Chapter 24, Observations 24-31
Altitude is reported last and only if it differs from the value reported in the altitude/flight level (/FL) group.
When a layer of turbulence is reported, height values are separated with a hyphen. If lower or upper limits
are not defined, below (BLO) or above (ABV) is used.
Examples:
/TB LGT Light turbulence.
/TB LGT 040 Light turbulence at 4,000 ft MSL.
/TB OCNL MOD-SEV BLO 080 Occasional moderate to severe turbulence below
8,000 ft MSL.
/TB MOD-SEV CAT 350 Moderate to severe CAT at 35,000 ft MSL.
/TB NEG 120-180 Negative turbulence between 12,000 and
18,000 ft MSL.
/TB CONS MOD CHOP 220/NEG 230-280 Continuous moderate chop at 22,000 ft MSL,
negative turbulence between 23,000 and
28,000 ft MSL.
/TB MOD CAT ABV 290 Moderate CAT above 29,000 ft MSL.
Turbulence reports should include location, altitude (or range of altitudes), and aircraft type, as well as,
when reported, whether in clouds or clear air. The pilot determines the degree of turbulence, intensity, and
duration (occasional, intermittent, or continuous). Reports should be obtained and disseminated, when
possible, in conformance with the Turbulence Reporting Criteria Table in the AIM, Chapter 7, Section 1 ,
Meteorology.
24.5.1.11 Icing (/IC)
Icing intensity, type, and altitude are reported after turbulence.
Intensity is coded first using contractions TRACE, light ( LGT), moderate (MOD), or severe ( SEV).
Reports of a range or variation of intensity is separated with a hyphen. If icing was forecast but not
encountered, negative ( NEG) is coded. Icing type is reported second. Reportable types are RIME, clear
(CLR), or mixed (MX).
The AIM, Chapter 7, Section 1, Meteorology provides classification of icing intensity, according to its
operational effects on aircraft, as well as tables of icing types and icing conditions.
The reported icing/altitude is coded last , and only if different from the value reported in the altitude/flight
level (/FL) group. A hyphen is used to separate reported layers of icing. Above ( ABV) or below (BLO) is
coded when a layer is not defined.
Pilot reports of icing should also include air temperature (/TA).
Examples:
/IC LGT-MOD MX 085 Light to moderate mixed icing, 8,500 ft MSL.
/IC LGT RIME Light rime icing.
/IC MOD RIME BLO 095 Moderate rime icing below 9,500 ft MSL.
/IC SEV CLR 035-062 Severe clear icing 3,500 to 6,200 ft MSL.
Chapter 24, Observations 24-32
24.5.1.12 Remarks (/RM)
The remarks (/RM) group is used to report a phenomenon that is considered important but does not fit in
any of the other groups. This includes, but is not limited to, LLWS reports, thunderstorm lines, coverage
and movement, lightning, SO 2 gas smell, clouds observed but not encountered, and geographical or local
descriptions of where the phenomenon occurred. Hazardous weather is reported first. LLWS is described
to the extent possible.
24.5.1.12.1 Wind Shear
Fluctuations in wind speed 10 kt or more (±10 kt), within 2,000 ft of the surface, are issued as an Urgent
(UUA) PIREP. When LLWS is entered in a PIREP, LLWS is entered as the first remark in the remarks
(/RM) group.
Example:
/RM LLWS +/-15 KT SFC-008 DURC RY22 JFK Remarks, LLWS, air speed fluctuations
of plus or minus 15 kt, surface to 800 ft
during climb, Runway 22, John F.
Kennedy International Airport, New
York, NY.
24.5.1.12.2 Funnel Cloud, Tornado, Waterspout, and Dust/Sand Whirls
FUNNEL CLOUD, TORNADO, WATERSPOUT, and DUST/SAND WHIRLS are entered with the
direction of movement, when reported.
Example:
/RM TORNADO W MOV E Remarks, tornado west moving east.
24.5.1.12.3 Thunderstorm
Thunderstorm coverage is coded as isolated (ISOL), few (FEW), scattered (SCT), or numerous (NMRS),
followed by a description as line ( LN), broken line ( BKN LN), or solid line ( SLD LN), when reported.
This is followed with TS, the location and movement, and the type of lightning, when reported.
