Chapter 24, Observations 24-24
24.4.3.13.19.3 Standing Lenticular or Rotor Clouds
Stratocumulus ( SCSL), altocumulus ( ACSL), 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.
24.4.3.13.20 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 ft, the
remark would be coded CIG 002 RWY11.
24.4.3.13.21 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 in ch 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 pressure rising rapidly (PRESRR) or pressure
falling rapidly (PRESFR) is included in the remarks.
24.4.3.13.22 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 millibars. The hundreds and thousands units are not coded
and must be inferred. For example, a sea level pressure of 998.2 mb is coded SLP982. A sea level pressure
of 1,013.2 mb would be coded SLP132. For a METAR, if sea level pressure is not available, it is coded
SLPNO.
24.4.3.13.23 Aircraft Mishap
If a SPECI is taken to document weather conditions when notified of an aircraft mishap, the remark
ACFT MSHP is coded in the report, but the SPECI is not transmitted.
24.4.3.13.24 No SPECI Reports Taken
At manual stations where SPECIs are not taken, the remark NOSPECI is coded to indicate that no changes
in weather conditions will be reported until the next METAR.
24.4.3.13.25 Snow Increasing Rapidly
At designated stations, the snow increasing rapidly remark is reported in the next METAR whenever the
snow depth increases by one 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 increased 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 in ch in the past hour
with a total depth on the ground of 10 inch is coded SNINCR 2/10.
24.4.3.13.26 Other Significant Information
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.
Chapter 24, Observations 24-25
24.4.3.14 Additive and Automated Maintenance Data
Additive data groups (see Table 24-6) 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.
24.4.3.14.1 Hourly Temperature and Dewpoint
At designated stations, the hourly temperature and dewpoint group are further coded to the tenth of a degree
Celsius. For example, a recorded temperature of +2.6 °C and dewpoint of -1.5°C would be coded
T00261015.
The format for the coding is as follows:
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 tenth 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 Dewpoint disseminated to the nearest tenth and read as 01.5.
No spaces are between the entries. For example, a temperature of 2.6°C and dewpoint of -1.5°C is reported
in the body of the report as 03/M01 and the hourly temperature and dewpoint group as T00261015. If the
dewpoint is missing, only the temperature is reported; if the temperature is missing, the hourly temperature
and dewpoint group are not reported.
24.4.3.14.2 Maintenance Data Groups
The following maintenance data groups, sensor status indicators and the maintenance indicator, are only
reported from automated stations.
24.4.3.14.2.1 Sensor Status Indicators
Sensor status indicators are reported as indicated below:
• If the RVR 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.
Chapter 24, Observations 24-26
24.4.3.14.2.2 Maintenance Indicator
A maintenance indicator ($) is coded when an automated system detects that maintenance is needed on the
system.
24.5 Aircraft Observations and Reports
There are three kinds of aircraft observations: Pilot Weather Reports (PIREP), Aircraft Reports (AIREP),
and Volcanic Activity Reports (VAR). Both PIREPs and AIREPS have two types:
• Routine PIREPs and Urgent PIREPs.
• Routine AIREPs and Special AIREPs.
PIREPs are reported by the pilot (or aircrew), while AIREPs can either be reported by the pilot or generated
from sensors onboard the aircraft (automated AIREPs). PIREPs and AIREPs are coded differently. The
PIREP format is a U .S.-only format. The AIREP format is used worldwide. Automated AIREPs are
common over the United States.
The VAR is a report for aircraft encounters with volcanic ash and/or sulfur dioxide (SO2).
24.5.1 Pilot Weather Reports (PIREP)
Pilots can 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 can also report the observed condition. This
will help the NWS verify forecast products and create more accurate products for the aviation community.
A PIREP is prepared using a prescribed format (see Figure 24-5). Elements for all PIREPs are message
type, location, time, altitude/ FL, type aircraft, and at least one other element to describe the reported
phenomena. The other elements are omitted when no data is reported. All altitude references are mean sea
level unless otherwise noted. Distance for visibility is in statute miles and all other distances are in nautical
miles. Time is reported in Coordinated Universal Time.
Figure 24-5. PIREP Coding Format
Chapter 24, Observations 24-27
24.5.1.1 Message Type (UUA/UA)
The two types of PIREPs are Urgent (UUA) and Routine (UA).
