Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 2: Aviation Weather Product Classification and Policy Page 2-3
Commercial weather information providers contracted by the FAA to provide weather observations (e.g., contract towers) are included in the federal government category of approved sources by virtue of maintaining required technical and quality assurance standards under FAA and NWS oversight.
2.3.2 Enhanced Weather Information System (EWINS) EWINS is an FAA-approved proprietary system for tracking, evaluating, reporting, and forecasting the presence or absence of adverse weather phenomena. EWINS is authorized to produce flight movement forecasts, adverse weather phenomena forecasts, and other meteorological advisories.
To receive FAA approval, EWINS-approved source must have sufficient procedures, personnel, and communications and data processing equipment to effectively obtain, analyze, and disseminate aeronautical weather data. For a full explanation of the requirements for EWINS approval, see the Flight Standards Information Management System, Order 8900.1, volume 3, chapter 26, section 5. An EWINS-approved source may produce weather analyses and forecasts based on meteorological observations provided by the federal government. Approval to use EWINS weather products is issued on a case by case basis and is currently only applicable to FAR part 121 and 135 certificate holders, who may either act as their own EWINS or contract those services from a separate entity. For these approved users, the weather analyses and forecasts produced by their approved EWINS are considered primary weather products as defined in paragraph 2.1.1, Primary Weather Products.
2.3.3 Commercial Weather Information Providers Commercial weather providers are a major source of weather products for the aviation community. In general, they produce proprietary weather products based on NWS products with formatting and layout modifications but no material changes to the weather information itself. This is also referred to as “repackaging.”
Commercial providers may also produce forecasts, analyses, and other proprietary weather products and substantially alter the information contained in NWS-produced products. Hence, operators and pilots contemplating using such services should request and/or review an appropriate description of services and provider disclosure. This should include, but is not limited to,
the type of weather product (e.g., current weather or forecast weather), the currency of the product (i.e., product issue and valid times), and the relevance of the product.
Pilots and operators should be cautious when using unfamiliar products, or products not supported by FAA/NWS technical specifications. Commercially-available proprietary weather products that substantially alter NWS-produced weather products, or information, may only be approved for use by part 121 or part 135 operators or fractional ownership programs if the commercial provider is EWINS-qualified (see paragraph 2.3.2, above). Government products that are only repackaged and not altered, or products produced by EWINS-approved source, are considered primary weather products as defined in paragraph 2.2.1, Primary Weather Products.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 3: Observed Text Products Page 3-1 3 OBSERVED TEXT PRODUCTS
3.1 Aviation Routine Weather Reports (METAR) and Aviation Selected Special Weather Reports (SPECI) Surface weather observations are fundamental to all meteorological services. Observations are the basic information upon which forecasts and warnings are made in support of a wide range of weather sensitive activities within the public and private sectors, including aviation.
Although the METAR/SPECI code is used worldwide, each country is allowed to make modifications or exceptions to the code for use in their particular country. This section will focus on the U.S. modifications and exceptions. METAR/SPECIs are available online at:
http://adds.aviationweather.gov/metars/
3.1.1 Aviation Routine Weather Report (METAR) Aviation Routine Weather Report (METAR) is the primary observation code used in the U. S. to satisfy World Meteorological Organization (WMO) and International Civil Aviation Organization (ICAO) requirements for reporting surface meteorological data. A METAR report includes the airport identifier, time of observation, wind, visibility, runway visual range, present weather phenomena, sky conditions, temperature, dew point, and altimeter setting. Excluding the airport identifier and the time of observation, this information is collectively referred to as “the body of the report.” As an addition, coded and/or plain language information elaborating on data in “the body of the report” may be appended to the end of the METAR in a section coded as “Remarks.” The contents of the “Remarks” section vary with the type of reporting station. The METAR may be abridged at some designated stations only including a few of the mentioned elements.
