Frontal Precipitation Enhancement Upstream of the Olympic Mountains during OLYMPEX IOP1

Analysis of data from the National Weather Service Langley Hill WSR-88D, in conjunction with soundings collected during the 2015 Olympic Mountain Experiment (OLYMPEX), examines the orographic enhancement upstream of the Olympic Mountains of Washington State. Throughout the world’s mountainous terrain, orographic precipitation enhancement greatly affects the total rainfall in these regions, and previous studies found that orographic enhancement plays a significant role in flooding and landslide events upstream of the mountains themselves. Dual-polarization radar scans and soundings from 29 October 2015 - 18 November 2015 observed several frontal and atmospheric river (AR) events. Hovmöller diagrams of radar reflectivity east and west of the radar indicate differences in the east-west propagation speeds of precipitation over time. By analyzing the propagation speeds and reflectivity values, this visualization technique also allows for the identification of different types of precipitation features. The east-west diagram provides a mostly sea-level view of precipitation, but beam blockage lessens the view to the east by the Cascade Mountains. These diagrams will record how the precipitation enhancement changes through different times of the day and with multiple different types of precipitation features such as narrow cold frontal rainbands (NCFRs). Future work will consist of the analysis of Hovmöller diagrams directed at where the predominant winds impinge on the mountains. This study will compare these viewing angles impinging on the Olympic Mountains to the east-west view to differentiate how the orographic enhancement changes with distance from the mountains.