11/14/16 Aviation Weather Services AC 00-45H 3-5 Unlike the IATA codes, the ICAO codes have a regional structure. The first letter identifies the region and country (see Figure 3-2, ICAO Continental Codes). In some regions, the second letter identifies the country. ICAO station identifiers in Alaska begin with PA, Hawaii begins with PH, Guam begins with PG, and Puerto Rico begins with TS. For example, the San Juan Puerto Rico IATA identifier “SJU” becomes the ICAO identifier “TSJU.” The remaining letters are used to identify each airport.
Figure 3-2. ICAO Continental Codes
In the continental United States (CONUS), ICAO station identifiers are coded K, followed by the three-letter IATA identifier. For example, the Seattle, WA IATA identifier SEA becomes the ICAO identifier KSEA.
ICAO station identifiers in Alaska, Hawaii, and Guam begin with the continent code P.
For a list of all U.S. identifiers, refer to the current edition of FAA Order 7350.9, Location Identifiers. For a complete worldwide listing, refer to the current edition of ICAO Document 7910, Location Indicators.
Both are available online.
3.1.5.3 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
11/14/16 Aviation Weather Services AC 00-45H 3-6 The date and time are 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 Coordinated Universal Time (UTC)).
For example, METAR KOKC 011955Z would be disseminated as the 2000 hour routine report for station KOKC, taken on the 1st of the month at 1955 UTC.
3.1.5.4 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.
3.1.5.5 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 90 degrees is coded as 090. A wind from the north is coded as
360.
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 (kts) using the units, tens digits, and, when required, the hundreds digit. When wind speeds are less than 10 kts, a leading 0 is used to maintain at least a two-digit wind code. For example, a wind speed of 8 kts will be coded 08KT. The wind group is
11/14/16 Aviation Weather Services AC 00-45H 3-7 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 kts
• 15014KT Wind 150 degrees at 14 kts
• 340112KT Wind 340 degrees at 112 kts
3.1.5.5.1 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 kts 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 kts with gusts to 35 kts would be coded 27020G35KT.
3.1.5.5.2 Variable Wind Direction (speed 6 kts or less).
Wind direction may be considered variable when, during the previous 2-minute evaluation period, the wind speed was 6 kts or less. In this case, the wind may be coded as VRB in place of the three-digit wind direction. For example, if the wind speed was recorded as 3 kts, it would be coded VRB03KT.
3.1.5.5.3 Variable Wind Direction (speed greater than 6 kts).
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 kts. 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 example, if the wind is variable from 180 degrees to 240 degrees at 10 kts, it would be coded 21010KT 180V240.
3.1.5.5.4 Calm Wind.
When no motion of air is detected, the wind is reported as calm. A calm wind is coded as 00000KT.
3.1.5.6 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
11/14/16 Aviation Weather Services AC 00-45H 3-8 Visibility is a measure of the opacity of the atmosphere. It is defined as the greatest horizontal distance at which selected objects can be seen and identified or its equivalent derived from instrumental measurements.
Prevailing visibility is the reported visibility considered representative of recorded visibility conditions at the manual 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 (sm). 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 1 ½ sm is coded 1 1/2SM. Most other countries use meters (m).
U.S. automated stations use an M to indicate “less than.” For example, M1/4SM means a visibility of less than ¼ sm.
3.1.5.7 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 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 sm or less and/or the RVR for the designated instrument runway is 6,000 feet (ft) or less. Otherwise the RVR group is omitted.
RVR 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 ft would be coded R01L/0800FT. Most other countries use meters.
In the United States, RVR values are coded in increments of 100 ft up to 1,000 ft, increments of 200 ft from 1,000 ft to 3,000 ft, and increments of 500 ft from 3,000 ft to 6,000 ft. Manual RVR is not reported below 600 ft.
For U.S. airports only, the touchdown zone’s (TDZ) RVR is reported. For U.S. airports with multiple runways, the operating runway with the lowest
11/14/16 Aviation Weather Services AC 00-45H 3-9 touchdown RVR is reported. RVR may be reported for up to four designated runways in other countries.
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 ft and 1,000 ft 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 ft 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 ft will be coded R27/P6000FT.
3.1.5.8 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, METAR/SPECI Notations for Reporting Present Weather, are used to code present weather.