24.5.1.1.1 Urgent PIREPs
Urgent (UUA) PIREPs contain information about:
• Tornadoes, funnel clouds, and waterspouts;
• Severe or extreme turbulence (including CAT);
• Severe icing;
• Hail;
• LLWS within 2,000 ft of the surface (LLWS PIREPs are classified as UUA if the pilot reports air
speed fluctuations of 10 kt or more ; or, if air speed fluctuations are not reported but LLWS is
reported, the PIREP is classified as UUA);
• Volcanic ash clouds;
• Any other weather phenomena reported that are considered by the air traffic controller or Flight
Service specialist receiving the report as being hazardous, or potentially hazardous, to flight
operations.
24.5.1.1.2 Routine PIREPs
Routine (UA) PIREPs are issued after receiving a report from a pilot that does not contain any urgent
information as listed in Section 24.5.1.1.1.
24.5.1.2 Location (/OV)
The location (/OV) is the position reference where the phenomenon occurred. It is not the location of the
aircraft when the report is submitted . Location can be referenced either by geographical position or by
route segment. A position reference is preferred by meteorologists to aid forecast precision, monitoring,
and verification.
24.5.1.2.1 Geographical Position
Geographical position can be referenced to a VHF Navigational Aid (NAVAID) or an airport, using either
the three -letter IATA or four -letter ICAO identifier. If appropriate, the PIREP is encoded using the
identifier, then three digits to define a radial, and three digits to define the distance in nautical miles.
Examples:
/OV APE Over the Appleton VHF omni-directional range station (VOR).
/OV KJFK Over John F. Kennedy International Airport, New York, NY.
/OV APE230010 230° at 10 NM from the Appleton VOR.
/OV KJFK107080 107° at 80 NM from John F. Kennedy International Airport, New York, NY.
Chapter 24, Observations 24-28
24.5.1.2.2 Route Segment
A PIREP can also be referenced using two or more fixes to describe a route.
Examples:
/OV KSTL-KMKC From St. Louis Lambert International Airport, St. Louis, MO, to
Charles B. Wheeler Downtown Airport, Kansas City, MO.
/OV KSTL090030-KMKC045015 From 90° at 30 NM from St. Louis Lambert International Airport,
St. Louis, MO, to 45 ° at 15 NM from Charl es B. Wheeler
Downtown Airport, Kansas City, MO.
24.5.1.3 Time (/TM)
Time (/TM) is the time when the reported phenomenon occurred or was encountered. It is coded in four
digits UTC.
Example:
/TM 1315 1315 UTC.
24.5.1.4 Altitude/Flight Level (/FL)
The altitude/flight level ( /FL) is the altitude in hundreds of feet MSL where the phenomenon was first
encountered. If not known, UNKN is entered. If the aircraft was climbing or descending, the appropriate
contraction (DURC or DURD) is entered in the remarks (/RM). If the condition was encountered within a
layer, the altitude range is entered within the appropriate element that describes the condition.
Examples:
/FL085 8,500 ft MSL.
/FL310 Flight level 310.
/FLUNKN /RM DURC Flight level unknown, remarks, during climb.
24.5.1.5 Aircraft Type (/TP)
Aircraft type (/TP) is entered. If not known, UNKN is entered. Icing and turbulence reports always include
aircraft type.
Examples:
/TP BE20 Super King Air 200.
/TP SR22 Cirrus 22.
/TP P28R Piper Arrow.
/TP UNKN Type unknown.
24.5.1.6 Sky Condition (/SK)
The sky condition (/SK) group is used to report height of cloud bases, tops, and cloud cover. The height of
base of a layer of clouds is coded in hundreds of feet MSL. The top of a layer is entered in hundreds of feet
MSL preceded by the word TOP. If reported as clear above the highest cloud layer, SKC is coded following
the reported level.
Chapter 24, Observations 24-29
Examples:
/BKN040-TOP065 Base of broken layer 4,000 ft MSL, top 6,500 ft MSL.
/SK OVC100-TOP110/ SKC Base of an overcast layer 10,000 ft MSL, top 11,000 ft MSL,
clear above.
/SK OVC015-TOP035/OVC230 Base of an overcast layer 1,500 ft MSL, top 3,500 ft MSL, base
of an overcast layer 23,000 ft MSL.
/SK OVC-TOP085 Overcast layer, top 8,500 ft MSL.
Cloud cover amount ranges are entered with a hyphen separating the amounts (e.g., BKN-OVC).
