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Fire-generated tornadic vortices (FGTVs) linked to deep pyroconvection, including pyrocumulonimbi (pyroCbs), are a potentially deadly, yet poorly understood, wildfire hazard. In this study we use radar and satellite observations to examine three FGTV cases during high-impact wildfires during the 2020 fire season in California. We establish that these FGTVs each exhibit tornado-strength anticyclonic rotation, with rotational velocity as strong as 30 m s−1 (60 kt), vortex depths of up to 4.9 km AGL, and pyroCb plume tops as high as 16 km MSL. These data suggest similarities to EF2+ strength tornadoes. Volumetric renderings of vortex and plume morphology reveal two types of vortices: embedded vortices anchored to the fire and residing within high-reflectivity convective columns and shedding vortices that detach from the fire and move downstream. Time-averaged radar data further show that each case exhibits fire-generated mesoscale flow perturbations characterized by flow splitting around the fire’s updraft and pronounced flow reversal in the updraft’s lee. All the FGTVs occur during deep pyroconvection, including pyroCb, suggesting an important role of both fire and cloud processes. The commonalities in plume and vortex morphology provide the basis for a conceptual model describing when, where, and why these FGTVs form.

An anomalous lightning event occurred on 20–21 June 2008 in central and northern California. Most of the thunderstorms produced frequent lightning with little precipitation, resulting in over 1500 new fires. Many of these fires became large, and massive firefighting efforts continued through August in order to contain all the fires. This event was not well forecast, with only isolated lightning strikes expected. Several computer model forecast parameters pointed toward the impending lightning outbreak, including satellite and lightning observations, as well as model data from 19 June. An existing procedure to forecast dry thunderstorms showed the strong possibility of a thunderstorm outbreak over California. This procedure proved to be helpful, but has been modified to better handle moisture advection and low-level forcing, which provides a more comprehensive framework for forecasting potential dry thunderstorm outbreaks.