An atmospheric model, similar to ones used for weather forecasting, has been connected to a wildfire model so that heat and moisture from the fire are released into the atmosphere, creating strong winds (especially near the fireline), which then affect the spread of the fire.

Of our model's features, the ones particularly useful for fire modeling (red checks) are that it can be used in mountainous terrain, it can model atmospheric motions over a region while focussing in with high resolution on, say, one small valley, and include large-scale atmospheric motions such as cold fronts that affect fire behavior.

Atmospheric Model: checkmarks = items particularly useful for fire modeling
	3-dimensional, time dependent
	Nonhydrostatic, anelastic
	Terrain-following coordinates, vertically stretched grid
	2-way interacting nested domains
	Course grain parallelization
	Large-scale initialization of atmospheric environment using RUC, MM5, ETA, etc.
	Models formation of clouds, rain, and hail in "pyrocumulus" clouds over fires
	Short and long wave atmospheric radiation options
	Tracks smoke dispersion

The fire component of the model calculates the fire spread rate in different fuel, wind, and slope conditions, heat release into the atmosphere, and the transition of ground fires into crown fires (ones that race through the canopies of trees)

• Fire spread and burning rates are calculated using USFS equations that depend on local wind and the type;amount of fuel.
• Ground fire can dry and ignite the canopy overhead.
• Heat and moisture from the fire go into the atmospheric model.
• Coupling with atmospheric model allows us to produce the erratic and intense features of real fire.

Propagation of the fire line itself is accomplished by subdividing each atmospheric model cell into smaller fuel grid cells. When a fuel cell is ignited by contact with a neighboring burning cell, 4 tracers that outline the burning region are ignited and track the moving fireline.

• Fuel is divided into rectangular grids. When a grid of fuel is ignited, 4 tracers are created, defining what part of a fuel cell is burning.
• Fire tracers can move with the wind, back, or move normal to it.