Explanation to some of the most common codes used in MET-reports.
TAF is the name for a forecast, and has a validity period of 6 to 24 hours, the validity is specified in each TAF. There are two types of TAFs issued for norwegian aerodromes, the most common one has the prefix (FC), but for some aerodromes there is also a TAF with considerably longer validity, this has the prefix (FT). Not all aerodromes has TAF issued, if there is no TAF for the aerodrome you are retrieving MET-info for, the output will say: TAF (FC) NOT AVAILABLE. The long TAF (FT) is only issued for a few of our aerodromes. A norwegian TAF will never contain temperature, dewpoint or QNH.
Wind is the mean values given in degrees and knots. In the case of a METAR, this is during the observation period (10 minutes). If the strongest wind during this period have been 10 knots or more stronger than the mean strength, this is called a gust, and will be put in the METAR. The wind may then be stated as 21015G25KT, meaning wind from 210 degrees, mean strength 15 knots with gust(s) of 25 knots during the last ten minutes.
If the wind strength is 2 knots or less, and the variation is more than 60 degrees the wind will be given as VRBxxKT. If the variations are more than 60 degrees, but less than 180 degrees, and the mean wind strength is 3 knots or more, the wind group in a METAR might look like this: 12012KT 030V190. This means that the mean direction of the wind is from 120 degrees, but the direction varies between 030 and 190 degrees. If the variations in the wind direction is 180 degrees or more and the mean wind strength is 3 knots or more, this is given as VRBxxKT.
Visibility is given in meters. Visibility is reported as prevailing visibility, which means the greatest visibility value which is reached within at least half the horizon circle or within at least half of the surface of the aerodrome. These areas could comprise contiguous or non-contiguous sectors. If visibility is 10 kilometers or more, the code will be 9999. When the lowest visibility is different from the prevailing visibility and 1) less than 1500 meters or 2) less than 50 per cent of the prevailing visibility , the lowest visibility observed should also be reported and its general direction in relation to the aerodrome indicated by reference to one of the eight points of the compass. (Example: 9000 4000NE, 2000 1400S)
If prevailing visibility is 10 kilometers or more , code 9999, and lower visibility is observed in another direction, this lower visibility will be reported. (Example: 9999 9000SW)
Clouds are given in groups telling you how much of the sky is covered by clouds and how high those clouds are, given in feet. Cloud type will not be indicated unless for Cumulunimbus (CB) and towering Cumulus (TCU). Cloud coverage is indicated in up to three groups, depending on coverage: (Number of cloud groups may exceed three, but only if clouds CB or TCU is observed and not included in one of the other groups). First group will always be the lowest clouds:
1st group: Lowest clouds, regardless of how much of the sky is covered
2nd group: Cloud coverage of SCT, BKN or OVC.
3rd group: Cloud coverage of BKN or OVC.
Cloud coverage is given using the following designators:
FEW: 1-2 eights coverage.
SCT: 3-4 eights coverage.
BKN: 5-7 eights coverage.
OVC: Full coverage.
If the clouds are below the aerodrome level, the height of these clouds is given as ///. FEW /// means that there are 1-2 eights of cloud below the aerodrome.
If there are ?sky clear? or no clouds below 5000ft or minimum sector altitude (MSA), no cumulonimbus or towering cumulus and the abbreviations ?CAVOK? is not appropriate, the abbreviation ?NSC ? is used.
If significant weather that may have an affect on aircraft operations are observed or expected either at the aerodrome or at a distance from the aerodrome, this will be mentioned in METAR, SPECI or TAF. The following table shows the different types of weather and prefixes used.
Weather that reduces visibility
Other weather phenomena
Moderate (no indication)
VC: Within 16 kilometers from, but not at the aerodrome.
PR: Partial, part of runway
SG: Snow grains
IC: Ice needles
PL: Ice pellets
GS: Small hail
VA: Volcanic ash
DU: Dust devils
HZ: Dry mist, haze
PO: Dust/sand swirls
FC: Funnel clouds, tornado, twister
SS: Sand storm
DR: Dust storm
A few examples:
+SHRA: Heavy showers of rain.
