Estimation of bora wind gusts using a limited area model

A performance of the wind gust estimate (WGE) method on the bora wind has been examined. Numerical simulations of several bora episodes have been performed using a non-hydrostatic mesoscale model MEMO6. The model captured well the onset and cessation of the bora while the agreement between simulated and observed wind speeds differed from episode to episode. In cases with accurately simulated wind speeds, the WGE results were very good, thus indicating that the method could be used in forecasting bora gusts.

The performance of the WGE method for the examined bora cases also suggested a possibility of further simplification of the method for the bora applications. Inspection of the bora flow and its thermodynamical structure revealed that after the bora onset the shear instabilities completely overwhelm the buoyant forces. This means that the parcels with the maximum wind speed in the boundary layer will always be able to reach the surface and result in wind gusts. Therefore, it is enough to have only a vertical profile of the wind speed. Although completely derived from the physical considerations, this represents a very simple way of determining bora wind gusts and can thus be easily implemented in the operational bora wind forecasting models.