Francisco vicinity. 



Evaluation of Results 



The fall months September, October, 

 and November show the ridge of high 

 pressure has retreated, the Aleutian 

 Low has begun to deepen, and the 

 thermal low of the southwest U.S. is 

 weakening. The weakening of the 

 thermal low also lessens the pressure 

 gradient along the California coastal 

 areas. The magnitude of the stress 

 vectors in the areas of Seattle to San 

 Diego generally reach a minimum. The 

 magnitude of the stress vectors in the 

 areas from Attu to Cordova and from 

 Sitka to Vancouver show a marked in- 

 crease during these months. 



The areas from St. Lawrence to Bar- 

 row are not discussed due to the limit- 

 ed amount of monthly coverage. 



In interpreting and using this atlas, 

 note should be taken of the source of 

 the wind data. The Naval Weather 

 Service SSMO s were compiled from 

 punched cards of weather observations 

 taken aboard ships of varying registry 

 while in passage within the various 

 areas shown in figures 37 through 39. 

 Possible bias in this data could come 

 from the tendency of ships to follow 

 certain routes, or remain close to the 

 coast, in some areas, thus making the 

 data more representative of the specific 

 route than of the area. An additional 

 bias toward good weather samples 

 would be introduced by the tendency 

 of ships to avoid bad weather when 

 possible. A final factor affecting the 

 results is the number of samples in the 

 month. An indication of the size of the 

 samples is given in Table 2 which gives 

 the number of observations reported in 

 January and in July for the various 

 areas. 