11/14/16 Aviation Weather Services AC 00-45H 3-10 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 Heavy PR BC Partial Patches RA SN Rain Snow FG FU Fog Smoke SQ FC Squalls
Funnel Cloud, Tornado or Waterspout4 VC
In the Vicinity3 DR BL Low Drifting Blowing SG IC Snow Grains Ice Crystals (Diamond Dust) VA DU Volcanic Ash Widespread Dust
SS DS Sandstorm
Duststorm SH TS FZ
Shower(s) Thunderstorms Freezing PL GR GS UP Ice Pellets
Hail
Small Hail and/or Snow Pellets Unknown Precipitation
SA HZ PY
Sand
Haze Spray
1. The weather groups are constructed by considering columns 1 through 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.
11/14/16 Aviation Weather Services AC 00-45H 3-11 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 reported first).
• Left-to-right in Table 3-2 (columns 1 through 5).
Qualifiers may be used in various combinations to describe weather phenomena. Present weather qualifiers fall into two categories: intensity (see paragraph 3.1.5.8.1) or proximity (see paragraph 3.1.5.8.2) and descriptors (see paragraph 3.1.5.8.3).
3.1.5.8.1 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. For example, -FZRAPL is light freezing rain and light ice pellets, not light freezing rain and moderate ice pellets.
3.1.5.8.2 Proximity Qualifier.
Weather phenomena occurring beyond the point of observation (between 5 and 10 sm) 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 sm of the point of observation. If VCSH is coded, showers are occurring between 5 and 10 sm 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 10 sm from the point of observation (at the station) is not coded in the body, but may be coded in the remarks section (see paragraph 3.1.5.12).
11/14/16 Aviation Weather Services AC 00-45H 3-12
3.1.5.8.3 Descriptor Qualifier.
Descriptors are qualifiers that 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 fog (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 6 ft 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).
The descriptor for showery-type precipitation (SH) is coded only with one or more of the precipitation qualifiers for rain (RA), snow (SN), ice pellets (PL), small hail (GS), or large hail (GR). When any type of precipitation is coded with VC, the intensity and type of precipitation is not coded.
The descriptor for thunderstorm (TS) may be coded by itself when the thunderstorm is without associated precipitation. A thunderstorm may also be coded with the precipitation types of rain (RA), snow (SN), ice pellets (PL), small hail and/or snow pellets (GS), or hail (GR). For example, a thunderstorm with snow and small hail and/or snow pellets would be coded as TSSNGS. TS is not coded with SH.
The descriptor freezing (FZ) is only coded in combination with fog (FG), drizzle (DZ), or rain (RA) (e.g., FZRA). FZ is not coded with SH.
3.1.5.8.4 Precipitation.
Precipitation is any form of water particle, whether liquid or solid, that falls from the atmosphere and reaches the ground. The precipitation types are:
drizzle (DZ), rain (RA), snow (SN), snow grains (SG), ice crystals (IC), ice pellets (PL), hail (GR), small hail and/or snow pellets (GS), and unknown precipitation (UP). UP is reported if an automated station detects the occurrence of precipitation, but the precipitation sensor cannot recognize the type.
11/14/16 Aviation Weather Services AC 00-45H 3-13 Up to three types of precipitation may be coded in a single present weather group. They are coded in order of decreasing dominance based on intensity.
3.1.5.8.5 Obscuration.
Obscurations are any phenomenon in the atmosphere, other than precipitation, that reduces the horizontal visibility in the atmosphere. The obscuration types are: mist (BR), fog (FG), smoke (FU), volcanic ash (VC), widespread dust (DU), sand (SA), haze (HZ), and spray (PY). Spray (PY) is coded only as BLPY.
With the exception of volcanic ash, low drifting dust, low drifting sand, low drifting snow, shallow fog, partial fog, and patches (of) fog, an obscuration is coded in the body of the report if the surface visibility is less than 7 miles (mi), or considered operationally significant. Volcanic ash is always reported when observed.
3.1.5.8.6 Other Weather Phenomena.
Other weather phenomena types include: well-developed dust/sand whirls (PO), sandstorms (SS), duststorms (DS), squalls (SQ), funnel clouds (FC), and tornados and waterspouts (+FC).
Examples:
-DZ Light drizzle -RASN Light rain and (light) snow SN BR (Moderate) snow, mist -FZRA FG Light freezing rain, fog SHRA (Moderate) rain shower VCBLSA Blowing sand in the vicinity -RASN FG HZ Light rain and (light) snow, fog, haze TS Thunderstorm (without precipitation) +TSRA Thunderstorm, heavy rain +FC TSRAGR BR Tornado, thunderstorm, (moderate) rain, hail, mist
3.1.5.9 Sky Condition 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 Sky condition is a description of the appearance of the sky. It includes either cloud cover, vertical visibility, or clear skies.
