What a PIREP is
A Pilot Weather Report (PIREP) is an observation filed by a pilot currently in the air, describing actual conditions at a specific location, altitude, and time. PIREPs are the primary real-time source of in-flight weather observations — METARs report surface conditions, radar shows precipitation, but only a PIREP can tell you what's happening inside the cloud at 8,000 ft over a specific VOR right now.
Most PIREPs are voluntary. ATC and Flight Service frequently request them, especially in areas where conditions are reported as marginal or changing. Filed via radio with ATC or FSS and then distributed through the NWS and aviationweather.gov, PIREPs are available to all pilots in planning or in flight.
UA vs. UUA — Routine vs. Urgent
UA is a routine PIREP, filed when conditions are observed and worth sharing. UUA is an urgent PIREP, filed when a pilot encounters hazardous conditions that were not forecast or are significantly worse than forecast. Urgent PIREPs must be filed immediately with ATC or FSS and are given priority dissemination. They are required for:
- Severe or extreme turbulence
- Severe icing
- A tornado, funnel cloud, or waterspout
- Any other conditions hazardous to flight not previously reported
In preflight, treat a UUA on your route the same way you treat a SIGMET — it's a real aircraft reporting conditions hazardous enough to trigger an urgent filing. If the UUA was filed within the past 1–2 hours and the synoptic pattern hasn't changed, assume the conditions it describes are still there.
Where to find PIREPs
aviationweather.gov/pireps — primary source. Filter by area, altitude, time, and phenomenon type. Can display as text or as map overlays. Most EFB apps (ForeFlight, Garmin Pilot) pull from the same source and overlay PIREPs on moving maps. Request PIREPs from Flight Service during a standard weather briefing — they will pull any applicable reports for your route.
PIREP format decoded
PIREPs follow a standardized field structure using slash-separated codes. Not all fields are required — if a field is not observed or not applicable, it is omitted. The only required fields for a routine PIREP are location (/OV), time (/TM), altitude (/FL), aircraft type (/TP), and at least one weather element.
Example PIREP
Turbulence intensity scale
Turbulence intensity in PIREPs is reported using five standardized terms defined in the AIM. The definitions describe effects on the aircraft and occupants, not the meteorological cause. Two pilots in different aircraft can report different intensities in the same air mass — this is why aircraft type matters.
Smooth
No turbulence. Not typically reported in PIREPs except in remarks as confirmation of smooth conditions — useful when forecasts call for turbulence and you want to confirm they're wrong.
Light
Slight, erratic changes in altitude and/or attitude. Occupants may feel a slight strain against seat belts. Unsecured objects may be displaced slightly. Food and beverage service is possible. No significant loss of aircraft control.
Moderate
Similar to light turbulence but of greater intensity. Aircraft control is maintained but changes in altitude and/or attitude occur. Occupants feel definite strain against seat belts. Unsecured objects are dislodged. Food and beverage service is difficult.
Severe
Large, abrupt changes in altitude and/or attitude. Aircraft may be temporarily out of control. Occupants are forced violently against seat belts. Unsecured objects are tossed about. Food and beverage service and walking are impossible. Triggers a UUA filing requirement.
Extreme
Aircraft is violently tossed about and is practically impossible to control. May cause structural damage. Rare but documented. Any extreme turbulence PIREP on your route is an immediate go-around-level concern regardless of other factors. Requires UUA filing.
Aircraft type context is everything. A "light turbulence" report from a B737 may be moderate or severe in a Cessna 172. The larger the reporting aircraft relative to yours, the worse the actual conditions may be for you. When evaluating PIREPs, mentally upgrade the intensity by one level if the reporting aircraft is significantly larger than yours.
Icing intensity and type
Icing PIREPs report both intensity and type. The intensity describes the rate of accumulation relative to the deicing/anti-icing equipment's ability to handle it. The type describes the physical form of the ice — which affects aerodynamic impact and how quickly it accumulates.
