A DEADLY combination of coastal winds, unstable air and heavy rain led to flash floods that ripped through Boscastle.

Wayne Elliot, Met Office forecaster, said: ''This weather pattern formed locally. The air was unstable, which allowed for bad weather, and then there was a trigger mechanism in one location.''

This unstable air was created by two air masses, one inland and one offshore. When they converged, it triggered the air to rise, cooling and creating rain.

In addition, coastal winds were converging on the area, giving extra strength to the weather, Mr Elliott said.

''We can't forecast exactly where these conditions are going to be but we do know the area is at risk. There have been a lot of big flooding events in the south west in which unbelievable amounts of rain can fall.''

The location of Boscastle makes it particularly vulnerable. In this case, the village stands in a deep coomb where two valleys meet, formed by the rivers Valency and Jordan. A third river, Paradise, also flows through the village.

Inland, the high ground of the moorland acts as a trigger for the weather. Much of the rain fell on the high areas and flowed downriver to flood the valleys.

The pattern of weather is similar to that which caused the 1952 flood at Lynmouth in which 34 people were killed. In that incident, 18 hours of rain caused by an Atlantic depression combined with unstable air rising over Exmoor which increased the rainfall.

The water flooded down the East and West Lyn rivers which join at Lynmouth and swamped the town, destroying homes and washing away vehicles.