Synoptic Climatology of 500-mb Winter Flow Types

Abstract

An objective correlation method is used to obtain seven typical 500-mb winter flow Patterns Over the western United States and eastern Pacific Ocean. The frequency of occurrence of each type is presented. The atmospheric configurations of each type are described in terms of 850-, 500- and 300-mb heights, 850-mb dewpoint depressions, 500-nib absolute Yorticities and vertical velocities, relative frequency of precipitation, and other related fields. The distinctness of the types over different geographical locations is discussed. The relative frequency of precipitation at 42 western stations is well differentiated by the seven types. This suggests that the stratified relative frequencies could he used as a first refinement over simple climatology when other more accurate quantitative precipitation forecasts are not available.