fair weather cumulus clouds did not appear to 

 have much movement. 



June 20 was another bad day. Altocumulus 

 castellatus clouds (often a forerunner of thunder- 

 storms and unstable air) were noticed from mid- 

 night until about 0900, but no cumulus develop- 

 ment beyond fair weather stage followed. At 

 0800 altocumulus lenticularis appeared and the 

 wind increased. At 1 1 00 the fire jumped a wide 

 control line and raced up a 90-percent slope 

 through a black spruce stand at a rate of 140 

 chains per hour. After it burned out the large 

 patch of black spruce it crept slowly in the sur- 

 rounding birch stand. This midday action was 

 the last period of rapid spread; the fire was de- 

 clared under control by midafternoon June 23. 



The entire 3-day period of record was char- 

 acterized by temperatures about 10° F. above 

 normal. Wind direction was predominantly from 

 northeast on June 18, east on June 19, south- 

 east on June 20, and east again on June 21. 

 Average cloud cover was 0.7. Gusty winds 

 caused some of the rapid advances by whipping 

 backfires across the control lines. Presence of 

 lenticular clouds on June 20 indicated high 

 winds aloft. These, coupled with the combina- 

 tion of the local general wind direction of south- 

 east and the normal afternoon tendency of wind 

 to flow up-canyon in the side draws, may have 

 helped the fire take advantage of local highly 

 flammable fuel concentrations and race through 

 these at unexpected times. 



LAKE 606 FIRE 



Thunderstorm downdrafts were the appar- 

 ent causes for short separate periods of vicious 

 behavior of this fire, which burned over 1,400 

 acres. 



The Lake 606 fire was thought to have been 

 started by lightning on June 19, 1959. It was 

 discovered the afternoon of June 20 by patrol 

 plane and was estimated to cover 30 acres. 

 Initial attack forces arrived in the early morning 

 of June 21 and soon found two fires totaling 

 100 acres; these burned together at 1400. 



Thunderheads persisted in the vicinity dur- 

 ing that afternoon. Fuel moisture of the sticks 

 and slats was 10 and 7 percent, respectively; 

 maximum temperature was 76, and the lowest 

 relative humidity was 44 percent. Wind was 



from the north or northeast except at 1600 and 

 1700, when it came from the southwest with 

 increased gustiness and velocity, up to 25 miles 

 per hour. 



The fire-behavior team mentioned it was 

 difficult at this time to tell which end of the fire 

 was the head and which was the rear. To quote 

 their 1600 report: 



About 1530 lots of unusual things 

 started happening. The wind was very 

 variable. It could sometimes change di- 

 rection completely and sometimes it 

 was at a standstill. There were some 

 whirlwinds all along the fire line . . 

 The smoke was rising fast and ex- 

 tremely high, becoming a part of a big 

 toadstool directly overhead. It was im- 

 possible to determine atmospheric 

 conditions from where we were be- 

 cause of the smoke. We did hear 

 thunder in the SE. 



At 1700 the report con+inued: 



Between 1600 and 1700 we had a 

 very unusual big blowup on the fire. 

 The smoke was rising extremely high 

 and forming a big toadstool directly 

 over the fire. The fire was completely 

 out of control, burning at rate of about 

 4 chains per minute (240 chains per 

 hour). It only burned about 30 minutes 

 at this rate. At 1640 it began to rain 

 and about 1715 the wind began to let 

 up. At the two places on the fire where 

 most of the activity was taking place 

 there was small black spruce and lots 

 of brush. The fire was sweeping through 

 the trees and leaving the tundra and 

 grass to burn later. At 1645 lightning 

 appeared in the SE. 



Rain stopped the fire at 1,400 acres. 



Atmospheric instability and thunderhead 

 downdrafts probably contributed heavily to the 

 extreme behavior of the fire. Black spruce also 

 appeared to be very conducive to crown fire 

 behavior. 



Fires behaving as this one did can easily 

 become "killers." To prevent such possible tragic 

 events a better understanding of the "whys" 

 must be learned, supervisory personnel on fires 



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