<- ALTOCUMULUS 



Code 4 



M5: Thin (semi transparent) altocumulus in 

 bands or in a layer gradually spreading over 

 the sky and usually thickening as a whole; 

 it may become partly opaque or double- 

 layered. 



M5 designates one or perhaps two advanc- 

 ing layers of altocumulus, usually of irregular 

 thickness, the amount and thickness of which 

 are definitely increasing. The altocumulus 

 stretches to the horizon, at least in the direc- 

 tion from which it is advancing. 



4- ALTOCUMULUS 



Code 4 



M6: Altocumulus formed by the spreading out 

 of cumulus. 



Cumulus clouds of sufficiently great verti- 

 cal development may undergo an extension 

 of their summits while their bases may 

 gradually melt away. Sheets of altocumulus, 

 which are generally fairly thick and opaque 

 at first, are formed in this manner. They 

 have rather large elements, dark and soft; 

 later they may thin out and finally have rifts 

 in them or, at any rate, semitransparent 

 intervening spaces. 



When there is doubt as to whether a 

 spreading sheet should be termed alto- 

 cumulus or stratocumulus, it is best to code 

 4, since the cumulus clouds may then also 

 be coded 8. 



180 



H. O. 607 



