Large-scale flow patterns associated with long-duration extreme precipitation events in northern California

Ben Moore


Thursday, Aug 29, 2019, 11:00 am
DSRC Room GC402


In this study, large-scale flow patterns that promote long-duration (i.e., 7-day) extreme precipitation events in northern California are investigated. A climatology of extreme precipitation events is constructed for 1979–2017, and the events are categorized by applying an objective clustering method to upper-level geopotential height anomaly fields corresponding to the events. Four categories of extreme precipitation events are identified, corresponding respectively to four distinct large-scale flow patterns. Dynamical processes supporting extreme precipitation in northern California are investigated for each category through composite analysis and brief case studies. A climatology of flow patterns closely resembling those for the four precipitation event categories is then constructed based on a simple analog index, and a statistical analysis is performed to quantify the relationship between the occurrence of the patterns and the occurrence of extreme precipitation in northern California. Finally, the skill of medium-range and subseasonal ECMWF reforecasts in predicting the occurrence of the flow patterns and associated precipitation along the U.S. West Coast is assessed.


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