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Page last updated at 09:42 GMT, Thursday, 10 July 2008 10:42 UK

Was Wednesday's washout a monsoon?

Bath shoppers on 9 July 2008

The Magazine answers...

While much of Europe is experiencing a heatwave, the UK has been fighting flash floods and can expect a soggy weekend. The papers are calling it a monsoon - is it?

You could be forgiven for thinking the answer is yes. Yesterday the Daily Mirror reported that we would receive "one month's rain in a day," the Daily Telegraph mentioned a "European monsoon" and the Daily Mail proclaimed: "And now the monsoon!"

And after last summer's dismal downpours, the 2006 of warm summer evenings and hosepipe bans seems a distant memory.

But according to meteorologists, Wednesday's washout was not a monsoon - day or season.

"A monsoon only affects one part of the world and that is the Indian subcontinent," says Jim Dale, senior meteorologist at British Weather Services.

The term is commonly misused to describe heavy rain - when it actually refers to the wind, specifically the seasonal reversal of wind direction. However, it's more loosely used by hydrologists, to refer to rainfall in any part of the world where the majority of rain falls in a particular season.

Britain is not in a monsoon
Monsoon is a wind - not rain
India's monsoon starts on 1 June

Ceratinly, the predictable periods of rainfall that a monsoon brings are very different to the UK's recent lashings.

"The monsoon takes a long time to onset," says BBC broadcast meteorologist Susan Powell, talking specifically of the Indian weather pattern. "It is seasonal and has a set start date of 1 June. It is a formulaic process,"

She says the downpours cannot really describe what we have been experiencing as monsoon-style weather because the origin is so different.

But the heavy rains are definitely exceptional.

"We had about 60mm (2.4 inches) on Wednesday, which is unseasonable for July," she says.

The UK usually receives that amount in the whole of July.

Persistent rain

According to the Met, between 1971 and 2000 the average UK rainfall for the whole of July was 69.6mm (2.7 inches).

A day like yesterday happens, on average, a couple of times a year during the summer - but is much more typical of early spring or late autumn.

A regular feature in the BBC News Magazine - aiming to answer some of the questions behind the headlines

But although rain in July is not an unusual event, Ms Powell says it normally occurs when heat builds up, resulting in thunder storms.

Instead, these rains are being brought by winds rolling off the Atlantic.

"It is nothing to do with global warming, Gordon Brown or the price of oil," says Mr Dale.

He thinks it is not just the rain's intensity, but also its persistence which is surprising. Normally downpours last a few hours - yesterday it lasted from dawn to dusk and beyond.

"Wednesday will be a marker day," says Mr Dale. "Rising rivers will break their banks, there will be flash floods, a rise in road accidents and more insurance claims."

Hardly anywhere escaped the deluge.

The south-west, south, and south-east parts of England, and south Wales, northern Ireland and parts of northern England and southern Scotland were all warned of a moderate risk for a "severe weather event" by the Met.

And by the afternoon The Environment Agency had issued six flood warnings in the south-west and Wales, while 27 "flood watch" areas were being ministered, including nine in the Thames Valley.

Heavy rainfall is expected to move northwards on Thursday, and the BBC is predicting more heavy weather at the weekend.

But Mr Dale says the dark clouds will have a silver lining.

"I am very optimistic that by the time school's out the UK will see a massive improvement."



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