Intensity
Trace
Ice becomes perceptible. Accumulation is slightly greater than sublimation. Not hazardous unless encountered for an extended period (more than one hour). Deicing equipment not required.
Light
Rate of accumulation may create a problem if flight continues longer than one hour. Deicing/anti-icing equipment will reduce or eliminate the accumulation. Pilots should plan a change of altitude or route.
Moderate
Rate of accumulation is such that even short encounters become potentially hazardous. Deicing/anti-icing equipment is or becomes inadequate for the accumulation rate. Immediate change of altitude or route is necessary.
Severe
Rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary. Any severe icing PIREP on your route requires a UUA filing by the reporting pilot and should be treated as a hard stop for any aircraft not certificated for flight in known icing.
Type
- Rime — forms when small supercooled water droplets freeze rapidly on contact with the aircraft surface. Opaque, rough, crystalline appearance. Less aerodynamically disruptive per unit of accumulation than clear ice but can build quickly on leading edges.
- Clear (Glaze) — forms when large supercooled droplets or freezing rain strike the aircraft and spread before freezing. Dense, transparent, difficult to remove. Conforms closely to aircraft surfaces and can spread beyond protected areas. Most aerodynamically hazardous type because it disrupts airfoil shape most effectively.
- Mixed — a combination of clear and rime, forming alternating or simultaneous layers. Common in areas where temperature and droplet size vary (near the 0°C layer, in convective clouds). Often most severe because it combines the hazards of both types.
Using PIREPs in preflight
Confirming or refuting forecasts
PIREPs are most valuable when they disagree with forecasts. If the GFA shows no icing along your route at 8,000 ft but three PIREPs from the past hour report moderate mixed icing at 7,000–9,000 ft along your route, trust the PIREPs. The models missed it, or the conditions evolved faster than the forecast cycle. Conversely, if an AIRMET Zulu covers your altitude and recent PIREPs report trace icing only, the AIRMET may be overstating the hazard — though "trace only" from a larger aircraft may still be meaningful for an unequipped single.
Cloud tops — one of the most valuable PIREP reports
The GFA estimates cloud tops; a PIREP reports them. If you're planning an IFR departure into a solid overcast, a PIREP reporting the tops at 9,000 ft means you know exactly how long you'll be in IMC before breaking out. A tops report is one of the most commonly useful pieces of PIREP data for IFR planning in IMC conditions. Check the age and location — tops can vary by thousands of feet over short distances near fronts.
Reading the age
The /TM field is the observation time, not the filing time. A PIREP observed at 1400Z and read at 1600Z is 2 hours old. In a rapidly evolving convective or frontal environment, a 2-hour-old PIREP may describe conditions that no longer exist. In a slowly changing stable airmass, a 3-hour-old PIREP may still be representative. Match the PIREP age to the rate of change of the underlying weather pattern.
The absence problem
No PIREPs does not mean clear conditions. It means no aircraft have filed reports from that area recently. A remote corridor with light traffic may have had no aircraft through it for hours regardless of conditions. An absence of icing PIREPs does not mean there's no icing. An absence of turbulence PIREPs does not mean smooth air. PIREPs fill in the picture; they cannot substitute for the base forecast when coverage is sparse.
Filing your own
You are expected to file PIREPs when you encounter conditions worth reporting — whether voluntarily or when ATC requests. A 30-second radio call reporting moderate turbulence at your altitude and location helps every pilot who follows you in that corridor. Technique: when ATC asks for a PIREP, report your location, altitude, aircraft type, and the phenomenon in that order. If unsure of the encoding, plain language is acceptable — controllers will format it for distribution.
Red flags
UUA on your route
An urgent PIREP for severe turbulence or severe icing means a pilot in an actual aircraft had conditions bad enough to require immediate filing. Treat it as a SIGMET until the pattern shows clear evidence of improvement. The pilot who filed it did not do so for convenience.
