REVIEW  QUESTIONS Q1.   Which   two   manuals   contain   detailed instructions  regarding  the  Navy’s  surface weather  observation  program? Q2.  What are the three temperature scales in use today? Q3.  Each time zone covers approximately how many degrees  of  longitude? Q4.  What does the abbreviation UTC mean? Q5.  What observation element should be observed last? SKY  CONDITION LEARNING   OBJECTIVES:   Define   sky condition and state-of-the-sky. Describe cloud form, cloud genera, cloud species, and cloud variety. Identify the 10 cloud forms and their characteristics.   Identify   significant supplemental   cloud   features.    Define orographic  clouds.  Explain  cloud  layer coverage and total sky coverage. Define cloud ceiling and explain how cloud layer height and ceiling height are measured. As an observer, your interpretation of the sky condition  may  determine  whether  a  pilot  should  fly under instrument flight rules (IFR) or visual flight rules (VFR). In some circumstances, your judgment of sky conditions might even prevent a pilot from getting off the   ground.   Sky   condition   reports   also   reflect developing weather conditions; these reports help predict weather over the next several days. The   term   sky   condition   includes   all   cloud parameters  estimated  or  measured  by  weather observers.  State-of-the-sky  is  a  specific  term  that equates to one of the 27 internationally recognized sky states. These 27 states-of-the-sky are represented by code  numbers  that  identify  the  type  of  cloud  or combinations of clouds present in the sky, and the changes in the clouds over the past few hours. Refer to Appendix IV, WMO codes 0513, 0515, and 0509. The following sections discuss the identifying features of cloud types. Both NAVMETOCCOMINST 3141.2 and NAVMETOCCOMINST 3144.1 have detailed  descriptions  of  the  27  states-of-the-sky.  Two other manuals useful in cloud identification are the International Cloud Atlas, WMO Publication 407, and the full-color edition of Cloud Types For Observers, Her Majesty’s Meteorological Office Publication 716. Posters and charts are also available from the National Weather  Service. CLOUD IDENTIFICATION SCHEME Clouds may be identified by using very general terms or very specific names. We can classify cloud identification terms from the most general to the most specific as cloud form, cloud genus, cloud species, and cloud  variety.  Some  clouds  also  prominent supplementary features that are considered either odd or significant enough to be identified with a specific name. How specific must the observer be in identifying clouds? In the METAR/SPECI code, the observer is not usually required to identify the clouds by name; only the amount of sky covered by clouds in the various cloud layers is recorded and encoded. However, certain cloud genera and supplementary features are considered significant enough to report as Remarks. In the Land and Ship Synoptic codes, the observer must identify the proper cloud genera, species, and variety in order to select the proper state-of-the-sky code. The following information on cloud identification is  presented  to  help  you  understand  the  various reportable  cloud  "types." Cloud Forms There are three different general cloud forms: cumuliform,  stratiform,  and  cirriform.  Cumuliform clouds are puffy, with distinct elements or cells. The puffy appearance of these clouds is caused by moist air rising within the cloud cell. Stratiform clouds develop in uniform layers and present a smoother appearance. Cirriform clouds are the thin, wispy, hairlike clouds. The primary factor that determines cloud form is the stability of the air. Unstable air tends to rise on its own. Stable air tends to remain at the same level in the atmosphere. And conditionally unstable air will retain its level until some force provides initial lift, and then it will continue to rise on its own. Cumuliform  clouds  form  because  moist, conditionally unstable air is initially forced upward by some lifting mechanism, and becomes unstable. The moist, unstable air cools gradually as it rises, reaches saturation, and condenses to form a visible cloud at a certain  level  in  the  atmosphere.  The  continued  addition of moist air maintains the cloud base at that certain 1-3