Orographic Precipitation Over the Olympic Mountains – A Comparison of Rain Patterns at Two Weather Stations

During the Fall of 2015 through the Winter of 2016, the Olympic Mountains Experiment (OLYMPEX) took place over the Olympic Mountain Range in Washington State. The goals of OLYMPEX are to provide ground validation for the Global Precipitation Measurement (GPM) core satellite, and to determine the orographic effects on precipitation processes. OLYMPEX hosted a wide variety of ground instrumentation (rain gauges and disdrometers measuring particle size distribution), multiple radars and aircraft. Preliminary results from data collected during OLYMPEX have shown a variety of orographic precipitation enhancement patterns. In order to explore whether these patterns occurred during years other than the OLYMPEX field campaign, this research focuses on two stations that have been collecting precipitation data for a 9 year period. These stations are geographically located close together along the Quinault River valley, but differ slightly in elevation and with distance from the coast. The U.S. Climate Reference Network (CRN) site is located immediately northeast of Lake Quinault at a slightly lower elevation than the second station in Bunch Field, which is located closer to the higher terrain of the Olympic Range. Climatologically Bunch Field receives a noticeably larger amount of precipitation, however there are particular events when the CRN site receives more precipitation. In this study, the patterns of orographic enhancement of precipitation as seen through the precipitation measured at these two sites will be documented and related to synoptic conditions. The focus will be on documenting the meteorological parameters such as stability, low level jet intensity and moisture transport, when the CRN site receives more precipitation than Bunch Field. Early results from the OLYMPEX project have shown that the CRN sites can receive more precipitation during warm, wet events such as atmospheric river type storms. This study will document whether this was true during other winter seasons.