Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 3-5. Cumulonimbus (CB) Example CB always evolves from the further development of towering cumulus (TCU). The usual occurrence of lightning and thunder within or from a CB leads to its popular title, thunderstorm. A thunderstorm usually contains severe or greater turbulence, severe icing, low level wind shear (LLWS), and instrument flight rules (IFR) conditions. (Copyright Robert A. Prentice, 1990)
Figure 3-6. Cumulonimbus Mammatus (CBMAM) Example Cumulonimbus Mammatus (CBMAM) (also called mammatus) appears as hanging protuberances, like pouches, on the undersurface of a cloud. (Copyright Robert A. Prentice, 1993) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-21
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.13.19.2 Towering Cumulus Towering cumulus clouds are coded in the following format: the identifier TCU followed by the direction from the station. The cloud type and direction entries are separated by a space. For example, a towering cumulus cloud up to 10 statute miles west of the station is coded as TCU W.
Figure 3-7. Towering Cumulus (TCU) Example Towering Cumulus (TCU). TCU is produced by strong convective updrafts and, thus, indicates turbulence.
Icing is typically found above the freezing level. TCU often transforms into cumulonimbus (CB). (Copyright Charles A. Doswell, III, 1977)
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.13.19.3 Altocumulus Castellanus Altocumulus Castellanus is coded in the following format: the identifier ACC followed by direction from the station. The cloud type and direction entries are separated by a space. For example, an altocumulus cloud 5 to 10 statute miles northwest of the station is coded ACC NW.
Figure 3-8. Altocumulus Castellanus (ACC) Example Altocumulus Castellanus (ACC). ACC indicates convective turbulence aloft from the top of the cloud to its base and usually an undetermined height below cloud base as well. (Photo courtesy of National Severe Storms Laboratory/University of Oklahoma)
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.13.19.4 Standing Lenticular or Rotor Clouds Stratocumulus (SCSL), altocumulus (ACSL), or cirrocumulus (CCSL), or rotor clouds are coded in the following format: the cloud type followed by the direction from the station. The cloud type and direction entries are separated by a space. For example, altocumulus standing lenticular clouds observed southwest through west of the station are coded ACSL SW-W; an apparent rotor cloud 5 to 10 statute miles northeast of the station is coded APRNT ROTOR CLD NE; and cirrocumulus clouds south of the station are coded CCSL S.
Figure 3-9. Standing Lenticular and Rotor Clouds Example From top to bottom: Cirrocumulus standing lenticular (CCSL), altocumulus standing lenticular (ACSL), and rotor cloud. These clouds are characteristic of mountain waves. Mountain waves can occasionally produce violent downslope windstorms. Intense mountain waves can present a significant hazard to aviation by producing severe or even extreme turbulence that extends upward into the lower stratosphere.
3.1.3.13.20 Ceiling Height at Second Location At designated stations, the ceiling height at a second location is coded in the following format:
the identifier CIG followed by the measured height of the ceiling and the specific location of the ceilometer(s) at the station. This remark is only generated when the ceiling is lower than that contained in the body of the report. For example, if the ceiling measured by a second sensor located at runway 11 is broken at 200 feet, the remark would be CIG 002 RWY11.
AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-24
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.3.13.21 Pressure Rising or Falling Rapidly At designated stations, the reported pressure is evaluated to determine if a pressure change is occurring. If the pressure is rising or falling at a rate of at least 0.06 inch per hour and the pressure change totals 0.02 inch or more at the time of the observation, a pressure change remark is reported. When the pressure is rising or falling rapidly at the time of observation, the remark PRESRR (pressure rising rapidly) or PRESFR (pressure falling rapidly) is included in the remarks.
3.1.3.13.22 Sea-Level Pressure At designated stations, the sea-level pressure is coded in the following format: the identifier SLP immediately followed by the sea level pressure in hectopascals. The hundreds and thousands units are not coded and must be inferred. For example, a sea-level pressure of
998.2 hectopascals is coded as SLP982. A sea-level pressure of 1013.2 hectopascals would be coded as SLP132. For a METAR, if sea-level pressure is not available, it is coded as SLPNO.
3.1.3.13.23 Aircraft Mishap (Plain Language) If a SPECI report is taken to document weather conditions when notified of an aircraft mishap, the remark ACFT MSHP is coded in the report but the SPECI not transmitted.
3.1.3.13.24 No SPECI Reports Taken (Plain Language) At manual stations where SPECIs are not taken, the remark NOSPECI is coded to indicate no changes in weather conditions will be reported until the next METAR.
