VVVV is the forecast prevailing visibility in meters, rounded down to the nearest reportable value in table 4-4-1. An obstruction-to-vision type of weather (w'w') must follow whenever the visibility is forecast at or less than 9,000 meters (6 statute miles).

When you are decoding the visibility group, you may find it easier to divide the VVVV by 16 to obtain the visibility in statute miles, than to look it up.

w'w' is the forecast weather and obstruction to vision from table 4-4-2. Up to eight letters and numbers may be used for each w'w' encoded. Normally, only one w'w' group is needed to describe the weather. If necessary to adequately describe the forecast weather, multiple weather groups may be used. For example, if you were forecasting 1/2 mile visibility in moderate snow, fog, and drifting snow, you could encode 800 weather condition can be encoded as one group, and INTER or TEMPO groups can be used to explain additional weather conditions.

When you use a change group (GRADU, to indicate an end to a weather condition or an obstruction to vision, use WX NIL in place of the w'w'.

Although not listed in table 4-4-2, all of the 40 series codes apply to fog reducing visibility to less than 1,000 meters (5/8 statute mile). Use figure 10BR when fog is forecast but the visibility will be 1,000 meters to 4,800 meters (3 statute miles), even if the sky will be obscured by the fog. If diffuse fog is forecast and the visibility is expected to be 5,000 meters (3 5/8 statute miles) or greater, use figure 05HZ for the w'w' group.

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