Influence of Columbia Gorge Gap Winds on the Occurrence of Freezing Rain at Portland International Airport

The Columbia River Gorge is the largest gap in the Cascade mountain range. It is also the only gap with a near sea level base. The gorge is connected to the Columbia Basin which is located to the east of the Cascades in Washington state. Twice a year on average during the winter season, persistent cold air pool events cause low laying cold air to remain in the Columbia Basin. This pooling occurs when a surface high pressure moves south from Canada into the Pacific Northwest and forces continental polar air to flow south into the Columbia Basin. Due to this high pressure on the east side of the Cascades, the cold air that has pooled into the Columbia Basin is channeled into the Columbia Gorge. The cold air is then advected west through the gorge by the gap winds.

Portland International Airport (PDX) is located west of the exit of the Columbia Gorge.  The gap winds that occur during a cold pooling event advect cold temperature into the PDX area, which helps induce an inversion. When precipitation occurs during an inversion event, freezing rain may occur. To study influence of the gap winds on freezing rain and the occurrence of freezing rain during a gap wind event, data was obtained from the National Oceanic and Atmospheric Association's Cooperative Observers Network. The data includes precipitation, wind direction, wind speed and weather type from six different locations along the Columbia Gorge starting January 1st 1960, through December 31st 2015. Using data, correlations of gap winds and freezing rain can be made, along with the study of parameters during the formation of synoptic weather patterns that cause gap winds.