JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
Reportable Contractions Meaning Amount of Sky Cover
SKC or CLR 1 Sky Clear 0/8
FEW 2 Few > 0/8 - 2/8
SCT Scattered 3/8 - 4/8
BKN Broken 5/8 - 7/8
OVC Overcast 8/8
VV Obscured 3 8/8 (surface based)
1. The abbreviation CLR is used at automated stations when no clouds at or below 12,000
feet are reported; the abbreviation SKC is used at manual stations when no clouds are
reported.
2. Any amount less than 1/8 is reported as FEW.
3. The last 3 digits report the height of the vertical visibility into an indefinite ceiling.
Table 5-4 — Sky Coverage Contractions
A ceiling is the height above the ground (AGL) ascribed to the lowest broken or overcast layer;
or the vertical visibility into an obscuring phenomenon (total obscuration).
Vertical visibility is the distance that can be seen directly upward from the ground into a surfacebased
obscuring phenomenon. This term is used when the celestial dome is totally hidden from
view (8/8s) by some surface based obscuration, and the reported ceiling is determined by
measuring the vertical visibility upward as seen from the ground. In this type of situation, the
base of the obscuration is less well defined, but it may still be possible to see upwards into the
moisture (or other obstruction) for a short distance. While this does constitute a ceiling, it is
sometimes referred to as an “indefinite” ceiling, and the distance that can be seen upward into
the phenomenon is then given as the vertical visibility. For example, if the sky were totally
hidden by fog which touched the ground, but a ground observer could see a weather balloon
ascend upward into the fog for 200 feet, she would report a vertical visibility of 200 feet.
It is important to realize that the vertical visibility of 200 feet in the foregoing example is very
different from a cloud ceiling of 200 feet. With a low cloud ceiling, a pilot normally can expect
to see the ground and the runway once the aircraft descends below the cloud base. However, in
the case of vertical visibility, the obscuring phenomenon also reduces the slant range visibility.
Therefore, a pilot will have difficulty seeing the runway or approach lights clearly even after
descending below the level of the reported vertical visibility.
If the weather observer on the ground is able to see part of the celestial dome or some clouds
through an obscuring phenomenon (a partial obscuration) it is reported as few, scattered, or
broken as appropriate, and assigned a height of 000 to indicate it is a surface based phenomenon.
If clouds are present, their bases and amount or coverage are also reported.
Surface based obscuring phenomena classified as few, scattered, or broken also present a slant
range visibility problem for pilots on approach for a landing but normally to a lesser degree that
when the celestial dome is completely hidden. Thus, partial obscurations are not considered
ceilings.
4-20 Version 3.2/Dec 08