Evolution of Sierra Barrier Jets that occur simultaneously with atmospheric river events in a high resolution dynamical downscaling of the North American Regional Reanalysis

The Sierra Barrier Jet (SBJ) is a dynamically-generated low-level jet along the Sierra Nevada of California that influences precipitation distribution and aerosol/water vapor transport in the CA central valley. In an assessment of the climatological characteristics of the SBJ, Neiman et al (2010) found that over 85% of strong and long SBJs occurred simultaneously with atmospheric rivers (ARs) incident on the west coast. The occurrence of SBJs during landfalling ARs is of interest because of the SBJ’s potential to redistribute precipitation. This study documents the impact the SBJ has on precipitation distribution during landfalling AR events in a high resolution (6 km horizontal grid-spacing) downscaling of the North American Regional Reanalysis generated with the Weather Research and Forecast model for the time period October-April 2003-2010. The model’s ability to reproduce the observed SBJ - albeit with a slight weak bias - will be illustrated, as will its ability to capture the climatological distribution of precipitation. The evolution of atmospheric conditions during a composite of cases with AR conditions and strong or long SBJs will be presented to reveal the west-east spatial extent of the SBJ with respect to the Sierra Nevada, SBJ southward penetration, fate of the cold air present in the central valley prior to SBJ onset, and impact of the SBJ on precipitation distribution.