High-Resolution Atmospheric Simulations over Iceland for weather forecasting (HRAS)

High-Resolution Atmospheric Simulations over Iceland for weather forecasting (HRAS)

Since 30 March 2004, MM5 has been run for forecasting purposes 4 times a day for Iceland and the surrounding waters.

The simulations are forced with boundary conditions from the ECMWF BC project and the horizontal resolution started with 9, and became later 3 km. The simulations produce a mesoscale pattern of wind, temperature and precipitation that is often very different from more coarse-resolution simulations and is of great value for forecasting of local weather.

A weather forecasting diagramme for mountain flows will be presented and the patterns in the real-time simulations are discussed in the context of this diagramme. Here, the simulations reproduce very well features such as corner winds and the presence and absence of downslope windstorms.

For validation purposes, 15 years with a similar setup as the daily forecasts have been simulated and compared to observations. The comparison reveals that the variability and the magnitude of the mean winds is quite well reproduced, but there is a systematic underestimation of the wind speed in the central highlands of Iceland. The simulations also underestimate precipitation downstream of mountain ranges. Possible causes for such errors will be discussed.