Example:
/RM NMRS TS S MOV E Remarks, numerous thunderstorms south moving east.
24.5.1.12.4 Lightning
Lightning frequency is coded as occasional ( OCNL) or frequent (FRQ), followed by type as lightning in
cloud (LTGIC), lightning cloud to cloud (LTGCC), lightning cloud to ground (LTGCG), lightning cloud
to air (LTGCA), or combinations, when reported.
Example:
/RM OCNL LTGICCG Remarks, occasional lighting in cloud, cloud to ground.
24.5.1.12.5 Electrical Discharge
For an electrical discharge, DISCHARGE is coded followed by the altitude.
Example:
/RM DISCHARGE 120 Remarks, discharge, 12,000 ft MSL.
Chapter 24, Observations 24-33
24.5.1.12.6 Clouds
Remarks are used when clouds can be seen but were not encountered and reported in the sky condition
group (/SK).
Examples:
/RM CB E MOV N Remarks, cumulonimbus east moving north.
/RM OVC BLO Remarks, overcast below.
24.5.1.12.7 Other Remarks
Remarks that do not fit in other groups, like during climb (DURC), during descent (DURD), reach cruising
altitude (RCA), or top of climb (TOP or TOC), may be included. If specific phraseology or contractions
are not adequate, plain language is used to describe the phenomena or local geographic locations.
Example:
/RM DONNER SUMMIT PASS
24.5.1.12.8 Volcanic Eruptions
Volcanic ash alone is an Urgent PIREP. A report of volcanic activity includes as much information as
possible, including the name of the mountain, ash cloud and movement, height of the top and bottom of the
ash, etc.
Example:
/UUA/OV ANC240075/TM 2110/FL370/TP DC10/WX VA/RM VOLCANIC ERUPTION 2008Z MT
AUGUSTINE ASH 40S MOV SSE
Urgent PIREP, 240° at 75 NM from Anchorage International Airport, Anchorage, AK, 2110 UTC, FL370,
a DC-10 reported volcanic ash, remarks, volcanic eruption occurred at 2 008 UTC Mount Augustine, ash
40 NM south moving south-southeast.
24.5.1.12.9 SkySpotter
The SKYSPOTTER program is a result of a recommendation from the “Safer Skies” FAA/Industry Joint
Safety Analysis and Implementation Teams. The term SKYSPOTTER indicates a pilot has received
specialized training in observing and reporting in-flight weather phenomena or PIREPs.
When a PIREP is received from a pilot identifying themselves as a SKYSPOTTER aircraft, the additional
comment “/AWC” is added at the end of the remarks section of the PIREP.
An AWC-WEB/xxxx in the remarks indicates the PIREP was submitted by an airline dispatcher or CWSU
meteorologist directly to the AWC. The “xxxx” represents the airline abbreviation or ARTCC of the CWSU
that submitted the PIREP.
Example:
PIREP TEXT/RM REMARKS/AWC
PIREP TEXT/RM REMARKS/AWC-WEB/KZFW
24.5.2 Aircraft Reports (AIREP)
AIREPs are messages from an aircraft to a ground station. AIREPs are normally comprised of the aircraft’s
position, time, FL, ETA over its next reporting point, destination ETA, fuel remaining, and meteorological
Chapter 24, Observations 24-34
information. It is beyond the scope of this document to describe the details of all the elements in the AIREP,
but this section will focus on the meteorological information.
The AWC’s website provides AIREPs over the CONUS and portions of the Atlantic and Pacific Oceans.
24.5.2.1 AIREP Types and Content
There are two types of AIREPs : routine or position report ( ARP) and special ( ARS). AIREPs can be
reported by the pilot, but the majority of routine AIREPs are automated and downlinked from the aircraft
to a service provider (e.g., a flight planning company) for processing and forwarding to an airline and the
NWS.
The majority of AIREPs report wind and temperature at selected intervals along the flight route, derived
from onboard sensors and probes. Some aircraft are equipped with sensors and probes to measure
humidity/water vapor, turbulence, and icing data.
The format for the AIREP is governed by the WMO and ICAO. The AWC’s website includes AIREPs on
their PIREP web page that is formatted for web display, with some weather elements decoded.
