Forest Service scientists simulated the 2006 Esperanza Fire in Riverside County, California, with the Coupled Atmosphere-Wildland Fire Environment model to examine how dynamic interactions of the atmosphere with large-scale fire spread and energy release may affect observed patterns of fire behavior. The model simulated the meteorological flow in and near the fire, the fire's growth as influenced by gusty Santa Ana winds, and interactions between the fire and weather through fire-induced winds during the first day of burning. The simulation reproduced distinguishing features of the fire, including its overall direction and width, rapid spread west-south-westward across canyons, spread up canyons crossing its southern flank, splitting into two heading regions, and feathering of the fire line. The simulation correctly depicted the fire's location at the time of an early-morning incident involving firefighter fatalities. It also depicted periods of deep plume growth. The research results imrove understanding of deadly and unexpected fire behavior so that fighting wildfires will be less dangerous.