OBSERVATION OF CLOUDS FOR CODED MESSAGES 



A careful examination of this publication, "Cloud Codes" wiU show 

 the observer that the International plan of reporting clouds in synoptic 

 messages is radically different from that employed by the Weather 

 Bureau for many years in the word code. The principal difference is 

 that the Weather Bureau has heretofore based its coding on the kinds 

 or forms of clouds and their movements, whereas the International 

 Cloud Code is arranged to give information concerning states of the 

 sky which include cloud forms, indications of structure, and the 

 general evolution and organization of the clouds. 



In the International synoptic message one figure, 0-9, is included 

 for each of the three principal cloud levels. In each case, "0" signifies 

 ''no clouds." Thus there are 27 cloud code classifications, 9 for each 

 level — lower, middle, and upper — as shown in the tables on pages 19 

 and 20. 



One form of cloud may be found in several different code classifi- 

 cations. For example, in the table for lower clouds, cumulus is men- 

 tioned in the specification opposite the code figures 1, 2, 4, 7, 8, and 9. 

 These represent different stages in the evolution of the clouds or differ- 

 ent arrangements in combination with other clouds in the sky. The 

 same is true of clouds at the other levels — middle and upper — as will 

 be seen in an examination of the appropriate tables. 



Even if the observer is attempting to determine only the form of 

 cloud, a more or less continuous watch of the sky is helpful because 

 cloud forms are more easily identified when the evolution of the clouds 

 is observed. In using the International Code, it is important that 

 the evolution of the clouds and the states of the sky be care- 

 fully watched whenever possible because they are the basis of the 

 classifications. 



The states of the sky are classified with respect to the position of the 

 observer relative to the center of a disturbance. Thus the cloud ob- 

 servations, if carefully made, should give valuable supplementary in- 

 formation relative to the structure and evolution of the disturbance. 

 In order that the observer may code the cloud forms and states of the 

 sky correctly he must study the code specifications, cloud descriptions, 

 and illustrations so that he will have them clearly in mind when watch- 

 ing the evolution of clouds and making observations for coded messages. 

 The time allotted to the observation is insufficient to permit the ob- 

 server to search specifications and descriptions ; he must have all of this 

 in mind and whenever possible should also be fortified with a knowledge 

 of the development and arrangement of clouds during an adequate 

 interval (2 or 3 hours if practicable) preceding the observation. 



In the issue of instructions for observing clouds, it is fully realized 

 that many observations are talvcn in darkness without any preceding- 

 period of daylight to permit a preparatory period of observation; also, 

 that conditions may change materially just prior to an observation 



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