Large-scale dynamics of extreme precipitation events in California during winter 2016-2017

Benjamin Moore

Tuesday, Mar 06, 2018, 2:00 pm
DSRC Room 2A305


Abstract

This study examines large-scale dynamical processes contributing to the occurrence of extreme precipitation events in California during winter 2016-2017. In particular, the two largest events (8-11 January 2017 and 6-11 February 2017), which collectively accounted for ~38% of the total seasonal precipitation volume over northern California, are investigated. Notably, these two events occurred within similar large-scale flow patterns over the North Pacific, featuring a major high-latitude blocking ridge over the central North Pacific and an active subtropical storm track across the North Pacific. The formation and persistence of these flow patterns are found to have involved influences of tropical convection and complex interactions between Rossby wave trains along the polar and subtropical jet streams over Asia and the North Pacific. In both events, a corridor of strong water vapor flux impinging upon the California coast was established and maintained in the warm sector of a slow-moving cyclone over the eastern North Pacific that developed in conjunction with a phasing and interaction of a polar and a subtropical disturbance on the eastern flank of the blocking ridge. A brief climatological analysis is conducted to place the two precipitation events under investigation into context and to investigate the degree to which the large-scale flow pattern associated with the events represents a principal dynamical pathway for the occurrence of extreme precipitation in California.



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