Atmospheric Rivers and Enhanced Integrated Vapor Transport Probability Forecasts as seen during Frontal Passages in Southern California with an Emphasis on Strong Wind Episodes

Atmospheric Rivers are frequent visitors to the west coast, but only on occasion do they slide far enough south to significantly affect Southern California. With the stronger events, heavy rain or snow occurs, and at times severe weather. Integrated water vapor transport (IVT) is a good parameter for determining moisture advection into the region, and is enhanced during frontal events. This IVT consists of imbedded strong flow combined with significant amounts of moisture. Along with instability, this can result in the generation of damaging frontal passages, both from a convective standpoint and a synoptic scale wind standpoint. Enhanced IVT moving into the region can impact arrival rates at major airports due to nearby thunderstorms and associated precipitation, or when strong winds develop. Tree damage can be rather common, and may result in power outages. The main purpose of this study is to make some brief comparisons of IVT from the perspective of probability forecasts to damaging impacts in the region using the National Center for Environmental Prediction (NCEP) GFS Ensemble Prediction System. The focus will be on the more damaging frontal passages during the recent cool season (2015-2016), including an event that was considered to be rather "extreme" for Southern California.