The PIREP, the Pilot Report That Fills the Gap Every Model Leaves Behind, and the Filing Habit That Makes You Part of the System

Every weather product in a standard preflight briefing - METARs, TAFs, winds aloft, prog charts - is generated by a model, a forecast, or a sensor that is not in the air. PIREPs, or Pilot Reports, fill the gap between what the atmosphere is forecast to do and what a pilot actually finds when they get up there. Learning to read them, apply them correctly, and file them yourself is one of the most practical weather skills you can develop.

Why PIREPs Exist

The METAR tells you surface conditions at a specific airport at the time of observation. The TAF tells you what a meteorologist forecasts for that airport over the next 24 to 30 hours. The winds aloft product gives you predicted speeds and directions at specific altitude bands, generated by numerical weather prediction models.

All of that is valuable. None of it tells you whether the smooth air shown on a graphic forecast actually held up over the terrain you are about to cross. None of it tells you what a pilot found when they climbed through a cloud layer at 6,500 feet over a specific ridgeline at two in the afternoon.

PIREPs do. A pilot, airborne, observing conditions in real airspace, reports what they find. Those reports are collected, coded, and distributed across the aviation weather system in near real time. They populate on the map at aviationweather.gov, appear in standard weather briefings from flight service, and load into most electronic flight bag applications.

Understanding the Two PIREP Types: UA vs. UUA

Every PIREP begins with one of two headers.

UA designates a routine pilot report. UUA designates an urgent pilot report - filed because conditions warranted immediate attention. Severe turbulence, severe icing, a waterspout, a tornado. Urgent PIREPs go directly to the National Weather Service and are treated with corresponding priority.

When you see UUA, stop and read that report before continuing your briefing.

How to Decode the Coded Fields

PIREPs are structured as a series of coded fields, each beginning with a forward slash and a two-letter identifier.

/OV - Location. Where the pilot was when they made the observation. This might be a VOR identifier, a bearing and distance from a navaid, or coordinates. /OV ABQ means the vicinity of the Albuquerque VOR. /OV ABQ 120025 means 120 degrees at 25 nautical miles from Albuquerque. A PIREP filed 150 miles off your route carries considerably less weight than one filed directly on it.

/TM - Time in UTC. The timestamp tells you how old the report is. Age matters enormously - more on this below.

/FL - Flight level or altitude. /FL080 means 8,000 feet MSL. /FL UNKN means the pilot was uncertain of their altitude.

/TP - Aircraft type. This field matters more than students initially give it credit for. A Piper Warrior reporting light turbulence is a different data point than a regional jet reporting the same thing. Icing accumulation on a light trainer with no ice protection is a fundamentally different threat than on an aircraft with certified deicing equipment. Filter every observation through the size and capability of the reporting aircraft relative to yours.

/SK - Sky conditions. Cloud layers the pilot observed. /SK BKN030 means broken clouds at 3,000 feet. /SK OVC060 means overcast at 6,000. /SK CLR means clear of clouds. Multiple layers are listed in sequence.

/WX - Weather. Standard codes: RA rain, SN snow, TS thunderstorm, FG fog. /WX FV99 means flight visibility 99 miles - essentially unrestricted.

/TA - Temperature in Celsius at altitude. One of the most important fields for icing assessment. Above 0°C in visible moisture, structural icing is generally not a concern. Below 0°C in clouds, you have a potential icing environment. This data comes from a source that was physically present at that altitude.

/WV - Wind at altitude. Speed and direction the pilot actually observed. Compare this against the winds aloft forecast to assess how well the model performed. When they align, confidence in the forecast rises. When they diverge, consider what else the model might be getting wrong.

The Turbulence Scale

The /TB field uses a standardized intensity scale.

• NEG - No turbulence encountered.
• LGT (Light) - Slight, erratic changes in attitude and altitude. Occupants feel slight strain against seatbelts. Walking is slightly difficult.
• MDT (Moderate) - Definite changes. The aircraft is momentarily out of control. Occupants feel definite strain against restraints. Loose objects are tossed. Walking is difficult.
• SEV (Severe) - Large, abrupt changes. The aircraft may be momentarily uncontrollable. Walking is impossible.
• EXTRM (Extreme) - The aircraft is violently tossed about, practically impossible to control, with the possibility of structural damage.

Frequency is also reported: Occasional (less than one-third of the time), Intermittent (one-third to two-thirds), Continuous (more than two-thirds). A report reading /TB MDT-SEV CONT means moderate to severe turbulence, continuously. That is not a minor data point.

The Icing Scale and Ice Types

The /IC field follows similar logic.

• NEG - No icing.
• TRC (Trace) - Ice is perceptible, but accumulation roughly equals sublimation. Not hazardous on its own unless the encounter is prolonged.
• LGT (Light) - Could become a problem if flight continues beyond about an hour.
• MDT (Moderate) - Even short encounters can become potentially hazardous. Ice protection systems must be used if available.
• SEV (Severe) - The rate of accumulation exceeds the ability of deicing equipment to reduce or control the hazard. Diversion required.

