美国航行情报汇编 AERONAUTICAL INFORMATION PUBLICATION AIP 1(172)

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30.4.1.3 Date and Time of Origin. This element is the date and time the forecast is actually prepared. The format is a two.digit date and four.digit time followed, without a space, by the letter “Z.”
30.4.1.4 Valid Period Date and Time. he UTC valid period of the forecast consists of two four.digit sets, separated by a “/”. The first four.digit set is a two.digit date followed by the two.digit beginning hour, and the second four.digit set is a two.digit date followed by the two.digit ending hour. Although most airports have a 24.hour TAF, a select number of airports have a 30.hour TAF. In the case of an amended forecast, or a forecast which is corrected or delayed, the valid period may be for less than 24 hours. Where an airport or terminal operates on a part.time basis (less than 24 hours/day), the TAFs issued for those locations will have the abbreviated statement “NIL AMD SKED AFT (closing time) Z” added to the end of the forecasts. For the TAFs issued while these locations are closed, the word “NIL” will appear in place of the forecast text. A delayed (RTD) forecast will then be issued for these locations after two complete observations are received.
30.4.1.5 Forecast Meteorological Conditions.
This is the body of the TAF. The basic format is:
Wind / Visibility / Weather / Sky Condition /
Optional Data (Wind Shear)
The wind, visibility, and sky condition elements are always included in the initial time group of the forecast. Weather is included only if significant to aviation. If a significant, lasting change in any of the elements is expected during the valid period, a new time period with the changes is included. It should be noted that with the exception of an “FM” group, the new time period will include only those elements which are expected to change; i.e., if a lowering of the visibility is expected but the wind is expected to remain the same, the new time period reflecting the lower visibility would not include a forecast wind. The forecast wind would remain the same as in the previous time period.

Any temporary conditions expected during a specific time period are included with that time period. The following describes the elements in the above format.
   a) Wind. This five (or six) digit group includes the expected wind direction (first 3 digits) and speed (last 2 digits or 3 digits if 100 knots or greater). The contraction “KT” follows to denote the units of wind speed. Wind gusts are noted by the letter “G” appended to the wind speed followed by the highest expected gust.
NOTE.
A variable wind direction is noted by “VRB” where the three digit direction usually appears. A calm wind (3 knots or less) is forecast as “00000KT.”
EXAMPLE.
18010KT . wind one eight zero at one zero (wind is blowing from 180 at 10 knots).
35012G20KT . wind three five zero at one two gust two zero
   b) Visibility. The expected prevailing visibility up to and including 6 miles is forecast in statute miles, including fractions of miles, followed by “SM” to note the units of measure. Expected visibilities greater than 6 miles are forecast as P6SM (Plus six statute miles).
EXAMPLE.
1/2SM. . . . . . . . visibility one.half 4SM . . . . . . . . . visibility four P6SM . . . . . . . . visibility more than six
   c) Weather. The expected weather phenomena is coded in TAF reports using the same format, qualifiers, and phenomena contractions as METAR reports (except UP).
Obscurations to vision will be forecast whenever the prevailing visibility is forecast to be 6 statute miles or less.
 If no significant weather is expected to occur during a specific time period in the forecast, the weather group is omitted for that time period. If, after a time period in which significant weather has been forecast, a change to a forecast of no significant weather occurs, the contraction NSW (no significant weather) will appear as the weather group in the new time period. (NSW is included only in becoming (BECMG) or temporary (TEMPO) groups.)
   d) Sky Condition. TAF sky condition forecasts use the METAR format described in the METAR section. Cumulonimbus clouds (CB) are the only cloud type forecast in TAFs.
When clear skies are forecast, the contraction “SKC” will always be used. The contraction “CLR” is never used in the aerodrome forecast (TAF).
When the sky is obscured due to a surface.based phenomenon, vertical visibility (VV) into the obscuration is forecast. The format for vertical visibility is “VV” followed by a three.digit height in hundreds of feet.
NOTE.
As in METAR, ceiling layers are not designated in the TAF code. For aviation purposes, the ceiling is the lowest broken or overcast layer or vertical visibility into a complete obscuration.
SKC “sky clear”
　
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