LAUSR

AbstractUsing a composite analysis for strong sea level pressure perturbations off the west coast of North America, the evolution of large-amplitude synoptic systems upstream of the Rocky Mountains is investigated for the winter season. Corresponding previous analyses are refined by avoiding multiple counting of events and extended by including potential vorticity, vertical motion, and deformation in the analysis.Cyclonic and anticyclonic anomalies behave similarly, with weak local extrema forming in the lee of the mountain range southeast of the parent systems. However, neither the geopotential anomaly nor the associated potential vorticity anomaly cross the mountain range. Nevertheless, these anomalies contribute to the sea level pressure anomaly in the lee. For both positive and negative anomalies, potential vorticity exhibits a bipolar structure with lobes over the reference point and over the Cordillera, respectively. The relevance of several theories describing the interaction between synoptic syste...