southeast at 14 m. p. h. at 3,000 feet, to southwest at 19 m. p. h. at 

 13,000 feet. This would indicate that, whereas the low pressure 

 at the surface is centered to the southwest of Fairbanks, at 13,000 

 feet the lower pressures are found to the northwest. 



In summer high pressures replace the low pressures of winter 

 in the Gulf of Alaska and the warmed Alaskan interior produces a 

 thermal low. The net result produces decreasing pressures across 

 Alaska toward the north. The pressure system also does not 

 change as much with elevation as at other seasons. Consequently, 

 there is no great turning of the wind with increasing elevation. 

 Prevailing winds at Fairbanks in summer, therefore, are south- 

 westerly at about 16 m. p. h. at all levels. This is slightly less 

 than the average at other seasons. 



The progression from summer to autumn brings the greatest 

 change at the 3,000-foot level with a shift of the prevailing wind 

 direction from southwest to southeast and a slight increase in 

 velocity from 14 m. p. h. in summer to 17 m. p. h. in autumn. 

 While there is practically no change in direction in the 6,000 to 

 13,000-foot layer, there is a slight increase in velocity from 16 to 

 20 m. p. h. for the prevailing southwesterly wind. It can be said 

 that the greatest seasonal variation in the wind at Fairbanks takes 

 place below 6,000 feet, with little change above that level. This 

 would indicate that mean surface pressure changes from season to 

 season, although well pronounced, are not reflected to any height 

 and that the relative pressure distribution above 6,000 feet is 

 rather constant throughout the year. 



WINTER WINDS AT POINT BARROW 



Winter winds at Point Barrow are almost entirely dominated by 

 the Polar Anticyclone. Northeast to east winds prevail up to at 

 least 13,000 feet. However, the frequency percentage decreases 

 with height from 48 percent at the surface to 30 percent at 13,000 

 feet. The average surface velocity is 14 m. p. h. From 3,000 to 

 13,000 feet the average velocity remains about 27 m. p. h. for these 

 east to northeast winds. The change from winter to spring causes 

 the winds aloft at Barrow to veer about 22° with little change in 

 surface wind direction. The velocity likewise does not vary 

 greatly from winter to spring except that, whereas in winter there 

 is slight increase in velocity for the prevailing direction from 25 

 m. p. h. at 3,000 feet to 29 m. p. h. at 10,000 feet, there is a slight 

 decrease in the velocity with elevation in the spring. 



104 



