The hill is known for a meteorological phenomenon known as the Brown Willy effect , in which heavy rainfall develops over high ground and then travels downwind for a long distance . The effect produces heavy localised rain which can cause disastrous flash flooding such as the Boscastle flood of 2004 . In another case when the effect was manifested , a continuous line of showers developed on 27 March 2006 stretching 145 miles from Brown Willy to Oxfordshire
Boscastle flood of 2004
Boscastle flood of 2004
Brown Willy