A Climatological History of Tornadoes in Northwest Oregon and Southwest Washington

Tornadoes in the Pacific Northwest, when compared with those east of the Rockies, are a relatively rare event. However, they do occur with some regularity, and as such warrant an examination of their history, climatology and predictability. Ascertaining the full history of tornadic storms in the Pacific Northwest is a difficult task. Storm Data, accumulated since 1950 is an excellent starting point, but published lists of tornadoes prior to 1950 are abbreviated at best. A search of local newspapers, supplemented by other sources such as the Monthly Weather Review and Climate and Crops yields a fuller record of the region’s tornadoes. The result is a more comprehensive history of tornadoes for Northwest Oregon and Southwest Washington. Included in the listing are corrections to the latitude and longitude of many of the previously published tornado touchdown locations.

Mapping of the tornadoes reveals a clear geographic distribution in the National Weather Service Portland’s forecast area that is clearly related to terrain. Possible causes for the observed distribution are discussed. While a vast majority of tornadoes in the Pacific Northwest have been classified as weak, there has been a handful of F1/EF1 through F3 tornadoes. The basic antecedent meteorological conditions for each of these storms are examined. Conditions favoring their development from synoptic patterns to buoyancy and helicity considerations are presented.