been locked to the south of the stream, resulting in record heat and drought.

On a July 19 visit, Page's models were suggesting the jet stream would return to its typical path, at least for a few days. Whether it stays will be significant for weather patterns, and he was not guessing.

"It's changing all the time."

It's also not yet clear why the stream has been slow, although possible reasons include global warming, which reduces the temperature contrast between the frozen poles and the hot equator. A large chunk of glacier broke off in the Arctic recently.

SEED THE CLOUD?

Never mind predicting it, can't British scientists just change the weather, like the Chinese did for some of the time at Beijing in 2008?

China says its cloud-seeding techniques made sure rain fell far away from the Games at crucial moments.

Its state planning agency, the National Development and Reform Administration, has earmarked around 340 million yuan for weather modification, which usually involves firing chemicals into clouds to encourage raindrops to form where you want rain.

The China Meteorological Administration did not respond to requests for comment on the London Games.

At the British Met Office, forecasters are sceptical about the science. They say there is not enough evidence that weather modification works to justify the expense.

But there's also something very English about their response.

"That's not what the weather's about," said forecaster Charles Powell. "It's like trying to change the course of a river. The weather is going to do what it's going to do, regardless." (With additional reporting by David Stanway in Beijing; Editing by Greg Stutchbury)

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