Family "C" Low Clouds: Stratocumulus (Sc), Stratus (St), Nimbostratus (Ns). Mean upper level, 

 2,000 meters, 6,500 feet; mean lower level, close to surface. 



Family "D" Clouds With Vertical Development: Cumulus (Cu), Cumulonimbus (Cb). 



Code 8 CUMULUS -> 



Ll: Cumulus with little vertical development 

 and seemingly flattened. 



These clouds occur in three forms: 



A. In a state of formation. 



B. Completely formed. 



C. Completely formed but broken up by 



the wind (fractocumulus). 



They usually have a marked diurnal 

 growth over land, developing until the middle 

 of the afternoon and decreasing later, both as 

 to amount and vertical extent. At sea and on 

 coasts, cumulus clouds often occur at night. 



The presence of even a single cumulonimbus 

 with any amount of stratocumulus, stratus, 

 or cumulus clouds will require coding. 



When the cumulus clouds begin to spread 

 out in any part of the sky, the clouds will be 

 coded 6 rather than 8, unless the spreading 

 portions form altocumulus, in which case 

 they will be coded 4 and 8. 



Fractocumulus of fine weather are detached 

 white clouds usually in an otherwise clear sky. 

 (See L7 for description of fracto cumulus of 

 bad weather.) 



'•\ 



Code 8 



CUMULUS -» 



L2: Cumulus of considerable development, gen- 

 erally towering, with or without other cumulus 

 or stratocumulus; bases all at the same level. 



These clouds are massive in appearance, 

 occasionally wind-tossed and broken, with 

 horizontal bases and very great vertical 

 development. They are sometimes in the 

 form of towers or of complex lieaps with 

 "cauliflower" formation. Tliey often have 

 caps or hoods (pileus) , wliich are distinguished 

 from the spreading tops of cumulonimbus by 

 their smoothness, sharpness, and short dura- 

 tion (a few minutes). 



(See L8 for the coding of cumulus of con- 

 siderable development and stratocumulus 

 with bases at difl"erent levels.) 



H. O. 607 



183 