The type of ice matters as well. Clear ice forms a dense layer that adheres firmly to leading edges and disrupts airflow most seriously. Rime ice is more brittle and milky in appearance - less aerodynamically damaging but still a real hazard. Mixed combines both types.

/RM - Remarks. Plain English. The pilot can add anything that does not fit the coded fields: SMOOTH BELOW 4000, TOPS AT 9500, ICING CLEARED ONCE ABOVE CLOUD LAYER. Read remarks first if you are pressed for time - they often carry the most practically useful information in the entire report.

How Old Is Too Old? The PIREP Shelf Life Problem

A PIREP is a snapshot - one aircraft, one location, one moment in time. Weather moves and systems evolve.

PIREPs younger than one hour are generally considered current. Beyond that, treat them as background context rather than operational guidance, especially in rapidly changing conditions. In convective situations, a PIREP from 40 minutes ago may already be describing conditions that no longer exist.

The power of PIREPs comes from patterns, not individual reports. Multiple reports of icing in the same altitude band, filed within the past 45 minutes to an hour, is a much stronger signal than one isolated report from two hours ago. A single report showing negative turbulence does not mean the air will be smooth. A single report of severe turbulence does not mean you will find the same thing.

Use PIREPs in context with your other weather products.

Applying PIREPs to a Real Go/No-Go Decision

Consider a flight from central Kansas to Missouri - about 230 miles, in a Cessna 172, departing on a November afternoon. A cold front is stalled to the south. A low-pressure system is tracking northeast, well to the west.

The area forecast calls for scattered to broken clouds between 4,000 and 7,000 feet, with possible light icing in clouds above 6,000 feet due to near-freezing temperatures at altitude.

You pull up the PIREPs for your route and find this, filed 40 minutes ago by a Beechcraft Bonanza:

/FL070 /SK BKN045 OVC065 /TA 00 /IC LGT RIME CLR 060-070 /TB LGT OCSN /RM TOPS AT SIX EIGHT

Decoded:

• The Bonanza was at 7,000 feet
• Broken clouds at 4,500 feet, overcast at 6,500 feet
• Temperature exactly 0°C at 7,000 feet
• Light rime and clear icing between 6,000 and 7,000 feet
• Light, occasional turbulence
• Tops at 6,800 feet

Several critical pieces fall into place. The icing layer is confirmed, right where the area forecast placed it. The tops are only 300 feet above the overcast ceiling - climbing above them to escape the layer is not a realistic option at altitudes accessible to most light aircraft without supplemental oxygen on a long flight.

The Bonanza - heavier and faster than a Cessna 172 - reported light icing, not moderate, not severe. Here is where the aircraft type filter matters. The Cessna 172 is not certified for flight into known icing. Any intentional penetration of visible moisture where icing is known to exist is not a legal option. In your 172 with no ice protection systems, that light icing accumulates on the leading edges - and it is not a theoretical concern. The PIREP just converted the area forecast’s possible into a confirmed right now, on your route.

But the PIREP also showed tops at 6,800 feet. If conditions permit VFR below 4,500 feet, you can fly beneath the bases and stay clear of the icing layer entirely. Or you file IFR and request 8,000 feet, above the tops, where temperatures drop further and icing risk decreases.

That is PIREPs working exactly as designed - taking a model output labeled “possible” and converting it into a confirmed picture of what is actually out there.

Where PIREPs Fit in Your Briefing Workflow

PIREPs are the last layer you add. Build the big picture first: the synoptic pattern from the surface analysis, the forecast evolution from prog charts, terminal conditions from TAFs, the altitude environment from winds aloft. Understand what you expect to find.

Then pull the PIREPs and ask: What are the actual pilots finding out there right now?

That question closes the gap between forecast and reality. Every other product tells you what the atmosphere should be doing. The PIREP tells you what a pilot found when they went out and looked.

How to File a PIREP

Most student pilots read PIREPs. Very few file them - and that gap matters.

No special equipment or certification is required. If you are on flight following, key up and tell the controller: “I have a PIREP when you have time.” ATC routes it into the system immediately. If you are not on flight following, contact Flight Service on 122.2 or find a remote communications outlet on your sectional chart.

The format is flexible: aircraft type, location, altitude, what you are observing. The briefer or controller handles the coding.

Pilots consistently underreport three things:

1. Icing conditions - even light icing should be reported
2. Negative conditions - smooth air when turbulence was expected is genuinely valuable data
3. Cloud tops or bases that differ from the forecast - if you top out at 7,200 feet when the area forecast called for tops near 10,000, file it

The pilot two hours behind you on the same route is looking at the same area forecast, trying to make the same call you already made. File the PIREP they wish they had.

Key Takeaways

• PIREPs are the only weather product generated by a source that was actually in the air. They fill the gap no model, forecast, or surface sensor can close.
• UUA (urgent) PIREPs warrant immediate attention - read them before anything else in your briefing.
• Filter every PIREP through the reporting aircraft type. A light single reporting moderate turbulence is not the same data point as a regional jet reporting the same.
• PIREPs younger than one hour are generally current. Beyond that, use them as background context, not operational guidance - especially in convective conditions.
• Filing PIREPs is part of being a responsible pilot. If conditions surprised you - better or worse than forecast - take thirty seconds and file a report.