Case Study of a Land Falling Atmospheric River in Northern California: In Situ Dropsonde Observations Compared to WRF Model Outputs and NCEP Final Analysis

Abstract:

Atmospheric rivers (AR) play a crucial role in moderating California's water budget with statewide precipitation totals depending almost entirely on the arrival of a small number of storms. In this study we aim to analyze the in situ measurements taken by dropsondes in and around a February 2014 AR over the course of several days, which produced heavy precipitation in Northern California. We find, as in other AR case studies, that the high magnitude winds in the form of low level jets (LLJs) with unusually high water vapor content and stable air masses interact with coastal mountains to produce heavy precipitation near the coast. This study compares the dropsonde observations with NCEP Final Analysis data and Weather Research and Forecasting (WRF) model outputs. In particular, we compare the forecasts of integrated vapor transport (IVT) against that which was measured by the dropsondes. Model forecasts and observation data of IVT will be presented at the AGU Fall Meeting.