KEY TO IDENTIFICATION OF CLOUD CODE TYPES 



Observers may find the forms and arrangement of clouds in the sky, 

 as classified in the codes, to be rather confusing, especially in the be- 

 ginning. The following key may be helpful in determining the code 

 numbers to use. However, the observer should not depend uponthe 

 key alone. He should make a thorough study of all the definitions 

 and classifications and have them clearly in mind, using the key only 

 as a general guide or reminder. 



The first step is to determine whether the clouds are at lower, middle, 

 or upper levels. If clouds at more than one level are present, the 

 observer should determine which clouds belong to each of the three 

 principal levels. He will then determine the code number to use in 

 each case. 



The key is therefore intended merely to supply a hint to the observer 

 who will then recall the finer distinctions of the various code types. 



Although a code number is sent for clouds at each of the three 

 principal levels, it is evident that certain combmations are rare or even 

 impossible. For example, with an extensive sheet of dense altocu- 

 mulus, M-!,^ the observer may be unable to identify the upper cloud 

 code type even if he knows that there are upper clouds. 



1 The sjmbol Mi is equivalent to Cm=7; Jh is equivalent to Ch=8; etc. 



32 



