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sensor if the report is fully automated (inwhich case the abbreviationAUTO
is also included in themessage).When the data has beenobtained fromonly
one sensor, the datawill be followed byNDV to indicate that no directional
variation can be reported (manual observations of visibilitywill include, when
certain criteria aremet, a directional variation in addition to the prevailing
visibility).
Note: Pilots should exercise cautionwhen interpreting automated visibility
information as itmay not be equivalent to a humanobservation
because:
• the information is reported as a tenminute average; and
• as it is sourced from a single instrument sampling only a very small parcel
of the atmosphere, itmay not be representative of theentire airport.
Fully automatedAWSmay issue special reports (SPECI) for visibility using
data from visibility sensors.
RunwayVisual Range (RVR)
RVR at the runway’s touchdown zonemay be reported inSPECImessages
from aerodromeswithRVR instrumentation. Itwill be reported in the format
RDD/VVVVi or RDD/VVVVVVVVVi whereR andV arefixed indicators, DD
gives the runway number, VVVV gives theRVR value and i gives the tendency
(either U, D or N for up, down or nil).WhenRDD/VVVV is reported, VVVV
is the 10-minute average. RDD/VVVVVVVVV is reportedwhen theRVRhas
varied significantly during the averaging period. The groupgives the one-
minutemeanminimum value followedby V followedby theone-minutemean
maximum value during the averaging period.
PresentWeather
PresentWeather is given using the codes listedon page 125.
Ifmore thanone form of precipitation is observed, the appropriate letter
abbreviations shall be combined in a single groupwith the first being the
dominant type of precipitation. In such a group, the intensity shall refer to the
total precipitation.
Up to three groupsmay be given.
The intensity of precipitation, blowing dust, sand or snow, dust storm and
sand stormwill be indicated by the prefix (-) for light, (+) for heavy, andno
prefix formoderate.
aerodrome forecasts and reports
2 – me t eorology