From the fire story told in the preceding 

 section, it is clear that a great deal was hap- 

 pening in a short time on the Svmdance Fire. 

 The investigating team has analyzed the fire 

 records to determine conditions such as 

 weather, rate of spread, fuel loading and con- 

 sumption, and fire intensity. For purposes of 

 comparison, some of these determinations 

 will be presented as an hourly log of the fire's 

 major run. 



WEATHER 



A detailed analysis of the atmospheric con- 

 ditions leading up to the fire and through 12 

 hours after its run was made by the meteoro- 

 logical personnel of the Fire Laboratory, Esti- 

 mated hourly free-atmosphere conditions — 

 wind, temperature, and humidity — both pre- 

 ceding and during the major run of the fire, 

 were derived for 5,000 ft. m.s.l. (Free- 

 atmosphere conditions are those which 

 would be experienced at some height above 

 the ground, removed from surface influences.) 



The account that has been given of the 

 progress of the fire has emphasized the impor- 

 tance of the weather influences and has in- 

 cluded a description of the weather preceding 

 the major outbreak of the fire. An illustrated 

 analysis of the general weather pattern associ- 

 ated with the fire is given in Appendix 2. Bi- 

 hourly reports on weather conditions during 

 the major run are given in the log. 



With regard to temperature, it should be 

 noted that the quantity of heat released by 

 the fire modified the reported temperatures 

 considerably near the ground, as evidenced by 

 small islands of desiccated foliage. On the 

 other hand, the general winds on the fire were 

 probably always lower than those calculated 

 for free-atmosphere conditions except where 

 accelerated by fire-induced forces. 



RATE OF SPREAD 



It is evident from the fire story given ear- 

 lier that the Sundance Fire spread with un- 

 usual rapidity during certain periods, slowing 

 somewhat in the intervals. In the Log (p. 13), 

 calculations for rate of spread are given for 



each hour. These are average values corre- 

 sponding to the time and distance interval 

 shovm on the foldout map. 



It is interesting that the fire-spread indices 

 based on the National Fire-Danger Rating 

 System, averaged for the stations in the area, 

 predicted actual conditions quite well. This is 

 evident from the following comparison: 



Predicted Actual 

 (0800) (1600) 



August 31 30 36 



September 1 52 64 



September 2 60 52 



FUEL LOADING AND CONSUMPTION 



The forest burned by the Sundance Fire 

 was composed of mixed conifer stands inter- 

 spersed with logged areas (fig. 10). A variety 

 of stand conditions ranging from young to 

 overmature and poorly to heavily stocked 

 existed before the bum. 



To determine fuel loading, measurements 

 were made on nearby areas comparable to 

 those burned, as well as on the burned area 

 itself. The fuel complex was considered to 

 contain three levels: ground litter, brush, and 

 crown material. 



Timber inventories for the Kaniksu Work- 

 ing Circle were used to estimate the crovm 

 fuel weight, by a method based on research 

 done by Fahnestock (3). Data from the State 

 of Idaho indicated that timber distribution on 

 private and public lands should be similar, so 

 the timber estimates based on Forest Service 

 records were applied to the whole fire area. 

 The average crown fuel load was estimated at 

 2.04 tons per acre. Field measurements 

 yielded a value of 5.25 tons per acre in a 

 heavily stocked stand. 



The brush level was estimated by field 

 sampling at a loading of 2.7 tons per acre. 

 Visual observations throughout the bum area 

 indicated the bmsh loading could have varied 

 from 1 to 20 tons per acre, but the estimated 

 average should be reasonable. 



10 



