Since I was in a hurry earlier today, I guess I didn’t show you all the exact ref. I used from the NOAA website. Argue all you want and type in REDs or YELLOWs, but this is from NOAA, heard of them???
The exact website is:
www.srh.noaa.gov/ohx/dad/sfc/chapter5.pdf
if it doesn’t work let me know, but here is what you will find minus the few pictures.
5.2.3 Layer Amounts
The amount in eighths of clouds or obscurations (i.e., smoke, haze, fog, etc.) not necessarily all of the same type,
whose bases are at approximately the same level. It may be either continuous or composed of detached elements.
If the layer is on the ground, the sky cover is the eighths of the sky hidden by the phenomenon. That portion of the
surfaced-based layer through which the sky can be seen is not considered sky cover. An obscuration that hides part
of the sky is reported in both the sky condition and remarks.
Up to six layers may be reported for sky condition; reportable contractions are as follows:
Reportable Summation Amount of
Meaning
Contractions Sky Cover
VV Vertical Visibility 8/8
SKC S Ky Clear 0
FEW FEW less than 1/8 to 2/8
SCT S CaTtered 3/8 to 4/8
BKN BroKeN 5/8 to less than 8/8
OVC OVerCast 8/8
Table 5-1. Reportable Contractions for Sky Cover
5.2.4 Stratification of Sky Cover
Sky cover will be separated into layers with each layer containing clouds and/or obscurations (i.e., smoke, haze, fog,
etc.), with bases at about the same height.
5.2.5 Evaluation of Multiple Layers
Frequent observations are necessary to evaluate layers. A series of observations will often show the existence of
upper layers above a lower layer. Through thin lower layers, it may be possible to observe higher layers. Differences
in the directions of cloud movements are often a valuable aid in observing and differentiating between cloud layers,
particularly when the presence of haze, smoke, etc., increases the difficulty of evaluation. Ceiling light indications may
be used as a guide in determining the presence of multiple layers at night.
5.2.6 Evaluation of Interconnected Layers
Clouds formed by the horizontal extension of swelling cumulus or cumulonimbus, which are attached to a parent
cloud, will be regarded as a separate layer only if their bases appear horizontal and at a different level from the parent
cloud. Otherwise, the entire cloud system will be regarded as a single layer at a height corresponding to the base
of the parent cloud.
5.2.8 Summation Layer Amount
A categorization of the amount of sky cover at and below each reported layer of clouds and/or obscurations. The
summation amount for any given layer is equal to the sum of the sky cover for the layer being evaluated plus the sky
cover of all lower layers including partial obscurations. Portions of layers aloft detected through lower layers aloft
will not increase the summation amount of the higher layer. A summation amount for a layer cannot exceed 8/8ths.
When multiple layers are visible, the Sky Cover for any given layer is the total of the sky hidden by any surface-based
layer plus the amount of sky covered by all layers aloft that are below the layer being evaluated plus the layer being
evaluated.
Once you have broken the sky into separate layers, you are expected to determine the sky cover, in eighths, for each
of the layers and select a sky cover contraction to represent each layer in the report.
Always start evaluating sky cover at the lowest layer. As you evaluate the sky cover of each layer above, the amount
determined must be either equal to or more than the previously evaluated lower layer. For example, if the sky was
completely covered by clouds in four different layers and each layer by itself covered 2/8 of the sky, the sky cover
determined for each of the layers would be:
Ch. 5 Pg. 3
First layer (lowest) (200 feet) (2/8)= 2/8 sky cover (FEW)
Second layer (5,000 feet) (2/8 + 2/8)= 4/8 sky cover (SCT)
Third layer (10,000 feet) (2/8 + 4/8)= 6/8 sky cover (BKN)
Fourth layer (highest) (25,000 feet) (2/8 + 6/8)= 8/8 sky cover (OVC)
Notice that the sky cover of the highest layer is considered to be 8/8, even though (by itself) it is only covering 2/8
of the sky. The reason for this is that sky cover is always determined with respect to an observer on the ground.
The following example would be coded in Sky Condition as:
FEW002 SCT050 BKN100 OVC250
END
Although the clouds at 200 ’ aren’t a ceiling, those clouds are used in adding up to make the “ceiling” at 10,000?
Regards,
Clay
