The Wine Country Fires of October 2017: Origins as a Highly Predictable, Terrain-Induced Downslope Windstorm

During the evening of October 8, 2017 a collection of catastrophic fires developed in the high terrain of Somona County and, driven by strong winds, descended into nearby heavily populated regions including Santa Rosa and Napa. As a result of these fires, 44 people lost their lives, approximately 9000 structures were destroyed, and total economic loss has been estimated to exceed 15 billion dollars. Winds gusting to 60-90 kts were observed downstream (southwest) of the crests of the regional domain, and appear to have both initiated (through interaction with the electrical system) and driven the wildfires that evening.

This presentation will describe the meteorology of the Wine County fires, showing that the winds were associated with strong downslope winds. Known locally as the Diablo Winds, this strong flow is connected with high pressure building into the intermountain west, which results in strong offshore pressure gradients, a stable layer near and above crest level, and a critical level above crest level. Both observations and the output of a high-resolution WRF simulation for this event will be described. The realism of current high-resolution modeling will be evaluated for this wind/firestorm, and the potential use of such modeling for reducing the impacts of such events will be examined. Finally, the climatological conditions preceding the fires will be described and the impacts of global warming will be examined.