content_image/585117.jpg content_image/585118.jpg
<img src='content_image/585117.jpg'>

<img src='content_image/585118.jpg'>

Clouds with extensive vertical development are cumulus clouds that build vertically into towering cumulus or cumulonimbus clouds, often developing into thunderstorms. The bases of these clouds form in the low to middle cloud region, but can extend into high altitude cloud levels. Towering cumulus clouds indicate areas of instability in the atmosphere, and the air around and inside them is turbulent. These clouds generally have their bases below 6,500 feet above the terrain and tops sometimes extend above 60,000 feet. Clouds with extensive vertical development are caused by lifting action, such as convective currents, orographic lift, or frontal lift. 

Scattered cumulus or isolated cumulonimbus clouds seldom present a flight problem, since these clouds can usually be circumnavigated without difficulty. However, these clouds may rapidly develop in groups or lines of cumulonimbus. They may also become embedded and hidden in stratiform clouds, resulting in hazardous flight conditions. 

Within the high, middle, and low cloud groups are two main subdivisions. These are: 

• Clouds formed when localized vertical currents carry moist air upward to the condensation level. These vertical development clouds are characterized by their lumpy or billowy appearance, and are designated cumuliform type clouds, meaning “accumulation” or “heap.” Turbulent flying conditions usually exist in, below, around, and above cumuliform clouds. 

• Clouds formed when complete layers of air are cooled until condensation takes place. These clouds are stratiform type clouds, meaning “layered out,” since they lie mostly in horizontal layers or sheets. Flight in stratiform cloud conditions is usually smooth. 

In addition to the two main subdivisions discussed above, is the word nimbus, meaning “rain cloud.” These clouds normally produce heavy precipitation, either liquid or solid. For example, a stratiform cloud producing precipitation is referred to as nimbostratus, and a heavy, swelling cumulus cloud that has grown into a thunderstorm is referred to as cumulonimbus. 

Cumulonimbus clouds contain large amounts of moisture and unstable air, and usually produce hazardous weather phenomena such as lightning, hail, tornadoes, gusty winds, and wind shear. These extensive vertical clouds can be obscured by other cloud formations and are not always visible from the ground or while in flight. When this happens, these clouds are said to be embedded, hence the term, embedded thunderstorms. 

To pilots, the cumulonimbus cloud is perhaps the most dangerous cloud type. It appears individually or in groups and is known as either an air mass or orographic thunderstorm. Heating of the air near the Earth’s surface creates an air mass thunderstorm; the upslope motion of air in the mountainous regions causes orographic thunderstorms. Cumulonimbus clouds that form in a continuous line are nonfrontal bands of thunderstorms or squall lines. 

Knowledge of principal cloud types and the factors that affect them helps the pilot visualize expected weather conditions, and to recognize potential weather hazards. 

