How to Read a PIREP (and How to File One)

A PIREP is a pilot weather report: an observation from an airplane, coded into a fixed set of slash-separated fields so that a controller can type it and a briefer can read it. It is a report from inside the weather rather than from a sensor on the ground. The National Weather Service uses PIREPs to verify or amend its forecasts and advisories, and in some cases a pilot report is what triggers an advisory (AIM 7-1-18, AIM Basic with Change 3, effective July 9, 2026). The format is in section 24.5.1 of the Aviation Weather Handbook (FAA-H-8083-28B).

The PIREP decoded below was composed for illustration in the standard format. It is not a real report.

RDU UA /OV RDU180015/TM 1835/FL055/TP C172/SK BKN045-TOP060/WX FV05SM -RA/TA 08/WV 23025KT/TB LGT-MOD 040-055/IC NEG/RM DURD

A Cessna 172, 15 nautical miles south of the Raleigh-Durham VOR at 1835 UTC, descending through 5,500 feet MSL. It reported a broken layer based at 4,500 with tops at 6,000, flight visibility 5 statute miles in light rain, temperature 8 degrees Celsius, wind 230 magnetic at 25 knots, light to moderate turbulence between 4,000 and 5,500 feet, and no icing.

The fields come in a fixed order

Every PIREP carries the message type, location, time, altitude and aircraft type, then at least one weather element; fields with nothing to report are left out (FAA-H-8083-28B, 24.5.1). The AIM gives the same rule as items 1 through 6 in every transmitted PIREP plus one or more of items 7 through 13 (AIM 7-1-18, TBL 7-1-18). All altitudes are MSL unless noted. Visibility is in statute miles and every other distance is in nautical miles.

• RDU: the three-letter identifier of the weather reporting location nearest the phenomenon, added by the ground station (AIM TBL 7-1-18).
• UA / UUA: routine or urgent report (24.5.1.1).
• /OV RDU180015: location, the 180 radial at 15 NM from the RDU VOR. An identifier alone means overhead; two fixes joined by a hyphen, as in /OV KSTL-KMKC, describe a route segment (24.5.1.2). This is where the weather was, not where the airplane was when it called.
• /TM 1835: time of the encounter, four digits UTC (24.5.1.3).
• /FL055: altitude in hundreds of feet MSL where the phenomenon was first met, 5,500 feet; UNKN if not known (24.5.1.4). A climb or descent goes in the remarks as DURC or DURD.
• /TP C172: aircraft type. UNKN is allowed, but icing and turbulence reports always include the type (24.5.1.5).
• /SK BKN045-TOP060: sky condition, a broken layer based at 4,500 feet MSL with its top at 6,000. Layers are separated by a slash, a range of coverage by a hyphen (SCT-BKN050), and SKC after the last layer means clear above (24.5.1.6).
• /WX FV05SM -RA: flight visibility first, two digits rounded down to whole statute miles; FV99SM means unrestricted. Then weather in the METAR codes (24.5.1.7).
• /TA 08: outside air temperature in whole degrees Celsius, with M for negative, so /TA M08 is minus 8 (24.5.1.8).
• /WV 23025KT: wind, three digits of direction then speed in knots (24.5.1.9).
• /TB LGT-MOD 040-055: turbulence, with duration first if given, then intensity, then type, then altitude only if it differs from /FL (24.5.1.10).
• /IC NEG: icing, coded the same way; NEG means icing was forecast but not encountered (24.5.1.11).
• /RM DURD: remarks, here "during descent." Hazardous weather goes first in the remarks when there is any (24.5.1.12).

Base and top of a layer are the two numbers a VFR pilot wants most, and the two a surface observation does not give.

Altitudes are MSL, winds are magnetic, distances are nautical

Three unit conventions separate a PIREP from a METAR. Each is a trap. Cloud heights in a PIREP are MSL, because the pilot reads them off the altimeter; cloud heights in a METAR are AGL (FAA-H-8083-28B, 24.5.1 and 24.4.3.9). A PIREP of BKN045 over a field at 1,200 feet elevation puts the base about 3,300 feet above the field.

Wind is the second one. A PIREP wind is coded relative to magnetic north (24.5.1.9; AIM TBL 7-1-18 says "degrees magnetic north"), while a METAR or TAF wind is true (24.4.3.5), and so is the winds aloft forecast you compared it against. The two differ by the local variation.

Third, distances for position, as in RDU180015, are nautical miles, while flight visibility is statute miles (24.5.1).

UA and UUA: what makes a report urgent

A PIREP is coded UUA, urgent, when it reports tornadoes, funnel clouds or waterspouts; severe or extreme turbulence including clear air turbulence; severe icing; hail; low-level wind shear within 2,000 feet of the surface; volcanic ash; or anything the controller or flight service specialist taking the report considers hazardous to flight (FAA-H-8083-28B, 24.5.1.1.1). A wind shear report is urgent whenever it gives airspeed fluctuations of 10 knots or more, or gives no figure at all (24.5.1.1.1). Everything else is UA.

