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CHAPTER VIII. CLOUDS 



8000. GENERAL 



8010. Code numbers for cloud forms and states of the sky are described 

 in detail in International Cloud Atlas, 1956. Instructions in this chapter 

 are confined to those necessary for observing clouds with respect to their 

 amount and height of base. For easy reference by the observer, cloud 

 pictures of the principal type clouds, their definitions and respective code 

 numbers are included in WB Form 615-5. 



8100. DETERMINATION OF SKY COVER 



8110. GENERAL. "Sky cover" is a term used to denote the amount, in 

 eighths, of sky covered by clouds. The eighths of sky cover plus the eighths 

 of sky visible will always equal 1.0, that is 8/8. 



8120. SKY QUADRANTS. The sky may be regarded as divided into 

 quadrants, with the zenith regarded as the center, and the north, east, south, 

 and west compass points forming the dividing lines. Each quadrant contains 

 2/8 of the total sky. 



8121. Determine the amount of sky cover by use of quadrants as follows: 



8122. Estimate the amount covered by clouds in each quadrant. 



8123. Add the estimated amounts together. The sum of the amounts will 

 be the sky cover. 



Example: If an advancing cloud layer completely covers two quadrants 

 and scattered clouds of another type cover one- half of each of the remaining 

 two quadrants, the total sky cover is 2/8 + 2/8 + 1/8 + 1/8 or 6/8. 



8130. OBSCURED SKY. When the sky is completely obscured, other 

 than by clouds, e.g., by fog, falling snow, haze, smoke, etc., the sky is 

 classified as "obscured." However, when only a portion of the sky is ob- 

 scured, estimate the total amount of clouds on the basis of those that are 

 visible. 



8200. CLOUD HEIGHT 



8210. The height of the lowest cloud layer should be estimated after the 

 type of cloud has been determined by use of the tables in this chapter and 

 photographs in W. B. Form 615-5. Cloud definitions and photographs 

 contained in the International Cloud Atlas and WB Form 615-5 are useful 



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