N_SCCh_Sh_Sh_S is the forecast cloud layer group. This group may be repeated as often as necessary in each section of the forecast to describe all the cloud layers forecast. The groups are arranged in ascending order from the lowest to the highest. When skies are forecast to be clear, encode SKC (for sky clear in place of this group. The coding of each of the three elements that make up this group is as follows:

N_S is the amount of the cloud in the layer, in eighths. The summation principle does not apply. You may, for instance, forecast a low over-cast (8 eighths) with another overcast layer (8 eighths) on top of that and a broken layer (5 eighths) above that one, for a total of 21 eighths.  

CC is the forecast cloud type. Use table 4-4-3 for the two-letter code for the cloud type.  

h_Sh_Sh_S is the forecast height of the cloud base above the surface (AGL), in hundreds of feet. Cloud bases are forecast to the nearest 100 feet from the surface to 5,000 feet; to the nearest 500 feet between 5,000 feet and 10,000 feet; and to the nearest 1,000 feet above 10,000 feet. For example, a cloud base forecast at 400 feet would be encoded as 004, while a cloud base forecast at 6,500 feet would be encoded as 065.

The ceiling is defined as the layer at which clouds at and below the layer cover more than 4 eighths of the sky. Whenever a forecast layer constitutes a ceiling, identify that layer as a ceiling by adding the group CIGh_Sh_Sh_S in the remarks section of that portion of the forecast. Always include this group for a total obscuration. When the forecast total cloud amount is more than 4 eighths, but will not constitute a ceiling, use the term CIGNO in the remarks section. For example, this would be the case when forecasting 4 eighths of cumulus at 2,500 feet and 6 eighths

of thin cirrostratus at 30,000 feet. Thin layers, or the portion of a layer that is thin, are not considered when designating a ceiling. In another situation, you may forecast several opaque layers of clouds that may each total 4 eighths, but are vertically stacked and together do not cover 5 eighths or more of the total dome of the sky, so no ceiling would be present.

You may forecast several different types of clouds with bases at the same level. Normally, encode only the predominant cloud as the cloud type, and use the total cloud coverage at that level for the cloud amount. The exception to this is

if the layer is composed of mixed cloud types which include cumulonimbus, such as 3 eighths of cumulus at 2,000 feet, 2 eighths of stratocumulus at 2,000 feet, and 1 eighth of cumulonimbus at 2,000 feet. When this situation occurs, encode cumulonimbus separately as the first group, and the total of the other cloud(s) next. Using this as an example, we would encode ICB020 5CU020.

When the sky will be totally obscured by a phenomena such as fog or precipitation, encode N_S as 9, CC as //, and h_Sh_Sh_S as the vertical visibility in hundreds of feet. For example, an obscuration at 200 feet caused by snow would be encoded as 9//002, and CIG002 would be used in the remarks section.

Although there is no direct provision in the TAF code for forecasting partial obscurations, you should indicate them by using an N_SCCh_Sh_Sh_S group in the remarks section. For example, if 5 eighths of the sky is forecast to be obscured by fog, we would use 5FG/// in the remarks section. The obscuring phenomena should be the same as the one used to forecast the restriction to visibility. When used, this remark will immediately follow any CIGh_Sh_Sh_S remark; otherwise, it should be the first remark. In this example, the fog covers more than 4 eighths of the sky, so it would be designated as a ceiling and we would encode CIG005 5FG/// as the first two entries in the remarks section.

When the total cloud amount is forecast to be less than 4 eighths but the partial obscuration will cause the total sky cover to be greater than 5 eighths, then the first layer of clouds, which, when added to the partial obscuration, totals 5 eighths or more, should be designated as the ceiling. For example, mist is forecast to reduce the visibility to 2,000 meters and will cause a partial obscuration of 3 eights of the sky, but the only cloud forecast is 2 eighths of stratocumulus at 2,500 feet (and the minimum altimeter forecast is 30.25 inches) you would encode 2000 10BR 2SC025 QNH30251NS CIG025 3BR///.

When you forecast two or more significant sky conditions that will alternate frequently, such as 3 eighths of clouds at a level alternating with 5 eights of clouds at that level, or 5 eights of cloud frequently alternating between 3,000 feet and 2,500 feet, use an INTER group (for intermittent conditions) in remarks to describe the situation. Do not use the term VRBL or V (for variable conditions) to describe any sky conditions in the TAF code.

If thunderstorms or cumulonimbus clouds are not forecast at the station but may affect aircraft approaching, departing, or operating in the vicinity of the station, you should include an appropriate remark in the remarks section to describe the situation, such as TS VCNTY or CB OMTNS W.

Although you may receive TAF forecasts from outside CONUS that include the group CAVOK, meaning ceiling and visibility OK (the visibility below 1,500 meters; no cumulonimbus clouds at any height; and there is no precipitation, ground fog, or drifting/blowing snow), in place of both the visibility (VVVV) and the cloud layer N_SCCh_Sh_Sh_S groups, this term is not an acceptable entry for use by forecasters within the continental United States. Overseas U.S. military personnel may use the term if allowed by the host countrys regional regulations. The term CAVU, meaning ceiling and risibility unlimited (visibility greater than 10 statute miles and no ceiling lower than 10,000 feet) is a term that is no longer allowed for use by any WMO member nation.

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