Air route traffic control centers broadcast an urgent PIREP alert once on all frequencies except emergency frequencies when any part of the area is within 150 miles of their airspace (AIM 7-1-8).

The turbulence intensity table

Turbulence is reported in four intensities. The AIM defines each by what the airplane does and what the people inside feel (AIM 7-1-21, TBL 7-1-21). Chop is the rhythmic kind.

The wording is condensed from AIM TBL 7-1-21, Turbulence Reporting Criteria Table; the AIM text is the reference when a report sits between two rows.

Duration uses three terms. Occasional is less than one third of the time, intermittent is one third to two thirds, and continuous is more than two thirds (TBL 7-1-21). Coded, these become OCNL, INTMT and CONS ahead of the intensity, so /TB OCNL MOD-SEV BLO 080 is occasional moderate to severe turbulence below 8,000 feet (FAA-H-8083-28B, 24.5.1.10). High-level turbulence, normally above 15,000 feet and not associated with cumuliform cloud, is reported as CAT with its intensity (TBL 7-1-21, note 1).

The aircraft type rides along with every turbulence report because the table describes reactions, and the air that nudges a Boeing moves a Skyhawk differently. Our reading: a MOD report from a jet deserves to be read as something worse by a pilot in a light trainer.

The icing intensity table

Icing intensity is defined by how fast ice accumulates and what the airplane's ice protection, if any, can do about it (AIM 7-1-19).

Definitions and rates are from AIM 7-1-19; the type codes RIME, CLR and MX, for rime, clear and mixed, are from the Aviation Weather Handbook (FAA-H-8083-28B, 24.5.1.11).

Read the light and moderate rows again with a trainer in mind. Both definitions assume a deicing system to cycle. Trace is the only row that does not. That is why the handbook says icing reports always include the aircraft type and should include the air temperature (24.5.1.5 and 24.5.1.11). The AIM also warns that a report of observed icing does not assure its presence or intensity later, and a report of no icing does not assure its absence (AIM TBL 7-1-20, Known Icing Conditions note). A 20-minute-old /IC NEG from a King Air is a data point, not a clearance.

How to give a PIREP by radio

Give it to whoever you are already talking to: flight service, the center or terminal ATC (AIM 7-1-18). The AIM says pilots should not be overly concerned with strict format or phraseology; the ground station will ask for anything that needs clarifying (AIM 7-1-18). For a turbulence report the AIM asks for location, time in UTC, intensity, whether in or near clouds, altitude or flight level, aircraft type and duration (AIM 7-1-21). Its own example reads: "Over Omaha. 1232Z, Moderate Turbulence, in cloud, Flight Level 310, B707" (TBL 7-1-21).

A report for the composed PIREP above might sound like this, given to Raleigh Approach. Suppose you say: "Raleigh Approach, Skyhawk 12345, pilot report. One five miles south of the Raleigh VOR, descending through five thousand five hundred, Cessna 172. Light to moderate turbulence from four thousand to five thousand five hundred. Broken layer, bases four thousand five hundred, tops six thousand. Five miles in light rain. Temperature plus eight. Negative icing." Every field the format needs is in there, and the controller will ask for anything missing.

For wind shear, state the airspeed loss or gain and the altitudes, and avoid "negative wind shear," which has been read as "no wind shear" (AIM 7-1-22). For anything above 15,000 feet in clear air, say CAT and give the intensity (AIM 7-1-23). Facilities are required to solicit PIREPs when ceilings are at or below 5,000 feet, visibility is at or below 5 miles, or thunderstorms, icing of light degree or greater, turbulence of moderate degree or greater, wind shear or volcanic ash are reported or forecast (AIM 7-1-18). Good weather is reportable too: a report of forecast conditions that did not occur helps the NWS verify its products (24.5.1).

Reports can also be filed after landing with flight service or a Weather Forecast Office (AIM 7-1-18), and online through the Aviation Weather Center, which requires a registered account validated against the FAA airman registry (AWC PIREP submission).

Reading PIREPs against your route

The AWC PIREP page lets you search by airport, radius and time window. Check /TM, because an hour-old report describes air that has moved. Check /OV against the chart, since it marks where the weather was (FAA-H-8083-28B, 24.5.1.2). Check /FL and the layer altitudes against your planned altitude, converting the MSL figures to height above the terrain you will cross. Check /TP before you believe any intensity.

Then put the reports next to the advisories. A /TB MOD inside an AIRMET Tango polygon confirms the forecast; a string of /TB NEG reports at your altitude does not cancel it, but it tells you what pilots are finding right now. AIRMET vs SIGMET covers the advisory side. FlyFren's free airport weather decoder shows the METAR and TAF at each airport along the way from the NWS Aviation Weather Center, as supplemental information rather than an official briefing. It does not replace the PIREPs that describe the air in between.

This article is educational and is not a substitute for the current regulations, the AIM, official weather briefings, or instruction from a CFI. Check the current text at the linked sources before you rely on any detail.