Cloud
High clouds form at altitudes of in the polar regions, in the temperate regions and in the tropics. All cirriform clouds are classified as high and thus constitute a single genus "cirrus" (Ci). Stratocumuliform and stratiform clouds in the high altitude range carry the prefix "cirro-", yielding the respective genus names "cirrocumulus" (Cc) and "cirrostratus" (Cs). When limited-resolution satellite images of high clouds are analysed without supporting data from direct human observations, it becomes impossible to distinguish between individual forms or genus types, which are then collectively identified as "high-type" (or informally as "cirrus-type" even though not all high clouds are of the cirrus form or genus).Non-vertical clouds in the middle level are prefixed by "alto-", yielding the genus names "altocumulus" (Ac) for stratocumuliform types and "altostratus" (As) for stratiform types. These clouds can form as low as above surface at any latitude, but may be based as high as near the poles, at mid latitudes, and in the tropics. As with high clouds, the main genus types are easily identified by the human eye, but it is not possible to distinguish between them using satellite photography. Without the support of human observations, these clouds are usually collectively identified as "middle-type" on satellite images.
Low clouds are found from near surface up to . Genus types in this level either have no prefix or carry one that refers to a characteristic other than altitude. Clouds that form in the low level of the troposphere are generally of larger structure than those that form in the middle and high levels, so they can usually be identified by their forms and genus types using satellite photography alone.
Stratus cloud
Stratus nebulosus clouds appear as a featureless or nebulous veil or layer of stratus clouds with no distinctive features or structure. They are found at low altitudes, and is a good sign of atmospheric stability, which indicates continuous stable weather. Stratus nebulosus may produce light rain and drizzle or flakes of snow. Stratus fractus clouds on the other hand, appear with an irregular shape, and forms with a clearly fragmented or ragged appearance. They mostly appear under the precipitation of major rain-bearing clouds. These are the nimbostratus clouds, and the cumulonimbus clouds, and are classified as pannus clouds. Stratus fractus can also form beside mountain slopes, without the presence of nimbus clouds (clouds that precipitate), and their color can be from dark grey to almost white.