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Aviation Routine Weather Report (METAR)

by Flight Learnings

in Aviation Weather Services

A METAR is an observation of current surface weather reported in a standard international format. While the METAR code has been adopted worldwide, each country is allowed to make modifications to the code. Normally, these differences are minor but necessary to accommodate local procedures or particular units of measure. This discussion of METAR will cover elements used in the United States.

Metars are issued hourly unless significant weather changes have occurred. A special METAR (SPECI) can be issued at any interval between routine METAR reports.

Example:

METAR KGGG 161753Z AUTO 14021G26 3/4SM

+TSRA BR BKN008 OVC012CB 18/17 A2970 RMK

PRESFR

A typical METAR report contains the following information in sequential order:

  1. Type of report—there are two types of METAR reports. The first is the routine METAR report that is transmitted every hour. The second is the aviation selected SPECI. This is a special report that can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information.
  2. Station identifier—a four-letter code as established by the International Civil Aviation Organization (ICAO). In the 48 contiguous states, a unique three-letter identifier is preceded by the letter “K.” For example, Gregg County Airport in Longview, Texas, is identified by the letters “KGGG,” K being the country designation and GGG being the airport identifier. In other regions of the world, including Alaska and Hawaii, the first two letters of the four-letter ICAO identifier indicate the region, country, or state. Alaska identifiers always begin with the letters “PA” and Hawaii identifiers always begin with the letters “PH.” A list of station identifiers can be found at an FSS or NWS office.
  3. Date and time of report—depicted in a six-digit group (161753Z). The first two digits are the date. The last four digits are the time of the METAR, which is always given in coordinated universal time (UTC). A “Z” is appended to the end of the time to denote the time is given in Zulu time (UTC) as opposed to local time.
  4. Modifier—denotes that the METAR came from an automated source or that the report was corrected. If the notation “AUTO” is listed in the METAR, the report came from an automated source. It also lists “AO1” or “AO2” in the remarks section to indicate the type of precipitation sensors employed at the automated station.  When the modifier “COR” is used, it identifies a corrected report sent out to replace an earlier report that contained an error (for example: METAR KGGG 161753Z COR).
  5. Wind—reported with five digits (14021) unless the speed is greater than 99 knots, in which case the wind is reported with six digits. The first three digits indicate the direction the true wind is blowing in tens of degrees. If the wind is variable, it is reported as “VRB.” The last two digits indicate the speed of the wind in knots unless the wind is greater than 99 knots, in which case it is indicated by three digits. If the winds are gusting, the letter “G” follows the wind speed (G26). After the letter “G,” the peak gust recorded is provided. If the wind varies more than 60° and the wind speed is greater than six knots, a separate group of numbers, separated by a “V,” will indicate the extremes of the wind directions. Figure 12-7 shows how the TDWR/Weather System Processor (WSP) determines the true wind, as well as gust front/wind shear location.

    Figure 12-7. Example of what the controller sees on the ribbon display in the tower cab.

    Figure 12-7. Example of what the controller sees on the ribbon display in the tower cab.

  6. Visibility—the prevailing visibility (¾ SM) is reported in statute miles as denoted by the letters “SM.” It is reported in both miles and fractions of miles. At times, runway visual range (RVR) is reported following the prevailing visibility. RVR is the distance a pilot can see down the runway in a moving aircraft. When RVR is reported, it is shown with an R, then the runway number followed by a slant, then the visual range in feet. For example, when the RVR is reported as R17L/1400FT, it translates to a visual range of 1,400 feet on runway 17 left.
  7. Weather—can be broken down into two different categories: qualifiers and weather phenomenon (+TSRA BR). First, the qualifiers of intensity, proximity, and the descriptor of the weather will be given. The intensity may be light (-), moderate ( ), or heavy (+). Proximity only depicts weather phenomena that are in the airport vicinity. The notation “VC” indicates a specific weather phenomenon is in the vicinity of five to ten miles from the airport. Descriptors are used to describe certain types of precipitation and obscurations. Weather phenomena may be reported as being precipitation, obscurations, and other phenomena such as squalls or funnel clouds. Descriptions of weather phenomena as they begin or end, and hailstone size are also listed in the remarks sections of the report. [Figure 12-8]

    Figure 12-8. Descriptors and weather phenomena used in a typical METAR.

    Figure 12-8. Descriptors and weather phenomena used in a typical METAR.

  8. Sky condition—always reported in the sequence of amount, height, and type or indefinite ceiling/height (vertical visibility) (BKN008 OVC012CB). The heights of the cloud bases are reported with a three-digit number in hundreds of feet AGL. Clouds above 12,000 feet are not detected or reported by an automated station. The types of clouds, specifically towering cumulus (TCU) or cumulonimbus (CB) clouds, are reported with their height. Contractions are used to describe the amount of cloud coverage and obscuring phenomena. The amount of sky coverage is reported in eighths of the sky from horizon to horizon. [Figure 12-9]

    Figure 12-9. Reportable contractions for sky condition.

    Figure 12-9. Reportable contractions for sky condition.

  9. Temperature and dew point—the air temperature and dew point are always given in degrees Celsius (C) or (°C 18/17). Temperatures below 0 °C are preceded by the letter “M” to indicate minus.
  10. Altimeter setting—reported as inches of mercury (“Hg) in a four-digit number group (A2970). It is always preceded by the letter “A.” Rising or falling pressure may also be denoted in the remarks sections as “PRESRR” or “PRESFR” respectively.
  11. Zulu time—a term used in aviation for UTC which places the entire world on one time standard.
  12. Remarks—the remarks section always begins with the letters “RMK.” Comments may or may not appear in this section of the METAR. The information contained in this section may include wind data, variable visibility, beginning and ending times of particular phenomenon, pressure information, and various other information deemed necessary. An example of a remark regarding weather phenomenon that does not fit in any other category would be: OCNL LTGICCG. This translates as occasional lightning in the clouds and from cloud to ground. Automated stations also use the remarks section to indicate the equipment needs maintenance.

Example:

METAR KGGG 161753Z AUTO 14021G26 3/4SM

+TSRA BR BKN008 OVC012CB 18/17 A2970 RMK

PRESFR

Explanation:

Routine METAR for Gregg County Airport for the 16th day of the month at 1753Z automated source. Winds are 140 at 21 knots gusting to 26. Visibility is ¾ statute mile. Thunderstorms with heavy rain and mist. Ceiling is broken at 800 feet, overcast at 1,200 feet with cumulonimbus clouds. Temperature 18 °C and dew point 17 °C. Barometric pressure is 29.70 “Hg and falling rapidly.

515G+mn0RuL._SX331_BO1,204,203,200_Learn more about aviation weather with Weather Flying by Robert Buck. Regarded as the bible of weather flying, this aviation classic not only continues to make complex weather concepts understandable for even the least experienced of flyers, but has now been updated to cover new advances in technology.

 

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