Metars and TAFs
The knowledge tests have lots of questions of METARs and TAFs and rather than copy this information into every question, I’ve posted it here.
AVIATION ROUTINE WEATHER REPORT (METAR)
Handbook of Aeronautical Knowledge p 11-4, 11-5, 11-6
An aviation routine weather report, or 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. Example: METAR KGGG 161753Z AUTO 14021G26 3/4SM +TSRABR BKN008 OVC012CB 18/17 A2970 RMK PRESFR Atypical 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 special weather report (SPECI). This is a special report that can be given at any time to update the METARfor rapidly changing weather conditions, aircraft mishaps, or other critical information.
- 2. Station Identifier—Each station is identified by 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.” Alist of station identifiers can be found at an FSS or NWS office.
- 3. Date and Time of Report—The date and time (161753Z) are depicted in a six-digit group. The first two digits of the six-digit group 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—Modifiers denote 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. Example: METAR KGGG 161753Z COR
- 5. Wind—Winds are 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 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 (KT) 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 windspeed (G26). After the letter “G,” the peak gust recorded is provided. If the wind varies more than 60°and the windspeed is greater than 6 knots, a separate group of numbers, separated by a “V,” will indicate the extremes of the wind directions.
- 6. Visibility—The prevailing visibility (3/4 SM) is reported in statute miles as denoted by the letters “SM.” It is reported in both miles and fractions of miles. At times, RVR, or runway visual range 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—Weather can be broken down into two different categories: qualifiers and weather phenomenon (+TSRABR). 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 5 to 10 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 11-2]
- 8. Sky Condition—Sky condition (BKN008 OVC012CB) is always reported in the sequence of amount, height, and type or indefinite ceiling/height (vertical visibility). The heights of the cloud bases are reported with a three-digit number in hundreds of feet above the ground. 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 11-3]
- 9. Temperature and Dewpoint—The air temperature and dewpoint are always given in degrees Celsius (18/17). Temperatures below 0°C are preceded by the letter “M” to indicate minus.
- 10. AltimeterSetting—The altimeter setting is reported as inches of mercury 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. Remarks—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. The remarks section always begins with the letters “RMK.”
Example: METAR BTR 161753Z 14021G26 3/4SM -RABR BKN008 OVC012 18/17 A2970 RMK PRESFR Explanation: Type of Report:...............Routine METAR Location: ....................Baton Rouge, Louisiana Date: ........................16thday of the month Time: ........................1753 Zulu Modifier: ....................None shown Wind Information: ............Winds 140°at 21 knots gusting to 26 knots Visibility: ..................3/4 statute mile Weather: .....................light rain and mist Sky Conditions: ..............Skies broken 800 feet, overcast 1,200 Temperature: .................Temperature 18°C, dewpoint 17°C Altimeter: ...................29.70 in. Hg. Remarks: .....................Barometric pressure is falling.
Zulu Time—A term used in aviation for coordinated universal time
(UTC) which places the entire world on one time standard.
TERMINAL AERODROME FORECASTS (TAF)
Handbook of Aeronautical Knowledge p 11-9
Aterminal aerodrome forecast is a report established for the 5 statute mile radius around an airport. TAF reports are usually given for larger airports. Each TAF is valid for a 24-hour time period, and is updated four times a day at 0000Z, 0600Z, 1200Z, and 1800Z. The TAF utilizes the same descriptors and abbreviations as used in the METAR report. The terminal forecast includes the following information in sequential order:
- 1. Type of Report—ATAF can be either a routine forecast (TAF) or an amended forecast (TAF AMD).
- 2. ICAO Station Identifier—The station identifier is the same as that used in a METAR.
- 3. Date and Time of Origin—Time and date of TAF origination is given in the six-number code with the first two being the date, the last four being the time. Time is always given in UTC as denoted by the Z following the number group.
- 4. Valid Period Date and Time—The valid forecast time period is given by a six-digit number group. The first two numbers indicate the date, followed by the two-digit beginning time for the valid period, and the last two digits are the ending time.