3.1.3.13.25 Snow Increasing Rapidly At designated stations, the snow increasing rapidly remark is reported, in the NEXT METAR, whenever the snow depth increases by 1 inch or more in the past hour. The remark is coded in the following format: the remark indicator SNINCR, the depth increase in the past hour, and the total depth of snow on the ground at the time of the report. The depth of snow increase in the past hour and the total depth on the ground are separated from each other by a solidus, /. For example, a snow depth increase of 2 inches in the past hour with a total depth on the ground of 10 inches is coded SNINCR 2/10.
3.1.3.13.26 Other Significant Information (Plain Language) Agencies may add to a report other information significant to their operations, such as information on fog dispersal operations, runway conditions, FIRST or LAST reports from station, etc.
3.1.3.14 Additive and Automated Maintenance Data Additive data groups (Table 3-5) are only reported at designated stations and are primarily used by the NWS for climatological purposes. Most have no direct impact on the aviation community but a few are discussed below.
3.1.3.14.1 Hourly Temperature and Dew Point At designated stations, the hourly temperature and dew point group are further coded to the tenth of a degree Celsius. For example, a recorded temperature of +2.6ºC and dew point of -1.5ºC would be coded as T00261015.
The format for the coding is as follows:
AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-25
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) T Group indicator 0 Indicates the following number is positive; a 1 would be used if the temperature was reported as negative at the time of observation 026 Temperature disseminated to the nearest 10 th and read as 02.6 1 Indicates the following number is negative; a 0 would be used if the number was reported as positive at the time of observation 015 Dew Point disseminated to the nearest 10th and read as 01.5
No spaces are between the entries. For example, a temperature of 2.6ºC and dew point of –
1.5ºC is reported in the body of the report as 03/M01 and the hourly temperature and dew point group as T00261015. If the dew point is missing only the temperature is reported; if the temperature is missing the hourly temperature and dew point group is not reported.
3.1.3.14.2 Maintenance Data Groups The following maintenance data groups, Sensor Status Indicators and the Maintenance Indicator, are only reported from automated stations.
3.1.3.14.2.1 Sensor Status Indicators Sensor status indicators are reported as indicated below:
• If the Runway Visual Range is missing and would normally be reported, RVRNO is coded
• When automated stations are equipped with a present weather identifier and the sensor is not operating, the remark PWINO is coded
• When automated stations are equipped with a tipping bucket rain gauge and the sensor is not operating, PNO is coded
• When automated stations are equipped with a freezing rain sensor and the sensor is not operating, the remark FZRANO is coded
• When automated stations are equipped with a lightning detection system and the sensor is not operating, the remark TSNO is coded
• When automated stations are equipped with a secondary visibility sensor and the sensor is not operating, the remark VISNO LOC is coded
• When automated stations are equipped with a secondary ceiling height indicator and the sensor is not operating, the remark CHINO LOC is coded
3.1.3.14.2.2 Maintenance Indicator A maintenance indicator, $, is coded when an automated system detects maintenance is needed on the system.
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.1.4 METAR/SPECI Examples
METAR PAHL 031836Z AUTO 07009KT 10SM CLR 13/02 A2980 RMK AO1 PNO
GROUP CODED TRANSLATION Type of Report METAR Aviation Routine Weather Report Station Identifier PAHL United States Huslia, Alaska Date and Time of Report 031836Z 3rd day of the month, 1836 UTC Report Modifier AUTO automated observation with no human augmentation Wind 07009KT Wind from 070 degrees (the east) at 9 knots (10 mph, 4.6 m/s) Visibility 10SM Visibility ten statute miles (16 kilometers) Runway Visual Range [omitted] Present Weather [omitted] There may or may not be significant weather present at this time Sky Condition CLR Sky clear below 12,000 feet AGL Temperature/Dewpoint 13/02 Temperature 13°C (55°F), dewpoint 2°C (36°F) Altimeter A2980 29.80 inches of mercury (1009.2 millibars, 1009.2 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language A01 Automated station without a precipitation discriminator Additive and Automated Maintenance Data PNO Tipping bucket rain gauge not operating
