Moisture Pathways into the U.S. Intermountain West Associated with Heavy Winter Precipitation Events

The semiarid U.S. Intermountain West (IMW) can experience extreme precipitation events during the cool season (Oct-Mar). The moisture source(s) for these extreme events are explored using two independent methods. In the first, the top 150 precipitation events at stations located within six regions in the IMW were identified and back-trajectories were initiated at the four nearest Climate Forecast System Reanalysis (CFSR) grid points every 6 hours. The second method identified the leading patterns of integrated vapor transport (IVT) using the three leading EOFs of IVT over land. For both methods it is shown that moisture originates from over the Pacific and follows distinct pathways through the complex terrain of the IMW. These pathways are influenced in gaps in the Cascades (Oregon-Washington), the Sierra Nevada (California) and the Peninsular ranges (Southern California extending south into the Baja Peninsula).