Figure 23. — Areas of strongest winds (40 knots or 

 greater) at 700 mb., August 29 to September 2, 

 1967. 



mains of the trough in the west, while a tend- 

 ency for ridging appears again. The surface 

 fronts, distorted by topographic barriers and 

 perhaps other factors, have moved well to the 

 east. Light thundershowers occurred during 

 the late morning or afternoon of September 2 

 in eastern Montana, with only showers to the 

 north in Canada. 



Using the indications of the preceding 

 charts (and several not shown here), the areas 

 of strongest wind aloft, preceding and during 

 the fire run, are summarized in figure 23. A 

 speed of 40 knots (46 m-p.h.) has been 

 chosen as the lower limit for inclusion. The 

 outlined areas were defined on the basis of 

 the observed winds and the analyzed pres- 

 sure gradients. A gradual southeastward to 

 east-southeastward progression of strongest 

 wind is evident. The zone of such wind 

 passes through the northern Idaho area at 

 the time of the 2300 P.d.t. observations on 

 September 1. 



Figure 24. - Time graph of mean windspeed in the 5,000 to 7,000-ft. m.sJ. layer at Spokane and two adjacent 

 stations, August 30 to September 3, 1967. (Note that time proceeds from right to left in this and the 

 following three figures.) Wind direction in degrees is also shown for the maximum speed for each station. 



28 