- 5. Forecast Wind—The wind direction and speed forecast are given in a five-digit number group. The first three indicate the direction of the wind in reference to true north. The last two digits state the windspeed in knots as denoted by the letters “KT.” Like the METAR, winds greater than 99 knots are given in three digits.
- 6. Forecast Visibility—The forecast visibility is given in statute miles and may be in whole numbers or fractions. If the forecast is greater than 6 miles, it will be coded as “P6SM.”
- 7. Forecast Significant Weather—Weather phenomenon is coded in the TAF reports in the same format as the METAR. If no significant weather is expected during the forecast time period, the denotation “NSW” will be included in the “becoming” or “temporary” weather groups.
- 8. Forecast Sky Condition—Forecast sky con- ditions are given in the same manner as the METAR. Only cumulonimbus (CB) clouds are forecast in this portion of the TAF report as opposed to CBs and towering cumulus in the METAR.
- 9. Forecast Change Group—For any significant weather change forecast to occur during the TAF time period, the expected conditions and time period are included in this group. This information may be shown as From (FM), Becoming (BECMG), and Temporary (TEMPO). “From” is used when a rapid and significant change, usually within an hour, is expected. “Becoming” is used when a gradual change in the weather is expected over a period of no more than 2 hours. “Temporary” is used for temporary fluctuations of weather, expected to last for less than an hour.
- 10. Probability Forecast—The probability forecast is given percentage that describes the probability of thunderstorms and precipitation occurring in the coming hours. This forecast is not used for the first 6 hours of the 24-hour forecast.
PILOT WEATHER REPORTS (PIREPs)
Handbook of Aeronautical Knowledge p 11-17
Pilot weather reports provide valuable information regarding the conditions as they actually exist in the air, which cannot be gathered from any other source. Pilots can confirm the height of bases and tops of clouds, locations of wind shear and turbulence, and the location of in-flight icing. If the ceiling is below 5,000 feet, or visibility is at or below 5 miles, ATC facilities are required to solicit PIREPs from pilots in the area. When unexpected weather conditions are encountered, pilots are encouraged to make a report to an FSS or ATC. When a pilot weather reportis filed, the ATC facility or FSS will add it to the distribution system to brief other pilots and provide in-flight advisories. PIREPs are easy to file and a standard reporting form outlines the manner in which they should be filed. Figure 11-4 shows the elements of a PIREP form. Item numbers one through five are required information when making a report, as well as at least one weather phenomenon encountered. PIREPs are normally transmitted as an individual report, but may be appended to a surface report. Pilot reports are easily decoded and most contractions used in the reports are self-explanatory.
Example: UA/OVGGG 090025/ M 1450/ FL060/ TPC182/ SK 080 OVC/ WX FV04R/ TA05/ WV270030/ TB LGT/ RM HVYRAIN Explanation: Type: ..............................Routine pilot report Location: ..........................25 NM out on the 090° radial, Gregg County VOR Time: ..............................1450 Zulu Altitude or Flight Level: ..........6,000 feet Aircraft Type: .....................Cessna 182 Sky Cover: .........................8,000 overcast Visibility/Weather:.................4 miles in rain Temperature: .......................5°Celsius Wind: ..............................270°at 30 knots Turbulence: ........................Light Icing: .............................None reported Remarks: ...........................Rain is heavy.
Beginning on November 5, 2008 some larger international airports are moving to a 30 hour TAF. The weather portion remains the same. TAFs for all airports will have a small change in the date and time area to conform to ICAO standards and accommodate the change in forecast period. Details can be found on the National Weather Service site. The change appends the day to the forecast period, FM, PROB, TEMPO times. It will be a while before the change is reflected on the Knowledge Tests.
The wind direction in local reports, ATIS, ASOS, and AWOS are reported with reference to magnetic north. “Long-lines” reports, METARs, TAFs, Winds Aloft, etc. are given with reference to true north. Which makes sense when you think about it. When you’re landing, you want to know the wind direction relative to the runway. When planning flights, you don’t necessarily know the magnetic deviation of each location where you are getting wind reports, so getting the report relative to true north works best. AOPA has details.