A Case Study of Four Atmospheric River Events Over the Pacific West Coast

Atmospheric Rivers (ARs) are moisture phenomena related to cyclones which bring moisture and large amounts of precipitation to areas of enhanced elevation along coastal areas. These events bring much of the rain received by the state of California, and the past winter was no exception, as many AR events brought much-needed rain to the region. Four different events from the 2016 fall through 2017 spring seasons are examined to better identify the relative roles of long-range moisture transport versus local moisture fluxes in AR events. Cross-sections of areas and times of interest during each event are generated, along with trajectory analyses of each event which will aid in determining the origin of the moisture being moved over land. Both the cross-sections and the trajectory analysis are taken from the CFSR (Climate Forecast System Reanalysis) model. It is expected that the results of these processes will support the findings of Dacre et al. (2015), which show that the moisture anomaly present during AR events is not actually due to moisture transport directly along the AR itself. Rather, the AR is the result of moisture convergence due to a combination of the warm conveyor belt forcing the ascent of moisture over the warm front and the trailing cold front forcing ascent as it closes the gap between itself and the warm front. The importance of this research is first and foremost evident in the California region, as water conservation in California, a naturally dry area, is extremely important to the ever-expanding cities and communities present there and require long-term planning. Such planning is made much more effective when we better understand the forces that bring much of the precipitation to the area.