METAR KNSI 031656Z VRB03KT 5SM HZ SCT007 21/17 A2989 RMK SLP121 T02060172
GROUP CODED TRANSLATION Type of Report METAR Aviation Routine Weather Report Station Identifier KNSI United States San Nicolas Island, California Date and Time of Report 031656Z 3rd day of the month, 1656 UTC Report Modifier [omitted] Either a manual or an augmented observation Wind VRB03KT Wind variable at 3 knots (4 mph, 1.5 m/s) Visibility 5SM Visibility five statute miles (8.0 kilometers) Runway Visual Range [omitted] Present Weather HZ Haze Sky Condition SCT007 Scattered at 700 feet AGL Temperature/Dewpoint 21/17 Temperature 21°C (69°F), dewpoint 17°C (63°F) Altimeter A2989 29.89 inches of mercury (1012.3 millibars, 1012.3 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language SLP121 Sea level pressure 1012.1 hectopascals (1012.1 millibars) Additive and Automated Maintenance Data T02060172 Temperature 20.6°C (69°F), dewpoint 17.2°C (63°F) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-27
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
SPECI KCOT 292020Z AUTO 13009KT 3SM TSRA BR SCT011 BKN028 OVC043 23/21 A2991 RMK AO2 PK WND 13029/2000 LTG DSNT ALQDS P0020
GROUP CODED TRANSLATION Type of Report SPECI Aviation Selected Special Weather Report Station Identifier KCOT United States Cotulla, Texas Date and Time of Report 292020Z 29th day of the month, 2020 UTC Report Modifier AUTO Automated observation with no human augmentation Wind 13009KT Wind from 130 degrees (the southeast) at 9 knots (10 mph, 4.7 m/s) Visibility 3SM Visibility three statute miles (5 kilometers) Runway Visual Range [omitted] Present Weather TSRA BR Thunderstorm, moderate rain, mist Sky Condition SCT011 BKN028 OVC043 Scattered at 11,000 feet AGL, Ceiling broken at 2,800 feet AGL, Overcast at 4,300 feet AGL Temperature/Dewpoint 23/21 Temperature 23°C (73°F), dewpoint 21°C (70°F) Altimeter A2991 29.91 inches of mercury (1013.0 millibars, 1013.0 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language AO2 Automated station with a precipitation discriminator PK WND 13029/2000 Peak wind from 130 degrees (the southeast) at 29 knots (33 mph, 14.9 m/s) occurred at 2000 UTC
LTG DSNT ALQDS Lightning distant all quadrants Additive and Automated Maintenance Data P0020 0.20 inches of precipitation fell in the past hour
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
METAR KMDW 090153Z 23003KT 1/2SM R31C/4000V4500FT SN FZFG VV002 M04/M05 A3004 RMK AO2 SLP191 SNINCR 1/10 P0000 T10391050
GROUP CODED TRANSLATION Type of Report METAR Aviation Routine Weather Report Station Identifier KCOT United States Chicago (Midway), Illinois Date and Time of Report 090153Z 9th day of the month,0153 UTC Report Modifier [omitted] Either a manual or an augmented observation Wind 23003KT Wind from 230 degrees (the southwest) at 3 knots (3 mph,1.6 m/s) Visibility 1/2SM Visibility one-half statute miles (0.8 kilometers) Runway Visual Range R31C/4000V4500FT Runway 31 center visual range variable between 4,000 and 4,5000 feet Present Weather SN FZFG Snow, freezing fog Sky Condition VV002 Indefinite ceiling, vertical visibility 200 feet Temperature/Dewpoint M04/M05 Temperature -4°C (25°F), dewpoint -5°C (23°F) Altimeter A3004 Altimeter 30.04 inches of mercury (1017.4 hectopascals, 1017.4 millibars) Remarks RMK Remarks section designator Automated, Manual, and Plain Language A02 Automated station with a precipitation discriminator SLP191 Sea level pressure 1019.1 hectopascals (1019.1 millibars) SNINCR 1/10 Snow increasing rapidly, snow depth increase of 1 inch in the past hour, a total depth on the ground of 10 inches Additive and Automated Maintenance Data P0000 Less than 1/100 of an inch of precipitation fell in the past hour T10391050 Temperature -3.9°C (25°F), dewpoint -
5.0°C (23°F)
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
SPECI KMEM 091826 27013G27KT 240V310 1/2SM R36L/1000VP6000FT +TSRAGR FG FEW002 BKN023 OVC032CB 18/17 A2992 RMK A02 PK WND 31031/1802 WSHFT 1759 TSB22RAB17GRB23 PRESRR FRQ LTGIC W-NW TS W-NW GR 1/2 P0005