3.1.2 Aviation Selected Special Weather Report (SPECI) An Aviation Selected Special Weather Report (SPECI) is an unscheduled report taken when any of the criteria given in Table 3-1 are observed during the interim period between the hourly reports. SPECI contains all data elements found in a METAR plus additional plain language information which elaborates on data in the body of the report. All SPECIs are made as soon as possible after the relevant criteria are observed.
Whenever SPECI criteria are met at the time of the routine METAR, a METAR is issued.
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Table 3-1. SPECI Criteria 1 Wind Shift Wind direction changes by 45 degrees or more in less than 15 minutes and the wind speed is 10 knots or more throughout the wind shift.
2 Visibility Surface visibility as reported in the body of the report decreases to less than, or if below, increases to equal or exceed:
a. 3 miles
b. 2 miles
c. 1 mile
d. The lowest standard instrument approach procedure minimum as published in the National Ocean Service (NOS) U.S Instrument Procedures. If none published use ½ mile.
3 Runway Visual Range (RVR) The highest value from the designated RVR runway decreases to less than, or if below, increases to equal or exceed 2,400 feet during the preceding 10 minutes.
U.S. military stations may not report a SPECI based on RVR.
4 Tornado, Funnel Cloud, or Waterspout
a. is observed.
b. disappears from sight, or ends.
5 Thunderstorm a. begins (a SPECI is not required to report the beginning of a new thunderstorm if one is currently reported).
b. ends.
6 Precipitation a. hail begins or ends.
b. freezing precipitation begins, ends, or changes intensity.
c. ice pellets begin, end, or change intensity 7 Squalls When they occur 8 Ceiling The ceiling (rounded off to reportable values) forms or dissipates below, decreases to less than, or if below, increases to equal or exceed:
a. 3,000 feet.
b. 1,500 feet
c. 1,000 feet
d. 500 feet
e. The lowest standard instrument approach procedure minimum as published in the National Ocean Service (NOS) U.S Instrument Procedures. If none published, use 200 feet.
9 Sky Condition A layer of clouds or obscurations aloft is present below 1,000 feet and no layer aloft was reported below 1,000 feet in the preceding METAR or SPECI.
10 Volcanic Eruption When an eruption is first noted 11 Aircraft Mishap Upon notification of an aircraft mishap, unless there has been an intervening observation 12 Miscellaneous Any other meteorological situation designated by the responsible agency of which, in the opinion of the observer, is critical.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 3: Observed Text Products Page 3-3
3.1.3 Format
Figure 3-1. METAR/SPECI Coding Format
A METAR/SPECI (Figure 3-1) has two major sections: the Body (consisting of a maximum of 11 groups) and the Remarks (consisting of 2 categories). Together, the body and remarks make up the complete METAR/SPECI. When an element does not occur, or cannot be observed, the corresponding group is omitted from that particular report.
3.1.3.1 Type of Report
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
The type of report, METAR or SPECI precedes the body of all reports.
3.1.3.2 Station Identifier
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
The station identifier, in ICAO format, is included in all reports to identify the station to which the coded report applies.
The ICAO airport code is a four-letter alphanumeric code designating each airport around the world. The ICAO codes are used for flight planning by air traffic controllers and airline operation departments. These codes are not the same as the International Air Transport Association (IATA) codes encountered by the general public used for reservations, baggage handling and in airline timetables. ICAO codes are also used to identify weather stations located on- or offairport.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Page 3-4 Section 3: Observed Text Products Unlike the IATA codes, the ICAO codes have a regional structure. For example, the first letter is allocated by continent (Figure 3-2), the second is a country within the continent; the remaining two are used to identify each airport.
Figure 3-2. ICAO Continent codes
In the contiguous U. S., ICAO station identifiers are coded K followed by the three-letter IATA identifier. For example, the Seattle, Washington (IATA identifier SEA) becomes the ICAO identifier KSEA.
ICAO station identifiers in Alaska, Hawaii, and Guam begin with the continent code P, followed by the proper country code (A, H, and G respectively), and the two-letter airport identifier.
Examples:
PANC Anchorage, AK PAOM Nome, AK PHNL Honolulu, HI PHKO Keahole Point, HI PGUM Agana, Guam PGUA Anderson AFB, Guam
Canadian station identifiers begin with C, followed by the country code, and the two-letter airport identifier.
