Uncertainties in forecasting orographic flows

The accuracy of a large set of high-resolution wind speed forecasts with different lead times is assessed for different parts of orographic flows, including upstream blockings, gap winds, corner winds, wakes and downslope winds.  The by far largest errors are in areas of downslope windstorms, but there are also considerable errors in the other parts of orographic disturbances to the flow and they are greater than in non-orographic flows in the same region.  The errors are discussed in view of the different dynamics and kinematics of the flows.  They are partly related to intermittency of i.e. gravity waves as well as strong spatial gradients in the wind field.