Weather reports

In aviation it is very important to be able to exchange weather information rapidly and unambiguously. To solve this problem, some standards have been defined by international organizations to exchange codified weather reports.

METAR

A METAR is a codified observation message indicating an airfield weather conditions observed at a given time. There are different ways of messaging weather reports, but in FlightGear METAR is used. The data is retrieved from NOAA. Such a message is established every hour.

The METAR-message can be found and set in the dialog Environment > Weather Conditions. To have the actual weather (or playing with ATC) you need to enable the Real weather fetch in the FlightGear Wizard, or set the Weather conditions to Live data in the very same dialog.

Explanation

Example:

2008/03/15 12:24	KSFO	151224Z	05012KT	10SM	SN	BKN050	02/M08	A3016	RMK AO2 SLP228	T00221083
1	2	3	4	5	6	7	8	9	10	11

1. Date
2. ICAO Identifier (4-letter)
3. Issuance Time DDHHMMz (UTC)
   • COR (CCD in Canada) if correction to observation
4. Wind
   • First 3 digits: True Wind direction or average if variable (VRB).
     • Note: If the wind direction varies 60° or more, the direction will be indicated with a V (e.g. 180V250)
   • Next 2 digits: Mean speed and units
     • KT=knots, KMH=kilometers/hour, MPS=meters/second
   • G (gust) as needed – 2 or 3 digit maximum speed
   • Calm will be indicated by 00000KT
   • Example: 18012G22KT 150V240
5. Horizontal Visibility
   • Prevailing Visibility (PV)
     • Statue miles (SM) and fractions (US & Canada only) or,
     • 4 digit minimum visibility in meters, and,
     • Lowest value and direction, as required (shown as a remark)
   • Runway Visual Range (RVR)
     • R: Runway Designator, L/R/C as needed, “/”
     • P/M: Plus/Minus (US only)
     • 4 digit value (feet/meters)
     • V (variability) with tendency U/D/N (up/down/no change)
     • Example: R18R/1200FTV/U
6. Present Weather (Constructed sequentially):
   • Intensity
   • Descriptor
   • Precipitation (Dominant type is listed first if more than one type reported)
   • Obscuration
   • Other
7. Sky Cover
   • Cloud Description
     • Amount in eights (octas)
     • SKC=Sky Clear (clear below 12,000 for ASOS/AWOS)
     • NSC=No significant clouds
     • FEW=Few (1/8 to 2/8 sky cover)
     • SCT=Scattered (3/8 to 4/8 sky cover)
     • BKN=Broken (5/8 to 7/8 sky cover)
     • OVC=Overcast (8/8 sky cover)
8. Temperature/Dewpoint (whole °C) (preceded by M=minus)
   • First 2 digits = temperature
   • Second 2 digits = dewpoint
9. Altimeter setting (QNH) and indicator (A=InHg, Q=hPa)
10. Supplementary Information
    • RE = Recent weather followed by weather codes
    • WS = Windshear, followed by:
      • TKOF/LDG (takeoff/landing)
      • RWY (2 digits runway identifier and designator L/R/C)
    • RMK = Remark
      • SLP = Sea Level Pressure
      • T00221083 (Expanded temp/dewpoint)
      • 1st, 5th digits: 0=plus, 1=minus
      • 2nd-4th digits: temp (decimal missing) (02.2)
      • 6th-8th digits: dewpoint (decimal missing) (-8.3)
11. Trend Forecast (2 hours from time of observation) (Not used in US)
    • PROB and 2 digits (30 or 40) = probability 30% or 40%
    • Used to indicate the probability of occurence of alternate element(s) or temporary fluctuations
    • Change Indicator
      • BECMG = Becoming (used where changes are expected to reach or pass through specified values
      • TEMPO = Temporary (fluctuations of less than one hour duration
      • NOSIG = No significant change
    • Forecast Wind (same as item 4)
    • Forecast Visibility (as item 5) (9999 indicates 10Kilometers vis or greater)
    • Forecast Weather (as item 6)
    • Forecast Cloud (as item 7)

TAF

In meteorology and aviation, TAF is a format for reporting weather forecast information, particularly as it relates to aviation. "TAF" is an acronym of Terminal Aerodrome Forecast or, in some countries, Terminal Area Forecast. Generally, TAF's can apply to a 9- or 12-hour forecast; some TAFs cover an 18- or 24-hour period; and as of November 5,2008, TAFs for some major airports cover 30 hours periods. The date/time group reflects the new 30 hour period in Coordinated Universal Time (UTC), as always.

Related content

Wiki articles

• Weather

Source code

• flightgear/simgear/next/simgear/environment/metar.hxx
• flightgear/simgear/next/simgear/environment/metar.cxx

External links

• Decoding a TAF