The Brown Willy effect is a particular example of a meteorological phenomenon known as peninsular convergence, which sometimes occurs in the south-west of Great Britain. It leads to heavy showers developing over the high ground of Bodmin Moor in Cornwall, which then often travel a considerable distance downwind of their place of origin. The effect is named after the hill, Brown Willy, the highest point on the moor and in Cornwall as a whole. It is thought that the Boscastle flood of 2004 was caused by a particularly extreme example.