Clustering methods for statistical downscaling in short-range weather forecast

In this paper we present an application of clustering algorithms for statistical downscaling in short-range weather forecast. The advantages of this technique compared with standard nearest neighbors analog methods are described both in terms of computational efficiency and forecast skill. We report some validation results of daily precipitation and maximum wind speed operative downscaling (lead time 1 to 5 days) on a network of 100 stations in the Iberian Peninsula the period 1998-1999. These results indicate that the weighting clustering method introduced in this paper clearly outperforms standard analog techniques for nfrequent, or extreme, events (precipitation > 20mm, wind > 80km/h). Outputs of an operative circulation model on different local-area or large-scale grids are considered to characterize the atmospheric circulation patterns, and the skill of both alternatives is compared.The authors are also grateful to the University of Cantabria, CSIC, and the Comisión Interministerial de Ciencia y Tecnología (CICYT; Grant REN2000-1572) for partial support of this work