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  1. On 30 June 2013, 19 Granite Mountain Hotshots firefighters were killed fighting a wildfire near Yarnell in the mountains of Central Arizona. They succumbed when the wildfire, driven by erratic winds, blocked their escape route and overran their location. A previous study is extended to simulate and analyze the downscale organization of convective circulations that redirected the wildfire, which started from the scale of the Rossby Wave Breaking over North America to a convective gust front that redirected the wildfire, trapping the firefighters. Five stages are found: Stage I, the initial deep prolonged gust front; Stage II, a front-to-rear jet and its ascending motions that organized high-based convection; Stage III, high-based dry microburst-induced downdrafts organized initially by ascending flow in Stage II that transported mass and entropy to the surface; Stage IV; multiple meso-γ-scale high centers and confluence zones formed that encompassed the firefighters’ location, which established a favorable environment leading to Stage V, canyon-scale circulations formed surrounding the fire. The atmosphere thus transitioned from supporting a deep and long-lived convective density current to elevated dry microbursts with mass and wind outflow into a canyon, redirecting the ongoing wildfire. 
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  2. Abstract Numerical simulations were conducted to investigate the upstream environment’s impacts on the airflow over the lee slope of the Cuyamaca Mountains (CM) near San Diego, California, during the Cedar Fire that occurred from 25 to 29 October 2003. The upstream environment was largely controlled by a southwest–northeast-oriented upper-tropospheric jet streak that rotated around a positively tilted ridge within the polar jet stream. Three sequential dynamical processes were found to be responsible for modifying the mesoscale environment conducive to low-level momentum and dry air that sustained the Cedar Fire. First, the sinking motion associated with the indirect circulation of the jet streak’s exit region strengthened the midtropospheric flow over the southern Rockies and the lee slope of the Sawatch and San Juan Ranges, thus modestly affecting the airflow by enhancing the downslope wind over the CM. Second, consistent with the coupling process between the upper-level sinking motion, downward momentum transfer, and developing lower-layer mountain waves, a wave-induced critical level over the mountain produced wave breaking, which was characterized by a strong turbulent mixed region with a wind reversal on top of it. This critical level helped to produce severe downslope winds leading to the third stage: a hydraulic jump that subsequently enhanced the downstream extent of the strong winds conducive to the favorable lower-tropospheric environment for rapid fire spread. Consistent with these findings was the deep-layer resonance between the mountain surface and tropopause, which had a strong impact on strengthening the severe downslope winds over the lee slope of the CM accompanying the elevated strong easterly jet at low levels. 
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