Examples:
/SK SCT-BKN050-TOP100 Base of a scattered to broken layer
5,000 ft MSL, top 10,000 ft MSL.
/SK BKN-OVCUNKN-TOP060/BKN120-TOP150/ SKC Base of a broken to overcast layer
unknown, top 6,000 ft MSL , base of a
broken layer 12,000 ft MSL, top
15,000 ft MSL, clear above.
Unknown heights are indicated by the contraction UNKN.
Examples:
/SK OVC065-TOPUNKN Base of an overcast layer 6,500 ft MSL, top unknown. If a
pilot indicates being in the clouds, IMC is entered.
/SK OVC065-TOPUNKN /RM IMC Base of an overcast layer 6,500 ft MSL, top unknown,
remark, in the clouds. When more than one layer is reported,
layers are separated by a solidus (/).
24.5.1.7 Flight Visibility and Weather (/WX)
The pilot reports the weather conditions encountered as follows: flight visibility, when reported, is entered
first in the /WX field. It is coded FV followed by a two-digit visibility value rounded down, if necessary,
to the nearest whole statute mile and appended with SM (e.g., FV03SM). If visibility is reported as
unrestricted, FV99SM is entered.
Flight weather types are entered using one or more of the surface weather reporting phenomena contained
in Table 24-3.
Example:
/WX FV01SM +DS000-TOP083/SKC /RM DURC Flight visibility 1 SM, base heavy dust storm
layer at the surface, top 8,300 ft MSL, clear
above, remarks, during climb.
When more than one form of precipitation is combined in the report, the dominant type is reported first.
Examples:
/WX FV00SM +TSRAGR Flight visibility 0 SM, thunderstorm, heavy rain, hail.
/WX FV02SM BRHZ000-TOP083 Flight visibility 2 SM, base of a haze and mist layer at the
surface, top 8,300 ft MSL.
Chapter 24, Observations 24-30
If a funnel cloud is reported, it is coded FC following the /WX group and is spelled out as FUNNEL
CLOUD after the /RM group. If a tornado or waterspout is reported, it is coded +FC following the /WX
group, and TORNADO or WATERSPOUT is spelled out after the /RM group. If a dust/sand whirl
(dust devil) is reported, it is coded FC following the /WX group, and DUST/SAND WHIRL (DUST
DEVIL) is spelled out after the /RM group.
Examples:
/WX FC /RM FUNNEL CLOUD Funnel cloud, remarks, funnel cloud.
/WX +FC /RM TORNADO Tornado, remarks, tornado.
When more than one type of weather is reported, they are reported in the following order:
• TORNADO, WATERSPOUT, FUNNEL CLOUD, or DUST/SAND WHIRL (DUST DEVIL).
• Thunderstorm with or without associated precipitation.
• Weather phenomena in order of decreasing predominance.
• No more than three groups are used in a single PIREP.
• Weather layers are entered with the base and/or top of the layer when reported. The same format
as in the sky condition (/SK) group is used.
Example:
/WX FU002-TOP030 Base of a smoke layer, 200 ft MSL, top 3,000 ft MSL.
24.5.1.8 Air Temperature (/TA)
Outside air temperature ( /TA) is reported using two digits in degrees Celsius. Negative temperatures are
prefixed with an M (e.g., /TA 08 or /TA M08).
24.5.1.9 Wind Direction and Speed (/WV)
Wind direction and speed are encoded using three digits to indicate wind direction, relative to magnetic
north, and two or three digits to indicate reported wind speed. When the reported speed is less than 10 kt, a
leading 0 is used. The wind group will always have KT appended to represent the units in knots.
Examples:
/WV 02009KT Wind 20° at 9 kt.
/WV 28057KT Wind 280° at 57 kt.
/WV 350102KT Wind 350° at 102 kt.
24.5.1.10 Turbulence (/TB)
Turbulence intensity, type, and altitude are reported after wind direction and speed.
Duration (intermittent ( INTMT), occasional ( OCNL), or continuous ( CONS)) is coded first (if reported
by the pilot), followed by the intensity (light ( LGT), moderate ( MOD), severe ( SEV), or extreme
(EXTRM)). Range or variation of intensity is separated with a hyphen (e.g., MOD-SEV). If turbulence
was forecasted but not encountered, negative (NEG) is entered.
Type is coded second. CAT or CHOP is entered if reported by the pilot. High -level turbulence , not
associated with clouds (including thunderstorms), is reported as CAT.