Examples:
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 3: Observed Text Products Page 3-5 CYYZ Toronto, Canada CYYC Calgary Canada CYQB Quebec, Canada CYXU London, Canada CZUM Churchill Falls, Canada
Mexican and western Caribbean station identifiers begin with M, followed by the proper country code and two-letter airport identifier.
Examples:
MMMX Mexico City, Mexico MUGM Guantanamo Bay, Cuba MDSD Santo Domingo, Dominican Republic MYNN Nassau, Bahamas
Eastern Caribbean station identifiers begin with T, followed by the proper country code, and airport identifier.
Examples:
TJSJ San Juan, Puerto Rico TIST Saint Thomas, Virgin Islands
For a list of Alaskan, Hawaiian, Canadian, Mexican, Pacific, and Caribbean ICAO identifiers see FAA Order 7350.7. For a complete worldwide listing, see ICAO Document 7910, “Location Indicators.” Both are available on-line.
3.1.3.3 Date and Time of Report
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
The date and time is coded in all reports as follows: the day of the month is the first two digits
(01) followed by the hour (19), and the minutes (55). The coded time of observations is the actual time of the report or when the criteria for a SPECI is met or noted. If the report is a correction to a previously disseminated report, the time of the corrected report is the same time used in the report being corrected. The date and time group always ends with a Z indicating Zulu time (or UTC). For example, METAR KOKC 011955Z would be disseminated as the 2000 hour scheduled report for station KOKC taken on the 1st of the month at 1955 UTC.
3.1.3.4 Report Modifier (As Required)
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
The report modifier, AUTO, identifies the METAR/SPECI as a fully automated report with no human intervention or oversight. In the event of a corrected METAR or SPECI, the report modifier, COR, is substituted for AUTO.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Page 3-6 Section 3: Observed Text Products
3.1.3.5 Wind Group
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
Wind is the horizontal motion of air past a given point. It is measured in terms of velocity, which is a vector that includes direction and speed. It indicates the direction the wind is coming FROM.
In the wind group, the wind direction is coded as the first three digits (220) and is determined by averaging the recorded wind direction over a 2-minute period. It is coded in tens of degrees relative to true north using three figures. Directions less than 100 degrees are preceded with a
0. For example, a wind direction of 900 is coded as 090.
Immediately following the wind direction is the wind speed coded in two or three digits (15).
Wind speed is determined by averaging the speed over a 2-minute period and is coded in whole knots using the units, tens digits and, when required, the hundreds digit. When wind speeds are less than 10 knots, a leading zero is used to maintain at least a two digit wind code. For example, a wind speed of 8 knots will be coded 08KT. The wind group is always coded with a KT to indicate wind speeds are reported in knots. Other countries may use kilometers per hour (KPH) or meters per second (MPS) instead of knots.
Examples:
05008KT Wind 50 degrees at 8 knots 15014KT Wind 150 degrees at 14 knots 340112KT Wind 340 degrees at 112 knots
3.1.3.5.1 Wind Gust Wind speed data for the most recent 10 minutes is examined to evaluate the occurrence of gusts. Gusts are defined as rapid fluctuations in wind speed with a variation of 10 knots or more between peaks and lulls. The coded speed of the gust is the maximum instantaneous wind speed.
Wind gusts are coded in two or three digits immediately following the wind speed. Wind gusts are coded in whole knots using the units, tens, and, if required, the hundreds digit. For example, a wind out of the west at 20 knots with gusts to 35 knots would be coded 27020G35KT.
3.1.3.5.2 Variable Wind Direction (speed 6 knots or less) Wind direction may be considered variable when, during the previous 2-minute evaluation period, the wind speed was 6 knots or less. In this case, the wind may be coded as VRB in place of the 3-digit wind direction. For example, if the wind speed was recorded as 3 knots, it would be coded VRB03KT.
