Atmospheric phenomena include all hydrometeors,
lithometeors, photo-meteors, and electrometeors and
their associated effects. As an observer, you have the
opportunity to observe and record some of these
phenomena on a daily basis; however, as an analyst you
must understand how and why these phenomena occur
and what effects they can have on naval operations.
Some phenomena have little effect on naval operations,
but others such as extensive sea fogs and thunderstorm
activity can delay or cancel operations.
characteristics of hydrometeors (precipitation,
clouds, fog, dew, frost, rime, glaze, drifting and
Hydrometeors consist of liquid or solid water
particles that are either falling through or suspended in
the atmosphere, blown from the surface by wind, or
deposited on objects. Hydrometeors comprise all forms
of precipitation, such as rain, drizzle, snow, and hail,
and such elements as clouds, fog, blowing snow, dew,
frost tornadoes, and waterspouts.
Precipitation includes all forms of moisture that fall
to Earths surface, such as rain, drizzle, snow, and hail,
etc. Dew, frost, clouds, fog, rime, glaze, spray,
Precipitation is classified according to both form
(liquid, freezing, and solid) and size (rate of fall). The
size of precipitation drops determines their rate of fall
to a large extent.
Precipitation that reaches Earths surface as water
droplets with a diameter of 0.02-inch (0.5 mm) or more
is classified as rain. If the droplets freeze on contact
with the ground or other objects, the precipitation is
classified as freezing rain. Rain falling from convective
clouds is referred to as rain showers. Showers are
usually intermittent in character, are of large droplet
size, and change rapidly in intensity.
Drizzle consists of very small and uniformly
dispersed droplets that appear to float while following
air currents. Sometimes drizzle is referred to as mist.
Drizzle usually falls from low stratus clouds and is
frequently accompanied by fog and reduced visibility.
A slow rate of fall and the small size of the droplets
(less than 0.5-mm) distinguish drizzle from rain. When
drizzle freezes on contact with the ground or other
objects, it is referred to as freezing drizzle. Drizzle
usually restricts visibility.
Snow consists of white or translucent ice crystals.
In their pure form, ice crystals are highly complex
hexagonal branched structures. However, most snow
falls as parts of crystals, as individual crystals, or more
commonly as clusters and combinations of these. Snow
occurs in meteorological conditions similar to those in
which rain occurs, except that with snow the initial
temperatures must be at or below freezing. Snow falling
from convective clouds is termed snow showers.
Snow pellets are white, opaque, round (or
occasionally conical) kernels of snow-like consistency,
0.08 to 0.2 inch in diameter. They are crisp, easily
compressible, and may rebound or burst when striking
hard surfaces. Snow pellets occur almost exclusively in
Snow grains consist of precipitation of very small,
white, opaque grains of ice similar in structure to snow
crystals. They resemble snow pellets somewhat, but are
more flattened and elongated. When the grains hit hard
ground, they do not bounce or shatter. Snow grains
usually fall in small quantities, mostly from stratus
clouds, and never as showers.