Station model
Above or below the circle for manned stations (automatic stations do not report cloud types) that indicates sky cover can lie one or more symbols indicating cloud types in any of the low, middle, and high-étages for tropospheric clouds. One predominant cloud type may be depicted for each of three étages, if known. The middle and high-étage types are depicted above the sky cover circle of the station model, while the main low-étage cloud type is indicated below the circle. Since the station model has limited room, it makes no special provision for vertical or multi-level clouds that can occupy more than one étage at a particular time. Consequently, cloud genera with significant vertical development may be coded and plotted as low or middle depending on the altitude at which they normally form. Cumulus and cumulonimbus usually form in the low étage of the troposphere and achieve vertical extent by growing upward into the middle or high étage. Conversely, nimbostratus usually forms in the middle étage of the troposphere and becomes vertically developed by growing downward into the low étage. Although the SYNOP code has no separate formal group classification for vertical or multi-level clouds, the observer procedure for selecting numerical codes is designed to give high reporting priority to those genera or species that show significant vertical development.
Dune
Five basic dune types are recognized: crescentic, linear, star, dome, and parabolic. Dune areas may occur in three forms: simple (isolated dunes of basic type), compound (larger dunes on which smaller dunes of same type form), and complex (combinations of different types). 
Barchan dunes are crescent-shaped mounds which are generally wider than they are long. The lee-side slipfaces are on the concave sides of the dunes. These dunes form under winds that blow consistently from one direction (unimodal winds). They form separate crescents when the sand supply is comparatively small. When the sand supply is greater, they may merge into barchanoid ridges, and then transverse dunes (see below).