Wind Profiler and Surface Observations of Easterly Gap Flow and Precipitation in the Columbia River Gorge

An observational study of westward-directed gap flows through the Columbia River Gorge (CRG) during two winter seasons between October 2015 and April 2017 is presented. The study uses data collected by three Doppler wind profilers and several surface meteorology stations and focuses on the gap exit region near Troutdale, Oregon. The CRG is the largest and lowest cross-barrier passage in the Cascade Mountains of Oregon and Washington, and it is the most prominent location in the region where coastal and continental air masses are channeled through the mountainous terrain as gap flows. The CRG is generally <10 km wide below ~700 m MSL and increases in width to ~80 km in the layer between 700 and 2000 m MSL. During the cool season, low pressure dominates offshore and high pressure dominates inland, resulting in the westward extrusion (i.e., easterly gap flow) of cold continental air through the gorge into the normally maritime environment of the Portland, Oregon, metropolitan area (PMA). Cool-season easterly gap-flow conditions can produce damaging winds in the western gorge and around the PMA. Also, reliable winds funneling through the gorge (both westbound and eastbound) make this region ideal for wind energy production. Easterly gap-flow conditions can also result in snow and freezing rain, as the shallow easterlies undercut moist onshore flow associated with landfalling extratropical cyclones from the Pacific. We will present results based on the 92 easterly gap flow events that occurred during the two cool seasons, as well as case study examples that involved hazardous and damaging weather in the PMA.