CUMULONIMBUS CALVUS

CUMULONIMBUS CAPILLATUS.—The presence of the anvil top (incus) with or without cirrus blow-off identifies a cumulonimbus capillatus (fig. 1-10), which is the most recognizable form of cumulonimbus. These clouds, sometimes called "anvil" clouds or "thunderheads," frequently produce thunder, lightning, surface hail, strong and gusty surface winds, and heavy rain. CUMULONIMBUS CALVUS.—A second species of cumulonimbus, the cumulonimbus calvus, lacks the familiar anvil top. Typically, it looks like an extremely large cumulus congestus cell, with less developed cumulus clouds surrounding it and appearing to form a horizontal extension from the base of the larger buildup (fig. 1-11). Although an anvil top, thunder, or lightning need not be observed, the cloud is classified by its size, development, and ominous appearance. Typically, cumulonimbus calvus cells have very dark gray bases. These clouds may later develop an anvil top to become cumulonimbus capillatus. If conditions are not favorable for continued vertical development, cumulonimbus calvus clouds may produce moderate to heavy shower activity as the upward air currents in the cloud loose intensity. REVIEW QUESTIONS Q6. How many states-of-the-sky are internationally recognized? Q7. List the three general cloud forms. Q8. Stable air is normally associated with what general cloud form? Q9. Describe the four processes that cool air by lifting. Q10. Mid-etage clouds in the temperate regions of the earth are found between what levels? Q11. Define cloud variety. Figure 1-10.—Cumulonimbus capillatus (anvil cloud—note that cirrus blow-off has not occurred. Figure 1-11.—Cumulonimbus calvus cloud. Q12. Most supplementary cloud features are associated with what type of cloud? Q13. The height of the base of cumulus clouds is directly related to what factor? Q14. What is a simple rule of thumb for classifying cumulus congestus clouds as towering cumulus? Q15. Cumulonimbus capillatus clouds are identified by what distinguishing feature? SUPPLEMENTAL FEATURES.—Many supplemental cloud features of cumulonimbus clouds indicate the stage of development or the potential severity of the “storm.” Light precipitation can begin to fall while the cloud is still increasing in size. Heavy precipitation indicates the cell has slowed or stopped increasing in height. With the beginning of heavy precipitation, the cloud base becomes rougher and less clearly defined. Smaller, ragged, or fragmented clouds are frequent under the base of the dissipating CB cell. These ragged cloud elements are the species cumulus fractus (fig. 1-12) if they are more or less in individual elements, or stratus fractus if they form a mostly continuous layer. Collectively, the layer of fragmented elements is called pannus—a supplemental cloud feature. Cumulus fractus or stratus fractus clouds, often called "scud," usually are associated with falling precipitation or found in the vicinity of numerous showers. Pannus may exhibit very rapid movement under the CB cell base, with individual elements moving in a radically different direction than that of the CB cell. For example, it would not be uncommon to see a CB cell moving toward the northeast, with a low layer of pannus moving toward the south. 1-12