GROUP CODED TRANSLATION Type of Report SPECI Aviation Selected Special Weather Report Station Identifier KMEM United States Memphis, Tennessee Date and Time of Report 091826Z 9th day of the month, 1826 UTC Report Modifier [omitted] Either a manual or an augmented observation Wind 27013G27KT 240V310 Wind from 270 degrees (the west) at 13 knots (15 mph, 6.7 m/s) gusting to 27 knots (31 mph, 13.9 m/s), wind variable between 240 degrees (the westsouthwest) and 310 degrees (the northwest) Visibility 1/2SM Visibility one-half statute miles (0.8 kilometers) Runway Visual Range R36L/1000VP6000FT Runway 36 left visual range variable between 1,000 and more than 6,000 feet Present Weather +TSRAGR FG Thunderstorm, heavy rain, hail, fog Sky Condition FEW002 BKN023 OVC032CB Few at 200 feet AGL, ceiling broken at 2,300 feet AGL, overcast at 3,200 feet AGL cumulonimbus Temperature/Dewpoint 18/17 Temperature 18°C (64°F), dewpoint 17°C (63°F) Altimeter A2992 29.92 inches of mercury (1013.2 millibars, 1013.2 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language AO2 Automated station with a precipitation discriminator PK WND 31031/1802 Peak wind from 310 degrees (the northwest) at 31 knots (36 mph, 15.9 m/s) occurred at 1802 or 2 minutes past the hour UTC WSHFT 1759 Wind shift occurred at 1759 UTC TSB22RAB17GRB23 Thunderstorm began at 22 minutes past the hour, rain began at 17 minutes past the hour, hail began at 23 minutes past the hour PRESRR Pressure rising rapidly FRQ LTGIC W-NW Frequent lightning in-cloud west through northwest TS W-NW Thunderstorm west through northwest GR1/2 Largest hailstone 1/2 inches in diameter Additive and Automated Maintenance Data P0005 0.05 inches of precipitation fell in the past hour AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-30
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
SPECI KMSN 012312Z 13021G26KT 1SM -FZRAPL BR OVC011 00/M02 A2988 RMK AO2 PK WND 14031/2255 SFC VIS 1 1/2 P0005 $
GROUP CODED TRANSLATION Type of Report SPECI Aviation Selected Special Weather Report Station Identifier KMSN United States Madison, Wisconsin Date and Time of Report 012312Z 1st day of the month, 2312 UTC Report Modifier [omitted] Either a manual or an augmented observation Wind 13021G26KT Wind from 130 degrees (the southeast) at 21 knots (24 mph, 10.8 m/s) gusting to 26 knots (30 mph, 13.4 m/s) Visibility 1SM Visibility one statute mile (1.6 kilometers) Runway Visual Range [omitted] Present Weather -FZRAPL BR Light freezing rain, ice pellets, mist Sky Condition OVC011 Ceiling overcast at 1,100 feet AGL Temperature/Dewpoint 00/M02 Temperature 0°C (32°F), dewpoint -2°C (28°F) Altimeter A2988 29.88 inches of mercury (1011.9 millibars, 1011.9 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language AO2 Automated station with a precipitation discriminator PK WND 14031/2255 Peak wind from 140 degrees (the southeast) at 31 knots (36 mph, 15.9 m/s) occurred at 2255 UTC SFC VIS 1 1/2 Surface visibility one and on-half statute mile Additive and Automated Maintenance Data P0005 0.05 inches of precipitation fell in the past hour $ Maintenance is needed on the system
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Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
3.2 Pilot Weather Reports (PIREP) No report is timelier than the one made from the flight deck of aircraft in flight. In fact, aircraft in flight are the only means of observing actual icing and turbulence conditions. Pilots welcome pilot weather reports (PIREPs) as well as pilot weather briefers and forecasters. Pilots should report any observation, good or bad, to assist other pilots with flight planning and preparation. If conditions were forecasted to occur but not encountered, a pilot should also report this inaccuracy. This will help the NWS verify forecast products and create more accurate products for the aviation community. Pilots should help themselves, the aviation public, and the aviation weather forecasters by providing PIREPs.
Pipe Up with a PIREP and help the aviation community operate more safely and effectively.
PIREPs are available in the internet at the Aviation Digital Data Service (ADDS) web page at:
http://adds.aviationweather.gov/pireps/
3.2.1 Format A PIREP is transmitted in a prescribed format (Figure 3-7). Required elements for all PIREPs are: message type, location, time, altitude/flight level, type aircraft, and at least one other element to describe the reported phenomena. The other elements will be omitted when no data is reported with them. All altitude references are mean sea level (MSL) unless otherwise noted.
Distance for visibility is in statute miles and all other distances are in nautical miles. Time is reported in Universal Time Coordinated (UTC).
Figure 3-10. Pilot Weather Report (PIREP) Coding Format
3.2.1.1 Message Type (UUA/UA) The two types of PIREPs are Urgent (UUA) and Routine (UA).
3.2.1.1.1 Urgent PIREPs Urgent (UUA) PIREPs contain information about:
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