A wind turbine has a Lidar device to sense wind conditions upstream of the wind turbine including wind speed, direction and turbulence. Signals from the Lidar are processed to detect an event which could give rise to low cycle fatigue loading on one or more components of the wind turbine. On detection the system controller takes the necessary evasive action depending on the nature and severity of the extreme condition detected. This may include a significant reduction in power generated through reduction in rotor speed or torque, complete shutdown of the generator and yawing of the nacelle and rotor in response to a change in wind direction.