A METAR message is valid AT the time of observation (not for any specific time period). It is an actual observation at a specific time, normally made at hourly or half hourly intervals. If weather changes by a significant degree a special observation “SPECI”, will be issued.
A ceiling is defined as, height above ground or water of the lowest layer of cloud below 20000 ft covering more than half of the sky.
In a METAR message, the wind group is 23010 MPS means wind from 230 deg true at 20 knots. Multiply MPS (metrs per second) by 2 to get the answer in Knots. Knots is double the MPS value. Met reports have wind direction in degrees “true”. ATC provides (like in ATIS) wind direction in degrees magnetic.
In the METAR code the abbreviation VC indicates “Vicinity” i.e. present weather within a range of 8 km, but not at the airport.
The visibility transmitted in a METAR is the lowest observed in a 360 deg scan from the meteorological station.
DLLO 121550Z 31018G30KT 9999 FEW060TCU BKN070 14/08 Q1016 TEMPO 4000 TS=
Above METAR cannot be abbreviated to CAVOK because the cloud base is below the highest minimum sector altitude. CAVOK only refers to ceiling and visibility.
The FEW060TCU gives cloud below the MSA and TCU, both of these preclude CAVOK.
The ICAO definition of CAVOK changed and now mentions TCU which it didn’t before. In other words, before the change you could have TCU present and it could still be CAVOK but now TCU would preclude it being CAVOK. (http://www.atpforum.eu/showthread.php?t=10747)
The definition of CAVOK will change, such that Towering Cumulus Clouds (TCU) are now regarded as significant clouds. If there are Towering Cumulus Clouds (TCU) present, CAVOK will no longer be permitted to be reported. This change will be applied on 5 Nov 2008. (http://www.caa.co.uk/docs/1382/UK%20Met%20Consultation.pdf)
When gusts are at least 10 knots above the mean wind speed then the surface wind in a METAR records a gust factor?
VV is vertical visibility in hundreds of feet and not in meters.
Trend forecast is a landing forecast appended to METAR/SPECI, valid for 2 hours.
If CAVOK is reported then there cannot be low drifting snow.
The cloud base, reported in the METAR, is the height above airfield level (i.e. AAl not AGL).
LSZH VRB02KT 5000 MIFG 02/02 Q1015 NOSIG
The report is possible, because shallow fog (MIFG) is defined as a thin layer of fog below eye level. Shallow fog is low-lying fog that does not obstruct horizontal visibility at a level 2 m (6 ft) or more above the surface of the earth (i.e. the fog layer is not deeper than 2 meters). This is, almost invariably, a form of radiation fog.
In METAR messages, the pressure group represents the QNH rounded “Down” (not Up) to the nearest hPa.
Runway report 01650428 appended to a METAR means you should consider the friction co-efficient which is 0.28 when making performance calculations. see the decode here (http://www.atpforum.eu/showthread.php?t=941)
Cloud base is reported in steps of 100 ft up to 10,000 ft and in steps of 1,000 ft above 10,000 ft in a METAR
If a large number of reports are sent as a block bulletin (in bulk) they are prefixed by the code SA (Station Actual) for METARS and SP for SPECIs. If TAF is issued in a bulletin then report type is coded as FC (9-12 hrs) or FT (12-24 hrs).
NOSIG means No Significant Change