FORMS OF CLOUDS 



31 



Cumulo-nimbus. One half to 4J miles high. Thunder cloud; 

 shower cloud. Heavy masses of clouds rising like mountains. 

 From their base generally fall local showers of rain or snow and 

 sometimes hail or sleet. The upper edges are either of compact 



FIG. 20. Cumulo-nimbus. 



Cumulus-like outline and form massive summits surrounded by deli- 

 cate false Cirrus, or the edges themselves are drawn out into Cirrus- 

 like elements. This last form is most common in spring showers. 



FIG. 21. Alto-cumulus. 



Alto-cumulus. 2 to 4 miles high. Dense, fleecy clouds. Large 

 whitish or grayish balls with shaded portions, grouped in flocks or 

 rows, frequently so close together that their edges meet. The 

 different balls are generally larger and more compact toward 