MIFG: Shallow fog.
FZFG Freezing fog.
PRFG: Partial fog, part of the runway is obscured by fog.
-DZRA: Light drizzle and rain
VCSH: Precipitation within 16 kilometers (but not at) the aerodrome.
A METAR contains the weather observed during the last 10 minutes prior to the observation time. If there have been precipitation since the last METAR, but not during the last 10 minutes, this will then be put in the METAR as recent (RE). RERA then means recent rain.
Trend is a short forecast given in METAR, and is used to advise expected changes within the two hours following the observation. Only approved aerodromes are allowed to use TREND in METARs. In such cases as a TREND is used in the METAR, three keywords will be used:
NOSIG: No significant change expected within the next two hours.
TEMPO indicates that there is forecast a temporary change to the weather given after the TEMPO group.
BECMG (becoming) indicates at least 50% chance of a gradual transition to longer lasting changes from the weather in the main part of the METAR.
PROB30: 30% probability of ...
PROB40: 40% probability of ...
TEMPO followed by date and a two digit validity time group indicates that there is forecast a temporary change to the weather given after the TEMPO group. TEMPO 1209/1215 thus means that on the 12th (day of a month) between 0900Z and 1500Z hours the weather is forecast to be.
BECMG (becoming) followed by date and a two digit validity time group indicates at least 50% chance of a gradual transition to longer lasting changes from the weather in the main part of the TAF.
BECMG means a change in forecast to commence at date and hours and be completed by date and hours (1912/1915). Only those elements for which a change is forecast are to be given following ?BECMG?.
FM followed by date and a four digit validity time, hours and minutes UTC (FM191230) is used to indicate a rapid change from the main part of the TAF. All the elements given before ?FM? are to be included following ?FM?
CAVOK(Clouds And Visibility OK) may be used in lieu of visibility and clouds if all of the following criteria are met:
No clouds below 5000 feet or minimum sector altitude (MSA) if MSA is higher than 5000 feet.
No CB or TCU
No significant weather, either at the aerodrome or in the vicinity
Visibility of 10 kilometers or more.
The temperature group in a METAR contains both the air temperature and the dewpoint, separated by a slash (/). Temperatures are given in whole degrees celsius. Temperatures below zero are prefixed with the letter M (minus).
QNH is an international code for the air pressure at the aerodrome reduced to sea level. In METAR this is prefixed with the letter Q if the QNH is given in hectopascal, and A if the QNH is given in inches of mercury. The norm in Norway is to give the QNH in hectopascals, and always in four digits, a QNH of 998 will then be Q0998 in a METAR.
Runway visual range is only given if the visibility and/or the RVR (Runway Visibility Range) is less than 1500 meters. The RVR is prefixed by the letter R followed by runway designator, then a slash (/) followed by the RVR in meters. The lowest value for RVR that may be stated is 50 meters, or the lowest limit for the system, if RVR is lower than that, the letter M will be used after the slash, as in this example: R36/M0050, meaning that for RWY36 the RVR is less than 50 meters.
If the RVR is more than 1500 meters, or more than the upper limit for the system used for measuring, the letter P will be used to prefix the RVR value. (Example R19/P2000, R19/P1500
If the RVR is measured by instruments, it is usually the mean RVR over ten minutes that is given. If the RVR varies during these 10 minutes, this is indicated by giving minimum and maximum values, separated by an indicator:
Example: R36/0300V750D: Runway 36 has an RVR of minimum 300 meters, maximum 750 meters, but the RVR is going down (D).
If the RVR has a tendency either up or down, or no tendency, this is notified by the use of the letters U (up), D (down) or N (no change).
Example: R01/0900U: Mean RVR of 900 meters and the RVR is improving.
If windshear is reported, it will be present in the METAR. For example, WS RWY36 means that windshear for runway 36 has been reported.
RMK(remark). After the abbreviation RMK
the observer can put useful and important information. Wind at higher levels
(mountain peaks) above the runway level will always be put after RMK
Example: RMK WIND 1200FT 12015KT=