Rain clouds usually leave as quickly as they arrive. But not this time...

The weather
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The Independent Online

Weather experts talk about a moving "conveyor belt" of rain when describing Britain's continuous exposure to weather systems as they roll in from the North Atlantic. But the conveyor belt of rain over north-west England and southern Scotland over the past three days got stuck over the hills of Cumbria and southern Scotland.

The long weather system extended south-west from Britain for thousands of miles into the Atlantic. Normally, the rain clouds would have made rapid progress on stiff, south-westerly winds but, for a critical 36-hour period, they fed into a stationary low-pressure area, resulting in record rainfall over the North-west. The clouds that formed within the weather system over the Atlantic this week were pushed north-west towards Britain by prevailing winds. When these warm, moist air-masses were blown over the hills of northern England they cooled, allowing the moisture they contained to condense as heavy rain.

This part of Britain had experienced heavy rain during the previous week so the ground was already severely waterlogged. Because rain fell continuously for 36 hours on saturated ground, the water quickly ran off to swell rivers, resulting in the devastating floods in towns such as Workington and Cockermouth.

The Environment Agency said the rainfall over Cumbria reached record levels, its rain gauge at Seathwaite Farm recording 314.4mm (12.4ins) in 24 hours up to 00.45am on Friday. The previous record was at Martinstown in Dorset in July 1955, which recorded 279mm (11ins) in 24 hours, said a Met Office spokesman. Over 36 hours between Wednesday evening and Friday morning Seathwaite recorded 372mm (14.6ins) of rain. This is the sort of rainfall record likely to be broken only once in every 125 years, the spokesman said.

"We are forecasting further rain and strong winds on Saturday," he added. "This rain could slow recovery on the river network in Cumbria and south-west Scotland but should not exacerbate the overall situation in Cumbria and the borders of Scotland. "The outlook is for more unsettled weather, but not on the scale of the rainfall seen this week. More heavy rain will fall on Saturday, particularly in the western part of the UK.

"This will spread north through Wales and arrive in Cumbria about lunchtime and will persist for several hours. This rain will be followed by showers, which are expected again on Sunday, giving way to more persistent rain later on Monday. There will be a further band of rain moving in from the west late on Tuesday. This rainfall will maintain the high river level, but is not expected to exacerbate the situation."

The Atlantic, which is relatively warm at this time of the year compared to ground temperatures, triggers the formation of deep low-pressure systems which can extend over many thousands of square miles. They possess more stored energy than a hurricane, albeit dispersed over a wider area. Warmer air can hold more moisture than cold air which is why Britain tends to get heavier downpours in summer and autumn than winter and spring. Warmer sea temperatures are forecast with global warming but the recent flooding cannot be linked directly to climate change, the spokesman said.

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