Self-organizing maps (SOMs) were used to explore relationships between large-scale synoptic conditions, especially vertically integrated water vapor transport (IVT), and extreme precipitation events in the U.S. Intermountain West (IMW). By examining spatial patterns in the IVT, pathways are identified where moisture can penetrate into the IMW. A substantial number of extreme precipitation events in the IMW are associated with infrequently occurring synoptic patterns. The transition frequency between each of the SOM nodes, which indicate temporal relationships between the patterns, identified two synoptic settings associated with extreme precipitation in the IMW: (1) a landfalling, zonally propagating trough that results in a concentrated IVT band that moves southward as the system moves inland and (2) a southwesterly storm track associated with strong ridging over the coast that results in persistent IVT transport into the Pacific Northwest that can last for several days.

Office of Oceanic and Atmospheric Research (OAR)