Lower clouds. Group Stratus.
1. Stratus communis (Plates [37] and [41]).
In its most typical state, stratus consists of a sheet of cloud of approximately uniform thickness. The most common form, however, does vary considerably, though usually dense enough to hide the sun. Portions of such a sheet would take the same specific name, unless the portions are very small and ragged, which would be expressed by adding the word fractus. S. Com.
2. Stratus maculosus (Plate [40]).
Formed either by the appearance of cloud in lumps, which are always lenticular in shape, and ultimately join together to form a stratus, or by the break up of the typical stratus. S. Mac.
3. Stratus radius (Plate [42]). Roll cloud.
Formed during the break up of a low stratus, which separates up into a number of parallel lines of cloud. S. R.
4. Stratus lenticularis (Plate [47]). Fall cloud.
Formed by the collapse of cumulus or strato-cumulus. A cloud of evening, easily recognized as lenticular patches. S. L.
5. Strato-cumulus (Plates [38] and [39]).
A term applied to either a stratus which has thickened every here and there into cumulus, or a number of cumulus which have joined together so as to show a nearly continuous common base. S. Cu.