SPOKANE- PILOT BALLOON OBSERVATIONS 



AUG. 29- 30, 1967 (Pacific Standard Time) 



I/) 



4 8 12 16 20 24 



WINDSPEED (KNOTS) 

 Figure 3.— The Sundance Fire low-level jet wind. 



afternoon sounding (1600) showed the wind had died down 

 before extreme high windspeeds drove the fire northeast 

 during the major run in early September. 



SUMMARY 



It is well documented that windspeeds often increase 

 and may reach maximum values on high mountain slopes 

 during the nighttime hours. Evidence given here, including 

 published information, supports the contention that this 

 weather phenomenon is due to a low-level jet wind. 

 Blackadar's low-level jet theory (1957) can be used to help 

 predict the wind velocity during the night from initial 

 conditions. The jet wind is enhanced by the formation 

 of a surface temperature inversion and the occurrence of 

 a thermal wind component that opposes the geostrophic 

 wind. This latter condition is brought about by the 

 presence of a warm low-pressure system (or cold high- 

 pressure system). Because these nocturnal jet winds pose 

 an ever-present threat to fire management activities in 

 high mountainous areas, forecasting techniques should be 

 developed. 



PUBLICATIONS CITED 



Anderson, Hal E. 

 1968. Sundance Fire: an analysis of fire phenomena. 

 USDA For. Serv. Res. Pap. INT-56, 37 p. Intermt. For. 

 and Range Exp. Stn., Ogden, Utah. 



Barad, M. L. 



1961. Low-altitude jet streams. Sci. Am. 205(2):120-131. 

 Barrows, J. S. 



1951. Fire behavior in northern Rocky Mountain forests. 

 USDA For. Serv., North. Rocky Mt. For. and Range Exp. 

 Stn., Pap. 29, 103 p. Missoula, Mont. 



Blackadar, A. K. 

 1957. Boundary layer wind maxima and their 

 significance for the growth of nocturnal inversions. 

 Bull. Am. Meteorol. Soc. 38(5):283-290. 

 Brown, A. A., and K. P. Davis. 

 1973. Forest fire control and use, 2nd ed. 686 p. 

 McGraw-Hill, New York. 

 Buajitti, K., and A. K. Blackadar. 

 1957. Theoretical studies of diurnal wind structure 

 variations in the planetary boundary layer. Q. J. Royal 

 Meteorol. Soc. 83(358) :486-500. 

 Byram, G. M. 



1954. Atmospheric conditions related to blowup fires. 

 USDA For. Serv., Southeast For. and Range Exp. 

 Stn. Pap. 35, 34 p. Asheville, N. C. 

 Finklin, A. I. 



1973. Meteorological factors in the Sundance Fire run. 

 USDA For. Serv. Gen. Tech. Rep. INT-6, 46 p. Intermt. 

 For. and Range Exp. Stn., Ogden, Utah. 

 Gifford, F. A. 



1952. The breakdown of a low-level inversion studied 

 by means of detailed soundings with a modified 

 radiosonde. Bull. Am. Meteorol. Soc. 33:373-379. 



Gisborne, H. T. 

 1941. How the wind blows in the forests of northern 



Idaho. 12 p. USDA For. Serv., North. Rocky Mt. 



For. and Range Exp. Stn., Prog. Rep. Missoula, Mont. 

 Hayes, G. L. 



1941. Influence of altitude and aspect on daily variations 

 in factors of forest fire danger. U.S. Dep. Agric. Circ. 

 591, 38 p. Washington D. C. 

 Hess, Seymour L. 

 1959. Introduction to theoretical meteorology. 362 p. 

 Holt, Rinehart and Winston, New York. 

 Hoecker, Walter H., Jr. 



1965. Comparative physical behavior of southerly 

 boundary-layer wind jets. Mon. Weather Rev. 

 93(2):133-144. 



Lettau, Heinz H. 

 1967. Small to large-scale features of boundary layer 

 structure over mountain slopes. In Proc. of symp. 

 on mountain meteorology, p. 1-74. Colo. State Univ., 

 Atmos. Sci. Pap. 122. 

 Means, Lynn L. 

 1952. On thunderstorm forecasting in the central United 

 States. Mon. Weather Rev. 80(10):165-189. 

 Rider, L. J. 



1966. Low-level jet at White Sands missile range. 

 J. Appl. Meteorol. 5(3):283-287. 



Schroeder, M. J., and C. C. Buck. 

 1970. Fire weather. U.S. Dep. Agric. Handb. 360, 229 p. 

 Washington D.C. 

 Small, R. T. 



1957. The relationship of weather factors to the rate of 

 spread of the Robie Creek Fire. Mon. Weather Rev. 

 85(1):1-10. 



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