Brown Willy effect
The Brown Willy effect is a weather pattern seen in the south-west of Great Britain. It makes heavy showers form over Bodmin Moor in Cornwall, and these showers often travel a long way downwind. It’s named after Brown Willy, the highest hill on the moor and in Cornwall.
It happens when mild, moist winds blow from the Atlantic toward Cornwall. As they hit land, friction slows them and can bend them a bit toward the north. This creates a spot where the winds meet and air is pushed up, helping rain to form. Bodmin Moor’s height makes the lifting stronger.
In summer, the land heats up more than the sea, so sea breezes come in from both coasts. When these sea breeze fronts meet, air rises quickly over the moor and heavy showers or thunderstorms can develop.
The showers then move with the prevailing wind, usually east or northeast, creating a thin line of rain along the length of the south-west peninsula. The line often grows stronger as it passes Dartmoor and the Blackdown Hills.
People in the path get several heavy downpours, while nearby places stay dry. Notable examples include 23 August 2004, and 27 March 2006, when a continuous line of showers stretched from Bodmin Moor to Burford, Oxfordshire, about 145 miles (233 km) away.
This page was last edited on 2 February 2026, at 17:42 (CET).