M. Frediani, RAL/NCAR

The firebrand spotting parameterization in WRF-ARW v4.4 implements a Lagrangian particle transport framework to advect firebrands originating in active fire gridpoints determined by WRF-Fire. Coupled with the model’s atmosphere, the parameterization identifies locations at risk of fire spotting by modeling transport and physical processes of individual firebrands. Firebrands are cyclically generated from sources along the fire front, transported with the atmospheric flow, and burnout during advection. Firebrands may burnout while in the air or land once trajectories descend below a given height threshold. Particles that land before complete burnout are accumulated in a 2-D field, which is used to inform the spatial likelihood of new fire ignitions due to spotting.

In this presentation, we demonstrate the firebrand spotting parameterization in simulations for the Marshall Fire (2021/12/30, ~11 AM MT). The Marshall fire started as a grass fire in Boulder County on a day of extremely high winds and dry vegetation. The fire reached the urban area quickly, caused the evacuation of 30,000 people, and over $500M in damages in under 6 hours.