Page 52 - AFMAN 15-111, 12 MAR 2019

52 AFMAN15-111 12 MARCH 2019

10.7.1.9. Unknown Precipitation (UP): A form of precipitation reported by an FBWOS
when it detects precipitation is occurring but cannot determine the type. UP is not reported
in manual or augmented observations.
10.7.2. Obscurations are a collection of particles (hydrometeors and lithometeors) in contact
with the surface or aloft and reported in the body of the observation when they are in a dense
enough concentration to be reducing visibility below 7SM.
10.7.2.1. Mist (BR): A form of obscuration composed of minute water particles or ice
crystals suspended in the atmosphere. BR is reported when visibility is greater than or equal
to 5/8SM (1000m) but less than 7SM (9999m). Mist can be distinguished from haze by
color and moisture content; when viewed against the background, mist produces a grayish
tinge.
10.7.2.2. Fog (FG): A form of obscuration composed of minute water particles suspended
in the atmosphere. FG is a denser concentration than BR and is reported when visibility is
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reduced to less than 5/8SM (1000m). When the temperature is less than 0 C and FG is
present, report as FZFG, even if ice is not accumulating on exposed surfaces. FG may also
be encoded with the descriptors VC, MI, PR, and BC.

10.7.2.3. Smoke (FU): Small particles produced by combustion that are suspended in the
air. When present may cause the sun to appear very red at sunrise and sunset and during
the daytime, can cause a reddish tinge to the background. Smoke that has traveled a great
distance from its source usually has a light grayish or bluish color and is evenly distributed
in the air.
10.7.2.4. Volcanic Ash (VA): Fine particles of rock powder that have erupted from a
volcano and remain suspended in the atmosphere for long periods of time. Volcanic Ash
will always be reported in the body of the observation when observed, regardless of the
visibility and vicinity to the station. (T-1).

10.7.2.5. Widespread Dust (DU): Solid materials suspended in the atmosphere in the form
of small irregular particles, many of which are microscopic in size. When lifted to high
enough levels in the atmosphere, dust may travel and be observed as it settles at locations
significantly far from the original source region.
10.7.2.6. Sand (SA): Sand particles picked up from the surface of the earth by the wind,
reducing the horizontal visibility.

10.7.2.7. Haze (HZ): Extremely small, dry particles suspended in the air in sufficient
enough numbers to reduce visibility. May be distinguished from mist by color and moisture
content; when viewed against a dark background, produces a bluish tinge and when viewed
against a light background, appears as a yellowish veil.
10.7.2.8. Spray (PY): Water droplets displaced by the wind from a body of water,
generally from the crests of waves, and carried up into the air in such quantities that they
reduce the horizontal visibility. When observed to be reducing visibility, spray is always
reported as blowing (BLPY).