Extreme Wildfire Environments and Their Impacts Occurring with Offshore-Directed Winds across the Pacific Coast States

Abstract

Wildfires that posed an immediate threat to life and property during the period 1933–2021 were examined across the Pacific Coast states of California, Oregon, and Washington. Such fires were identified in local, state, and federal data archives and other sources which yielded 150 events for analysis. A subset of those fires were sorted into one of two synoptic-scale patterns associated with a fall season offshore-directed and summer season non-offshore-directed low-level flow regime. Proximity analysis soundings near the offshore wind-driven wildfires frequently displayed ingredients that supported gap and mountain wave development, which were responsible for generating fast moving wildfires, long-distance spotting, and firebrand showers that resulted in loss of life and property. Paradoxically, the most extreme combinations of strong winds and low relative humidity were observed near high population centers in Southern California, yet the most destructive and deadly fires were in less populated regions of Northern California and Western Oregon. Additional analysis of 40 Fire Behavior Fuel Models data, housing development in the wildland-urban interface, and U.S. census demographic information revealed that the Northern California and Western Oregon wildfires were associated with more devastating outcomes because 1) a higher ratio of communities were intermixed with flammable fuels, 2) fire ignitions of an electrical origin occurred in wind prone corridors that were upstream from communities, and 3) communities in Northern California and Western Oregon were composed of a greater percentage of socially vulnerable people such as the elderly who were less capable of perceiving and evading intense rapidly evolving wildfires.