Since the mountain range has a high number of valleys, the Segre river valley (Catalonia, Spain) was the first one chosen to carry out the study. Its classification derived through several techniques is presented here. Firstly, field observations from AWS have been used for statistical analysis based on regression, cluster and Empirical Orthogonal Functions (EOF). Secondly, the effects of nocturnal down-valley flows have been studied in more detail using a drainage wind model (KLAM_21 operated by the Deutscher Wetterdienst) as well as evaluations of the Topographical Amplification Factor (TAF).
Finally, from the combination of all techniques (Lundquist and Pepin) an idea about the cold air behavior has been elaborated in relation to the CAP events within the Segre river valley.