As the southwesterly flow crossed Cornwall, surface frictional effects caused the flow to decrease and back over the land, and a convergence line developed between the moderate southwesterlies over the sea and the light south-southwesterlies over Cornwall itself. This convergence line lay roughly parallel to the north Cornish coast from St Ives to Newquay, but it crossed the coast between Newquay and Boscastle. The uplift feeding the convective process was therefore accelerated over the western flank of Bodmin Moor (known hereabouts as Davidstow Moor) resulting in a prolonged in-situ generation of active cumulonimbus clouds. This is why the downpour lasted for four hours.