When a whole number and a fraction are used to forecast visibility, a space is included between them (e.g., 1 1/2SM). Visibility greater than 6 SM is encoded as P6SM.

If the visibility is not expected to be the same in different directions, prevailing visibility is used.

When volcanic ash (VA) is forecast in the significant weather group, visibility is included in the forecast, even if it is unrestricted (P6SM). For example, an expected reduction of visibility to 10 SM by volcanic ash is encoded in the forecast as P6SM VA.

Although not used by the NWS in U.S. domestic TAFs, the contraction CAVOK (ceiling and visibility OK) may replace the visibility, weather, and sky condition groups if all of the following conditions are forecast: visibility of 10 km (6 SM) or more; no clouds below 1,500 m (5,000 ft) or below the highest minimum sector altitude (whichever is greater); no cumulonimbus; and no significant weather phenomena.

Examples:

Visibility unrestricted.

Visibility 1 and ½ SM.

Visibility 4 SM.

The significant weather group (w’w’ or NSW) consists of the appropriate qualifier(s) and weather phenomenon contraction(s) or NSW (no significant weather).

If the initial forecast period and subsequent FM groups are not forecast to have explicit significant weather, the significant weather group is omitted. NSW is not used in the initial forecast time period or FM groups.

One or more significant weather group(s) is (are) included when the visibility is forecast to be 6 SM or less. The exceptions are volcanic ash (VA), low drifting dust (DRDU), low drifting sand (DRSA), low drifting snow (DRSN), shallow fog (MIFG), partial fog (PRFG), and patchy fog (BCFG). Obstructions to vision are only forecast when the prevailing visibility is less than 7 SM or, in the opinion of the forecaster, is considered operationally significant.

Volcanic ash (VA) is always forecast when expected. When VA is included in the significant weather group, visibility is included in the forecast as well, even if the visibility is unrestricted (P6SM).

NSW is used in place of significant weather only in a temporary (TEMPO) group to indicate when significant weather [including in the vicinity (VC)] included in a previous subdivided group is expected to end.

Multiple precipitation elements are encoded in a single group (e.g., -TSRASN). If more than one type of precipitation is forecast, up to three appropriate precipitation contractions can be combined in a single group (with no spaces) with the predominant type of precipitation being first. In this single group, the intensity refers to the total precipitation and can be used with either one or no intensity qualifier, as appropriate. In TAFs, the intensity qualifiers (light, moderate, and heavy) refer to the intensity of the precipitation and not to the intensity of any thunderstorms associated with the precipitation.

Intensity is coded with precipitation types (except ice crystals and hail), including those associated with thunderstorms and those of a showery nature (SH). No intensity is ascribed to blowing dust (BLDU), blowing sand (BLSA), or blowing snow (BLSN). Only moderate or heavy intensity is ascribed to a sandstorm (SS) and dust storm (DS).