Icing report from a larger aircraft
Moderate icing reported by a B737 or turboprop is likely severe icing for an unequipped single. A "light rime" PIREP from a Citation may be moderate or worse in a C172. When the reporting aircraft is significantly larger than yours, upscale the reported intensity by at least one level before making your go/no-go decision.
Severe turbulence altitude near your planned level
Severe turbulence at 9,000 ft while you're planning 8,000 ft — that's one altimeter setting's worth of difference. The turbulence layer is not a precisely bounded box. If a SVR report is close to your altitude, treat it as covering your altitude unless a recent PIREP explicitly at your altitude shows a better ride.
Tops reported above your planned cruise altitude
If PIREPs show cloud tops at 14,000 ft and you're planning a VFR cruise at 9,500 ft, you need a new altitude or a new plan. For IFR: knowing the tops lets you calculate whether oxygen is needed on top, and whether your aircraft can get above the cloud in the first place.
PIREP contradicts the TAF
A TAF showing CAVOK at your destination while a PIREP from 45 minutes ago reports 3 SM visibility in fog at that airport means the TAF is already wrong. The METAR will confirm, but a contradicting PIREP is an early warning that the TAF forecast may have missed the timing of a phenomenon. Pull the current METAR before continuing the approach.
No PIREPs in a normally busy corridor
If a route that normally generates PIREPs has none in the past 3 hours, ask why. The traffic may have diverted around it, which is itself a signal. Check NOTAMs and ATC advisories. Sometimes the silence is because the weather is so bad no aircraft have been through — not because the weather is fine.
Checkride questions
Q: What is a PIREP and what are the two types?
A PIREP (Pilot Weather Report) is an in-flight weather observation filed by a pilot describing actual conditions at a specific location, altitude, and time. UA is a routine PIREP; UUA is an urgent PIREP. Urgent PIREPs must be filed immediately and are required when a pilot encounters severe or extreme turbulence, severe icing, or any other conditions hazardous to flight that were not previously forecast. Both types are distributed through ATC, FSS, and aviationweather.gov. (AIM 7-1-20)
Q: What are the required fields in a PIREP?
The required fields for a routine PIREP are: /OV (location), /TM (time), /FL (altitude), /TP (aircraft type), and at least one weather element. All other fields (/SK, /WX, /TA, /WV, /TB, /IC, /RM) are included as observed. For an urgent PIREP, the same fields are required plus the specific hazard being reported. (AC 00-45H §8.1)
Q: What are the five turbulence intensity levels used in PIREPs?
Smooth (NIL), Light (LGT), Moderate (MOD), Severe (SVR), and Extreme (EXTM). Smooth has no turbulence. Light produces slight, erratic changes in altitude and attitude. Moderate produces similar but stronger effects; occupants feel definite strain against seat belts. Severe produces large abrupt changes and may temporarily leave the aircraft out of control. Extreme makes the aircraft practically impossible to control and may cause structural damage. Both severe and extreme require an urgent PIREP. (AIM 7-1-21)
Q: What is the difference between rime and clear (glaze) ice?
Rime ice forms when small supercooled water droplets freeze rapidly on contact with the aircraft surface — producing a rough, opaque, milky-white deposit. Clear ice (also called glaze ice) forms when large supercooled droplets or freezing rain strike the aircraft surface and spread before freezing — producing a dense, transparent layer that conforms closely to the aircraft's shape and can extend beyond protected areas. Clear ice is generally more aerodynamically hazardous because it more effectively disrupts the airfoil profile and is more difficult to remove. Mixed ice combines characteristics of both. (AC 00-6B Ch. 10; AIM 7-1-21)
Q: Why is aircraft type important when reading a turbulence or icing PIREP?
