Analysis of large forecast errors over Iceland

In a dataset of 5 years, forty worst cases of failures of a numerical forecast to accurately reproduce the low level wind speed over Keflavík, SW-Iceland are studied. An overestimation of the wind by the model occurs in most cases when the forecasted low-level winds are from the southeast and winds at higher levels are from the southwest, while northeasterly winds are overrepresented in the group of large underestimations of the winds by the model. The overestimated southeasterly winds are associated with fronts that have a limited horizontal extension and move fast in some cases. The underestimation of the northeasterly winds appears on the other hand to be associated with non-resolved orography and a corner effect. There is no obvious systematic clustering in the tracks of the poorly predicted weather systems.