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visibility changes to or passes 100 feet (30 meters) unless an approach minimum exists.
4.5.6*,
4.5.9 a)*
Practices use 6−knot criterion for average wind speed to report variable wind direction in METAR
and SPECI.
4.5.9 b)* Practices define wind gust as rapid fluctuations in wind speed with a variation of 10 knots or more
between peaks and lulls. Wind speed data for the most recent 10 minutes is examined and a gust, the
maximum instantaneous wind speed during that 10−minute period, is reported if the definition
above is met during that period.
4.6.5* Practice is to report prevailing visibility. Prevailing visibility is defined as the visibility that is
considered representative of visibility conditions at the station (automated observation), or the
greatest distance seen throughout at least half the horizon circle, not necessarily continuous (manual
observation).
4.7.14* RVR values, reported in feet (FT), are based on light setting 5 (highest available) for the designated
instrument runway. RVR tendency is not reported.
4.8.2* The following weather elements are augmented manually at designated automated stations
observation sites: FC, TS, GR, GS, and VA. At selected airports, additional present weather
elements may be provided.
With the exception of volcanic ash, present weather is reported when prevailing visibility is less
than 7 statute miles or considered operationally significant. Volcanic ash is always reported when
observed.
4.8.4* The practice is to not report the following weather phenomena at unstaffed stations in METAR or
SPECI: DZ, PL, IC, SG, GR, GS, SA, DU, FU, VA, PY, PO, SQ, FC, DS, and SS.
4.8.5* The practice is to not report the following characteristics of present weather phenomena in METAR
or SPECI: SH, DR, MI, BC, and PR at unstaffed stations.
4.8.6* The practice with respect to the proximity indicator VC is between 5 to 10 statute miles from the
point of observation with the exception of precipitation for which the VC indicates 0 to 10 statute
miles from the point of observation.
31 JULY 08
AIP
United States of America
GEN 1.7−22
15 MAR 07
Nineteenth Edition Federal Aviation Administration
4.9.5* The U.S. reports only up to 3 layers at automated sites and up to 6 layers at manual sites. Cloud
layer amounts are a summation of layers at or below a given level, utilizing cumulative cloud
amount. In addition, at automated sites which are unstaffed, cloud layers about 12,000 feet are not
reported. At staffed automated sites, clouds above 12,000 feet may be augmented.
4.13.1* Practices require the inclusion of a modifier field to designate AUTO for totally ‘‘automated’’
observations (no human augmentation) or COR for corrected observations between the date and
time of the report and the surface wind direction and speed.
4.13.2 The U.S. does not use the term CAVOK in meteorological reports.
Chapter 6 Forecasts
6.2.5 b)* Change groups and amendment criteria below 1/2 statute mile (800 meters) are not used.
6.2.5 d)* The 100 foot (30 meter) change group and amendment criterion is not used.
6.2.17* Forecast visibility increments used consist of 1/4 mile from 0 (zero) to 1 mile; 1/2 mile from 1 to
2 miles; and 1 mile above 2 miles.
6.2.18* Practices require the forecast of non−convective low−level wind shear within 2,000 feet of the
ground in the Optional Group.
6.2.19* The U.S. does not use CAVOK and NSC in meteorological forecasts.
6.3*, 6.4* Landing and takeoff forecasts are provided by the TAF.
6.5* Upper winds and upper−air temperatures are not included in area forecasts.
6.6.2, 6.6.3 Area forecasts are issued three times a day in the U.S., with the exception of Alaska and Hawaii
where they are issued four times a day. They are valid for a 12−hour period beginning 1 hour after
issuance and have an 18−hour outlook.
Chapter 7 SIGMET and AIRMET Information, Aerodrome Warnings and Wind Shear Warnings
7.3.1 The U.S. does not include cloud amount or type in AIRMET.
9.6.1, 9.6.3 The U.S. does not report ISOL, OCNL, or FREQ in accordance with the guidance on the use of the
terms given in Attachment F.
*Indicates ICAO Recommended Practice
31 JULY 08
AIP
United States of America
GEN 1.7−23
15 MAR 07
Federal Aviation Administration Nineteenth Edition
ANNEX 4 − AERONAUTICAL CHARTS
Chapter 1 Definitions
Air taxiway The U.S. does not depict defined surfaces for air−taxiing of helicopters.
Danger area The term “danger area” will not be used in reference to areas within the U.S. or in any of its
possessions or territories.
Final approach
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