Plume Dynamics Drive Extreme Long-Range Spotting During California's Dixie Fire

Observations reveal extreme long-range fire spotting occurred during California's Dixie Fire. Specifically, we describe the occurrence of remarkable 9, 12, and 16 km spotting events on 16 August 2021. Radar data reveal these spot fires are linked to bent-over but deep convective plumes with plume tops reaching 10–12 km MSL. These plumes have characteristic lofting regions in the fire-generated updrafts and pyrometeor fall out locations in the downwind subsiding portion of the plume. Infrared data indicate spot fires occur along the plume's central axis. The cross winds impacting the plume rise and pyrometeor transport were ∼15 m s⁻¹, and the inferred transit time firebrands causing the longest-range spot fire is ∼18 min. We also provide photographic evidence for large, partially burned pyrometeors at a range of ∼20 km from the fire and link these data to Ka-band radar observations showing pyrometeor pulses and fall out over the observing site. The results of the study suggest that operational and research radars may be able to isolate periods conducive to long range spotting in near real-time.