Turbulence intensity is defined by its effect on aircraft and occupants — but larger aircraft are more resistant to those effects. Moderate turbulence in a Boeing 737 may produce severe effects in a Cessna 172. Similarly, icing that is manageable for a turboprop with pneumatic deicing boots may be severe for an unequipped piston single. Always note the /TP field and, if the reporting aircraft is significantly larger than yours, mentally upgrade the reported intensity by at least one level when evaluating the hazard. (AIM 7-1-21)
Q: Does the absence of PIREPs along a route mean conditions are clear?
No. An absence of PIREPs means no aircraft have filed reports from that area recently — it does not indicate clear or smooth conditions. A remote or lightly trafficked corridor may have had no aircraft through it in hours regardless of conditions. PIREPs supplement the base forecast; they cannot substitute for it when coverage is sparse. Always evaluate the full briefing (AIRMETs, GFA, TAF, AFD) and treat the absence of PIREPs as an information gap, not a green light. (AC 00-45H §8.3)
Q: What is the /SK field in a PIREP and why is it valuable for IFR planning?
The /SK field reports observed sky conditions — cloud base height, coverage, and tops (if the pilot was above the clouds). It is one of the few sources of actual cloud top data, compared to forecast-based estimates in the GFA. A PIREP reporting tops at 9,000 ft gives an IFR pilot concrete information about how long they will be in IMC, whether an on-top altitude is achievable, and whether oxygen equipment will be needed for the route. Forecast cloud tops can be off by thousands of feet; an observed PIREP tops report is operationally authoritative. (AC 00-45H §8.2)
Would-You-Fly scenario
Educational example only — this teaches the questions a pilot should ask, not a specific flight decision
You're planning an IFR cross-country in a Cessna 172S (not equipped for known icing) at 8,000 ft. The briefing shows AIRMET Zulu active along your route from 6,000 to 12,000 ft for moderate icing. The GFA shows a moist stable airmass with tops forecast near 10,000 ft. You pull PIREPs for the past 2 hours along your route and find the following:
- 2 hours ago — BE36 (Beechcraft Bonanza): MOD MXD icing, 7,000–9,000 ft. /RM: DURD, anti-ice on entire descent.
- 1 hour 10 minutes ago — C208 (Cessna Caravan, turboprop): LGT RIME 8,000 ft. /RM: CONT, no issues.
- 45 minutes ago — C172 (same type as yours): MOD CLR icing 7,500 ft, diverted. /RM: Unable maintain altitude.
How do you read these PIREPs and what do they tell you?
- The Bonanza (2 hrs ago) — moderate mixed icing: A BE36 is a pressurized, de-ice equipped aircraft. Its "moderate" report should be read as at least moderate for your 172. Anti-ice required throughout the descent means the icing layer was continuous and significant. This PIREP is 2 hours old — concerning, but conditions may have evolved.
- The Caravan (1 hr 10 min ago) — light rime: A turboprop Caravan has full de-ice equipment and is operated by professional crews. Its "light rime" is the most optimistic report in this set — but a C172 without icing equipment should not interpret a Caravan's "light" as safe for an unequipped aircraft. The ice is still there.
- The C172 (45 min ago) — moderate clear ice, diverted: This is your aircraft type. Same airframe. Moderate clear icing at 7,500 ft. The pilot could not maintain altitude and diverted. This PIREP is 45 minutes old — recent enough to be highly relevant in a slowly evolving stable airmass. This is an urgent-level signal for an identical aircraft.
No-go. A C172 pilot — the same aircraft you're flying — encountered moderate clear icing 45 minutes ago and diverted because they could not maintain altitude. Your aircraft is not certified for flight in known icing. AIRMET Zulu confirms the icing layer is forecast. There is no indication from the PIREPs that conditions have improved. The more optimistic Caravan report does not override the C172 PIREP — it reflects a different aircraft with de-icing equipment. Flying this route now, in an unequipped 172, into a confirmed icing layer that caused an identical aircraft to divert, is not a judgment call. It is a clear no-go.