11/14/16 Aviation Weather Services AC 00-45H 3-14 The sky condition group is based on the amount of cloud cover (the first three letters) followed by the height of the base of the cloud cover (final three digits). No space is between the amount of cloud cover and the height of the layer. The height of the layer is recorded in feet above ground level (AGL).
Sky condition is coded in ascending order and ends at the first overcast layer.
At mountain stations, if the layer is below station level, the height of the layer will be coded as ///.
Vertical visibility is coded as VV, followed by the vertical visibility into the indefinite ceiling. An indefinite ceiling is a ceiling classification applied when the reported ceiling value represents the vertical visibility upward into surface-based obscuration. No space is between the group identifier and the vertical visibility. Figure 3-3, Obscuration Effects on Slant Range Visibility, illustrates the effect of an obscuration on the vision from a descending aircraft.
Figure 3-3. Obscuration Effects on Slant Range Visibility
The ceiling is 500 ft in both examples, but the indefinite ceiling example (bottom) produces a more adverse impact to landing aircraft. This is because an obscuration (e.g., fog, blowing dust, snow) limits runway acquisition due to reduced slant range visibility. This pilot would be able to see the ground, but not the runway. If the pilot was at approach minimums, the approach could not be continued and a missed approach must be executed.
11/14/16 Aviation Weather Services AC 00-45H 3-15 Clear skies are coded in the format SKC or CLR. When SKC is used, an observer indicates no layers are present; CLR is used by automated stations to indicate no layers are detected at or below 12,000 ft.
Each coded layer is separated from the others by a space. Each layer reported is coded by using the appropriate reportable contraction seen in Table 3-3, METAR/SPECI Contractions for Sky Cover. A report of clear skies (SKC or CLR) is a complete layer report within itself. The abbreviations FEW, SCT, BKN, and OVC will be followed (without a space) by the height of the layer.
Table 3-3. METAR/SPECI Contractions for Sky Cover Reportable Contraction Meaning Summation Amount of Layer VV Vertical Visibility 8/8 SKC or CLR1 Clear 0 FEW2 Few 1/8 – 2/8 SCT Scattered 3/8 – 4/8 BKN Broken 5/8 – 7/8 OVC Overcast 8/8
1. The abbreviation CLR will be used at automated stations when no layers at or below 12,000 ft are reported; the abbreviation SKC will be used at manual stations when no layers are reported.
2. Any layer amount less than 1/8 is reported as FEW.
The height is coded in hundreds of feet above the surface using three digits in accordance with Table 3-4, METAR/SPECI Increments of Reportable Values of Sky Cover Height.
Table 3-4. METAR/SPECI Increments of Reportable Values of Sky Cover Height Range of Height Values (feet) Reportable Increment (feet) Less than or equal to 5,000 To nearest 100 5,001 to 10,000 To nearest 500 Greater than 10,000 To nearest 1,000 The ceiling is the lowest layer aloft reported as broken or overcast. If the sky is totally obscured with ground-based clouds, the vertical visibility is the ceiling.
11/14/16 Aviation Weather Services AC 00-45H 3-16 Figure 3-4. METAR/SPECI Sky Condition Coding
Clouds at 1,200 ft obscure 2/8ths of the sky (FEW). Higher clouds at 3,000 ft obscure an additional 1/8th of the sky, and because the observer cannot see above the 1,200-f t layer, he is to assume that the higher 3,000-ft layer also exists above the lower layer (SCT). The highest clouds at 5,000 ft obscure 2/8ths of the sky, and again since the observer cannot see past the 1,200 and 3,000-f t layers, he is to assume the higher 5,000-ft layer also exists above the lower layers (BKN). The sky condition group would be coded as: FEW012 SCT030 BKN050.
At manual stations, cumulonimbus (CB) or towering cumulus (TCU) is appended to the associated layer. For example, a scattered layer of towering cumulus at 1,500 ft would be coded SCT015TCU, and would be followed by a space if there were additional higher layers to code.
Examples:
SKC No layers are present CLR No layers are detected at or below 12,000 ft AGL FEW004 Few at 400 ft AGL SCT023TCU Scattered layer of towering cumulus at 2,300 ft BKN100 Broken layer (ceiling) at 10,000 ft OVC250 Overcast layer (ceiling) at 25,000 ft VV001 Indefinite ceiling with a vertical visibility of 100 ft FEW012 SCT046 Few clouds at 1,200 ft, scattered layer at 4,600 ft