This note extends a predictive model for estimating spot fire distance from burning trees (Albini, Frank A. 1979. Spot fire distance from burning trees-a predictive model. USDA Forest Service General Technical Report INT-56, 73 p. Intermountain Forest and Range Experiment Station, Ogden, Utah). A formula is given for the maximum firebrand lofting height by continuous flames, such as from burning piles, jackpots of woody fuel, and so forth. This height may be used directly in the algorithm detailed in the earlier work. Also, formulas and graphs are given for estimating maximum spot fire distance when the terrain downwind of the source of firebrands is covered by vegetation of low height, bare ground, or water, rather than forest. This extension is implemented by establishing an 'effective' or minimum vegetation height to be used in the formulas given in the earlier work. The effective vegetation cover height so derived depends on the firebrand initial height.
[This publication is referenced in the "Synthesis of knowledge of extreme fire behavior: volume I for fire managers" (Werth et al 2011).]