Leveraging Statistical and Objective Analysis to Increase Predictability of Pacific Northwest Coastal Tornadoes

An EF2 tornado which struck the town of Manzanita, Oregon on October 14^th, 2016 served as an important reminder to the risk of damaging tornadoes in all areas of the United States. There has been very little published about coastal tornadic environments in the Pacific NW, and local knowledge is primarily conceptual. However, deeper analysis suggests that predictability can be increased through further research and statistical analysis of these environments. Research led by the severe weather team at the National Weather Service (NWS) office in Portland has led to the development of situational awareness tools for these tornadic environments, based on statistical analysis, which is currently utilized by forecasters.

88 percent of all coastal tornadoes in Oregon and Washington have occurred between September 15^th and January 5^th. The timing of this “tornado season” relates to the synoptic conditions which support these environments. Destabilization is driven by cooling temperatures aloft over relatively warm ocean water and the shear is provided by the deep surface low pressure centers which are typically associated with these cold air outbreaks in the fall and early winter in the Pacific Northwest. In addition, evidence is presented for terrain induced constructive and destructive vorticity along the Oregon and Washington shores.