3.1.3.5.3 Variable Wind Direction (speed greater than 6 knots) Wind direction may also be considered variable when, during the 2-minute evaluation period, it varies by 60 degrees or more and the speed is greater than 6 knots. In this case a variable wind direction group immediately follows the wind group. The directional variability is coded in a clockwise direction and consists of the extremes of the wind directions separated by a V. For
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 3: Observed Text Products Page 3-7 example, if the wind is variable from 180º to 240º at 10 knots, it would be coded 21010KT 180V240.
3.1.3.5.4 Calm Wind When no motion of air is detected, the wind is reported as calm. A calm wind is coded as 00000KT.
3.1.3.6 Visibility Group
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
Visibility is a measure of the opacity of the atmosphere.
Prevailing visibility is the reported visibility considered representative of recorded visibility conditions at the station during the time of observation. It is the greatest distance that can be seen throughout at least half of the horizon circle, not necessarily continuous.
Surface visibility is the prevailing visibility from the surface at manual stations or the visibility derived from sensors at automated stations.
The visibility group is coded as the surface visibility in statute miles. A space is coded between whole numbers and fractions of reportable visibility values. The visibility group ends with SM to indicate that the visibility is in statute miles. For example, a visibility of one and a half statute miles is coded 1 1/2SM. Other countries may use meters (no code).
Automated stations use an M to indicate “less than.” For example, M1/4SM means a visibility of less than one-quarter statute mile.
3.1.3.7 Runway Visual Range (RVR) Group
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
The runway visual range (RVR) is an instrument-derived value representing the horizontal distance a pilot may see down the runway.
RVR is reported whenever the station has RVR equipment and prevailing visibility is 1 statute mile or less and/or the RVR for the designated instrument runway is 6,000 feet or less.
Otherwise the RVR group is omitted.
Runway visual range is coded in the following format: the initial R is code for runway and is followed by the runway number. When more than one runway is defined with the same runway number a directional letter is coded on the end of the runway number. Next is a solidus /;
followed by the visual range in feet and then FT completes the RVR report. For example, an RVR value for Runway 01L of 800 feet would be coded R01L/0800FT. Other countries may use meters.
RVR values are coded in increments of 100 feet up to 1,000 feet, increments of 200 feet from 1,000 feet to 3,000 feet, and increments of 500 feet from 3,000 feet to 6,000 feet. Manual RVR
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Page 3-8 Section 3: Observed Text Products is not reported below 600 feet. At automated stations, RVR may be reported for up to four designated runways.
When the RVR varies by more than one reportable value, the lowest and highest values will be shown with V between them indicating variable conditions. For example, the 10-minute RVR for runway 01L varying between 600 and 1,000 feet would be coded R01L/0600V1000FT.
If RVR is less than its lowest reportable value, the visual range group is preceded by M. For example, an RVR for runway 01L of less than 600 feet is coded R01L/M0600FT.
If RVR is greater than its highest reportable value, the visual range group is preceded by a P.
For example, an RVR for runway 27 of greater than 6,000 feet will be coded R27/P6000FT.
3.1.3.8 Present Weather Group
METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132
Present weather includes precipitation, obscurations, and other weather phenomena. The appropriate notations found in Table 3-2 are used to code present weather.
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Section 3: Observed Text Products Page 3-9
Table 3-2. METAR/SPECI Notations for Reporting Present Weather1
QUALIFIER WEATHER PHENOMENA
INTENSITY OR
PROXIMITY
DESCRIPTOR PRECIPITATION OBSCURATION OTHER 1 2 3 4 5
- Light MI Shallow DZ Drizzle BR Mist PO Dust/Sand whirls
Moderate2 PR Partial RA Rain FG Fog SQ Squalls
+ Heavy BC Patches SN Snow FU Smoke FC Funnel Cloud, Tornado, or Waterspout4
VC In the Vicinity3 DR Low Drifting SG Snow Grains VA Volcanic Ash SS Sandstorm BL Blowing IC Ice Crystals (Diamond Dust)
DU Widespread Dust DS Duststorm SH Shower(s) PL Ice Pellets SA Sand
TS Thunderstorms GR Hail HZ Haze
FZ Freezing GS Small Hail and/or Snow Pellets
PY Spray UP Unknown Precipitation
1. The weather groups are constructed by considering columns 1 to 5 in the table above in sequence,
i.e., intensity followed by description, followed by weather phenomena, e.g., heavy rain shower(s) is coded as +SHRA.
