Assessment of numerical weather forecasts over SW-Iceland

Five years of 48 hours numerical forecasts of wind and temperature at different levels in the lower troposphere are compared to radiosonde observations at Keflavík, SW-Iceland. The overall accuracy of the forecasts is very good at all levels. At the lowest levels, there is however a slight cold bias in the forecasted temperatures during westerly winds. There is also a cyclonic bias in the forecasted wind direction in northerly flow. Both these biases can be attributed to the impact of non-resolved orography: The cold bias appears to be associated with an underestimation of an upstream blocking, and the wind bias to an underestimation of the wake south of Iceland.