Q1. Which two manuals contain detailed
instructions regarding the Navys surface
weather observation program?
Q2. What are the three temperature scales in use
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
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 Majestys Meteorological Office Publication 716.
Posters and charts are also available from the National
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."
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