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

• DOI: 10.1175/jhm-d-14-0139.1
• Publication Date: 2015-01-28T17:44:54Z
• Authors: Michael A. Alexander; James D. Scott; Dustin Swales; Mimi R. Abel; Kelly Mahoney; Catherine A. Smith
• Keywords: Trough (economics)

Abstract Two methods were used to identify the paths of moisture transport that reach U.S. Intermountain West (IMW) during heavy precipitation events in winter. In first, top 150 at stations located within six regions IMW identified, and then back trajectories initiated 6-h intervals on those days four Climate Forecast System Reanalysis grid points nearest stations. The second method identified leading patterns integrated water vapor (IVT) using three empirical orthogonal functions IVT over land first normalized by local standard deviation. 1% associated 6-hourly time series was construct composites IVT, atmospheric circulation, precipitation. results from both indicate originating Pacific leads extreme winter takes distinct pathways is influenced gaps Cascades (Oregon–Washington), Sierra Nevada (California), Peninsular Ranges (from Southern California through Baja California). transported along these routes appears be primary source for mountain ranges IMW. synoptic conditions with dominant include a trough–ridge couplet 500 hPa, trough northwest ridge where circulation funnels west-southwest into