24.5.2.2 AIREP Examples
The following examples are from the AWC’s website. The actual airline ’s call sign was replaced with a
fictitious call sign, and the Special AIREP was created from the routine report.
24.5.2.2.1 Routine AIREP Example
ARP XXX836 2443N 15516W 2229 F350 M43 315/128 TB LGT
ARP Routine report.
XXX836 Aircraft call sign.
2423N 15516W Location in latitude and longitude, 24 ° and 23 minutes north, 155 ° and
16 minutes west.
F350 Flight level or altitude, FL350.
M43 Temperature in Celsius, minus 43°C.
315/128 Wind direction (reference to true north) and speed, 315° and 128 kt.
TB LGT Light turbulence.
24.5.2.2.2 Special AIREP Example
ARS XXX836 2443N 15516W 2229 F350 M43 315/128 TB SEV
ARS Special AIREP.
Same as the routine example except:
TB SEV Severe turbulence.
24.5.3 Volcanic Activity Reports (VAR)
The VAR (see Figure 24-6) is a report for aircraft encounters with volcanic ash and/or SO2 clouds. The first
part of the VAR is reported to ATC (as an Urgent PIREP or Special AIREP) as soon as practical. The
second part of the VAR is submitted postflight. The VAR is used by volcano scientists and forecasters to
better understand the characteristics of volcanic eruptions, including their volcanic ash and/or SO2 clouds.
Chapter 24, Observations 24-35
Additional information can be found in FAA Order 8900.1, Volume 3, Chapter 26, Section 7 , Safety
Assurance System: Volcanic Ash Avoidance, Concepts, Policies, and Guidance.
Figure 24-6. VAR Form
24.5.4 Turbulence Observations
Since the 1990s, several innovations have improved the quality and availability of turbulence reports.
Automated turbulence reporting systems are common on many commercial aircraft using the Aircraft
Meteorological Data Relay (AMDAR) system.
Modern commercial aircraft are equipped with meteorological sensors and associated sophisticated data
acquisition and processing systems. These systems continuously record meteorological information on the
aircraft and send these observations at selected intervals to ground stations via satellite or radio links where
Chapter 24, Observations 24-36
they are processed and disseminated.11 Participating airlines add turbulence information with these reports.
See Figure 24-7 for a plot of AMDAR reports from 2019.
AMDAR reports turbulence in terms of Eddy Dissipation Rate ( EDR). EDR is the ICAO standard
dimension for automated turbulence reporting. EDR is a state of the atmosphere measure rather than a state
of the aircraft measure, and is, therefore, independent of aircraft type.
Note: This information is restricted.
Figure 24-7. A Plot of AMDAR Reports Received During a 24-Hour Period in 2019
24.6 Radar Observations
24.6.1 Weather Surveillance Radar—1988 Doppler (WSR-88D) Description
Weather radar observations and their resultant images are graphical displays of precipitation and
non-precipitation targets detected by weather radars. WSR -88D, also known as NEXRAD, displays these
targets on a variety of products, which can be found on the websites of all NWS WFOs, the AWC, the SPC,
and websites and phone applications of various flight planning and weather service providers.
For information on radar basics, see Chapter 15, Weather Radar.
11 In 2019, it was estimated that NOAA was receiving about 600,000 wind and temperature observations per day,
with about 80 percent of the reports over the CONUS. This data comes from more than 9,000 aircraft.
Chapter 24, Observations 24-37
24.6.1.1 Issuance
WSR-88D radars are continuously generating radar observations. Each radar observation, called a volume
scan, consists of 5 to 14 separate elevation “tilts,” and takes between 4 and 11 minutes to generate,
depending on the radar’s mode of operation. Once one observation is complete, the next one begins. Radar
observation times are not standard nor are they synchronized with other radars. The valid time of the
observation is the time assigned to the product, which is the end of the last radar scan.
24.6.1.1.1 WSR-88D Radar (NEXRAD) Network
The WSR-88D radar network consists of 160 radars operated by the NWS, FAA, and DOD. Figure 24-8,
Figure 24-9, and Figure 24-10 show the locations of the radars.
Locations of WSR-88D weather radar are indicated by gray circles. Red circles indicate radars that are temporarily
out of service.
Figure 24-8. Locations of WSR-88D Weather Radar in the CONUS