2. To denote moderate intensity no entry or symbol is used.
3. See text for vicinity definitions.
4. Tornadoes and waterspouts are coded as +FC.
Separate groups are used for each type of present weather. Each group is separated from the other by a space. METAR/SPECI reports contain no more than three present weather groups.
When more than one type of present weather is reported at the same time, present weather is reported in the following order:
Tornadic activity – Tornado, Funnel Cloud, or Waterspout.
Thunderstorm(s) with and without associated precipitation.
Present weather in order of decreasing dominance, i.e., the most dominant type is reported first.
Left-to-right in Table 3-2 (Columns 1 through 5).
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Page 3-10 Section 3: Observed Text Products Qualifiers may be used in various combinations to describe weather phenomena. Present weather qualifiers fall into two categories: intensity (Section 3.1.3.8.1) or proximity (Section
3.1.3.8.2) and descriptors (Section 3.1.3.8.3).
3.1.3.8.1 Intensity Qualifier The intensity qualifiers are light, moderate, and heavy. They are coded with precipitation types except ice crystals (IC) and hail (GR or GS) including those associated with a thunderstorm (TS) and those of a showery nature (SH). Tornadoes and waterspouts are coded as heavy (+FC).
No intensity is ascribed to the obscurations of blowing dust (BLDU), blowing sand (BLSA), and blowing snow (BLSN). Only moderate or heavy intensity is ascribed to sandstorm (SS) and duststorm (DS).
When more than one form of precipitation is occurring at a time or precipitation is occurring with an obscuration, the reported intensities are not cumulative. The reported intensity will not be greater than the intensity for each form of precipitation.
3.1.3.8.2 Proximity Qualifier Weather phenomena occurring beyond the point of observation (between 5 and 10 statute miles) are coded as in the vicinity (VC). VC can be coded in combination with thunderstorm (TS), fog (FG), shower(s) (SH), well-developed dust/sand whirls (PO), blowing dust (BLDU), blowing sand (BLSA), blowing snow (BLSN), sandstorm (SS), and duststorm (DS). Intensity qualifiers are not coded in conjunction with VC.
For example, VCFG can be decoded as meaning some form of fog is between 5 and 10 statute miles of the point of observation. If VCSH is coded, showers are occurring between 5 and 10 statute miles of the point of observation.
Weather phenomena occurring at the point of observation (at the station) or in the vicinity of the point of observation are coded in the body of the report. Weather phenomena observed beyond 10SM from the point of observation (at the station) is not coded in the body but may be coded in the remarks section (Section 3.1.3.12).
3.1.3.8.3 Descriptor Qualifier Descriptors are qualifiers which further amplify weather phenomena and are used in conjunction with some types of precipitation and obscurations. The descriptor qualifiers are: shallow (MI), partial (PR), patches (BC), low drifting (DR), blowing (BL), shower(s) (SH), thunderstorm (TS), and freezing (FZ).
Only one descriptor is coded for each weather phenomena group, e.g., FZDZ.
The descriptors shallow (MI), partial (PR), and patches (BC) are only coded with FG, e.g., MIFG. Mist (BR) is not coded with any descriptor.
The descriptors low drifting (DR) and blowing (BL) will only be coded with dust (DU), sand (SA), and snow (SN), e.g., BLSN or DRSN. DR is coded with DU, SA, or SN for raised particles drifting less than six feet above the ground.
When blowing snow is observed with snow falling from clouds, both phenomena are reported,
e.g., SN BLSN. If blowing snow is occurring and the observer cannot determine whether or not snow is also falling, then BLSN is reported. Spray (PY) is coded only with blowing (BL).