Forecasting an extreme precipitation event in Norway

In August 2003 heavy precipitation occurred in the northern part of South-Norway. The event is simulated from initial conditions at different times to gain insight into the predictability of the high-impact weather event. A forty-eight hours forecast fails to predict the intensity of the precipitation, while the event is reproduced reasonably well in a 24 hours forecast. The improvement between the forecasts is mainly associated with an increase in intensity and improved direction of low-level winds that impinge the mountains. The errors in the winds in the 48 hours forecast were associated with a local underestimation of temperatures in the lower part of the troposphere in the analysis. This study is a part of the THORPEX programme on the predictability of high-impact weather