Any pilot can make a pilot weather report to air traffic control, who records the report and forwards it for dissemination to other pilots. Pilot reports, or PIREPS, often contain information about cloud bases and tops, turbulence, and wind shear.
They are written in coded text, like these example PIREPs:
Example: BDL UA /OV BDL /TM 2117 /FL008 /TP B737 /SK BKN009
Example: SYR UA /OV GGT /TM 2120 /FL310 /TP MD81 /TB LGT CHOP OCNL MOD
Example: HWV UUA /OV CCC180020 /TM 2125 /FLUNKN /TP A332 /TB SEV /RM SK-IFR WX-IMC DURD 140-125
Report Type
The first item of the PIREP is the type of report.
UA indicates a routine report, while UUA indicates an urgent PIREP. A PIREP is marked as urgent when a pilot reports a tornado, funnel cloud, waterspout, severe or extreme turbulence, severe icing, hail, volcanic ash, or low level wind shear.
Report Location
Next is the location, “OV” meaning over, followed by the Zulu time of the report.
Altitude
The altitude is given next, expressed as flight level and hundreds of feet.
Aircraft Type
The aircraft type then shown, followed by reported weather.
Example Decoded
In these examples we first have a report over Bradley VORTAC at 2117 Zulu at 800 feet by the pilot of a Boeing 737-700, who reports a sky condition of a broken cloud ceiling at 900 feet.
In the next report, over Georgetown three minutes later, the pilot of an MD81 reports light to occasional moderate chop at flight level three one zero.
The third pilot report is urgent, and was made 20 miles south of Calverton VOR. Three digit direction and distance are used when the pilot report is not made directly over a reference point. In this case, the reference point is Calverton VOR, and the report was made 180 degrees and 020 miles from the VOR, or 20 miles to the south. The report was made at 2125 Zulu by the pilot of an Airbus 330-200. The pilot reports severe turbulence, which is why the PIREP is urgent, but was not able to say for sure at what altitude the turbulence was encountered. The pilot adds a remark that instrument meteorological conditions were encountered during the descent from 14,000 to 12,500 feet.
A series of pilot reports can be used together to add a great deal of detail to the mental picture of the weather a pilot can expect to encounter during the flight.
More Examples
Other weather conditions that might be reported in a PIREP include flight visibility, weather limiting visibility, air temperature, wind, icing, and any plain language remarks made by the pilot.
Example: UA /OV APE090010/TM 1622/FL080/TP C172/SK OVC055-TOPUNKN/TA 04/TB NEG/RM IMC
In this example, a Cessna 172 ten miles east of Appleton at 1622 Zulu reports an overcast ceiling at 5,500 feet with tops which are unknown, since the pilot was still in the cloud layer at the cruising altitude of 8,000 feet. The air temperature, TA, is reported as positive four degrees. If the temperature were negative, it would be preceded by the letter M. Outside air temperatures are given in degrees celsius. The pilot reports negative turbulence at 8,000 feet, and remarks that the flight was being conducted in instrument meteorological conditions.
Example: GRK UA /OV LZZ /TM 2244 /FL085 /TP P28A /SK SKC /WX FV07SM
Here is a report by the pilot of a Piper Cherokee over Lampasas, Texas at 2244 Zulu at 8,500 feet, who reports clear skies and a flight visibility of seven statute miles.
Example: IOW UA /OV CID090020 /TM 2210 /FL065 /TP P28R /TA 20 /WV 30032KT /TB NEG
This pilot report from 20 miles east of Cedar Rapids at 2210 Zulu was made at 6,500 feet by the pilot of a Piper Cherokee, who reports an outside air temperature of positive 20 degrees Celsius and negative turbulence. This report also includes a wind velocity report. The pilot determined the winds at 6,500 feet were from 300 degrees at 32 knots.
Example: VGT UUA /OV VGT /TM 2331 /FL005 /TP P28A /TB MOD-SEV /RM LLWS DEP END RWY 25 500AGL
This PIREP is urgent, since it reports low level wind shear off the departure end of runway 25 at an altitude of 500 feet above the ground with moderate to severe turbulence. By reporting this information, this Cherokee pilot has saved the other pilots about to depart from the North Las Vegas Airport a big surprise on the initial climb out. Those pilots can now delay or cancel their flights in order to avoid this wind shear and turbulence.
Example: ELN UA /OV ELN315010 /TM 2225 /FL085 /TP C150 /WX FV05SM FU /TB LGT /RM FV 05-10 WESTBOUND
Here is a another PIREP that includes a report of flight visibility. This Cessna 150 pilot reports the flight visibility at five statute miles in smoke, FU meaning smoke. The pilot adds the remark that the flight visibility is between 5 and 10 miles when westbound.
Making a Pilot Report
In order to make pilot reports more usable and reliable, standards were created to guide pilots which terms to use when making a report.
Reporting Turbulence
Turbulence may be reported as light, moderate, severe, or extreme.
Light turbulence should be reported if slight changes occur in the airplane’s altitude and orientation, or attitude. In light turbulence unsecured items would be slightly displaced.
Report moderate turbulence if the turbulence is changing the airplane’s altitude and orientation significantly. The airspeed usually fluctuates in moderate turbulence, as well. Airplane occupants feel definite strain against seat belts, and unsecured objects are displaced.
Severe turbulence is violent, causing large, abrupt changes in altitude and attitude. Occupants experience violent forces against their safety belts, and unsecured objects are tossed about. In severe turbulence, the pilot may even momentarily lose control of the airplane.
Extreme turbulence means the airplane was almost impossible to control, and the pilot thinks the airplane may have been structurally damaged in the encounter with turbulence.
Reporting Chop
Pilots often report chop, instead of turbulence. Chop describes bumps which are more rhythmic, and do not really effect altitude and attitude. Chop may be reported as light chop or moderate chop. When a pilot reports chop, the word “CHOP” will be added to the PIREP.
Turbulence Frequency
Chop or turbulence is also described in terms frequency.
Pilots report the frequency and intensity of chop or turbulence together. For example, continuous moderate chop, or occasional light turbulence.
Reporting Icing
Reports of icing encounters are also standardized. Icing is reported as trace, light, moderate, or severe in intensity.
Trace icing means the rate of accumulation is very slight, and activation of deicing or anti icing equipment would not be necessary for at least an hour.
Light icing is reported if occasional use of deicing anti icing equipment removes or prevents accumulation, but may create a problem if encountered for more than one hour.
Moderate icing are potentially hazardous in even short encounters.
In severe icing, the deicing or anti icing equipment on the airplane fails to control the icing.
Icing types: