The PIREP, the Only Weather Observation Made Inside the Airspace You Are About to Fly, and the Filing Skill That Could Save the Pilot Two Hours Behind You

A pilot weather report (PIREP) is the only real-time, first-hand observation of conditions inside the airspace you are about to fly through. Every other weather product in a standard briefing - METARs, TAFs, AIRMETs, surface analysis charts - is built from surface observations or forecast models. PIREPs are different: a pilot flew through that air and reported what they found. Knowing how to read them is a foundational cross-country skill. Filing your own when you land is a professional obligation.

Why Are PIREPs the Most Important Weather Product in Your Briefing?

Icing at 8,000 feet does not register on a ground sensor. Turbulence at cruise altitude produces no radar return. Whether a smooth layer of air sits above a rough stratus deck is not something a forecast model resolves with precision. Cloud tops - which determine whether you can climb above the weather - are often based on pilot estimates more than satellite data.

The only way any of that information reaches your briefing is if a pilot flew through it and filed a report. The entire system depends on a chain: pilots observe, pilots report, briefers collect it, and other pilots act on it. If any link in that chain breaks, the information disappears.

How Do You Find and Start Reading a PIREP?

PIREPs appear as blocks of coded text in a standard weather briefing, typically buried toward the end. They look like filing errors - rows of two-letter abbreviations, slash marks, identifiers, and numbers - until you know the key.

Every PIREP begins with either UA or UUA. UA is a routine pilot report. UUA is urgent - filed for severe turbulence, severe icing, or unusual phenomena like a tornado or waterspout sighting. When you see UUA, read it before anything else in the briefing.

What Do the PIREP Field Codes Mean?

After the UA/UUA designation, each field uses a two-letter code followed by a slash and the data. The major fields:

OV - Location. A VOR identifier, airport identifier, or position between two fixes. This tells you where in the route system the observation was made.

TM - Time. Four-digit Zulu. Weather moves. A PIREP filed six hours ago in a fast-moving frontal system may not describe what is there now. A fresh report is actionable. A stale one is background context only.

FL - Altitude in hundreds of feet. FL090 = 9,000 feet.

TP - Aircraft type. This matters more than it looks. A report of light turbulence from a Boeing 737 is not the same as light turbulence from a Cessna 172. Transport category aircraft absorb bumps that would feel moderate or worse in a light plane. When heavy iron reports light chop, consider what that means for your specific aircraft.

SK - Sky conditions and cloud tops as observed by the pilot. This field gives you base and top of cloud layers - information that is difficult to obtain from any other source. Tops determine whether you can climb above the weather and fly in smooth, clear conditions.

WX - Flight visibility and present weather. Uses the same codes as METARs.

TA - Outside air temperature at altitude, in Celsius. Combine this with the cloud layer location. When temperature runs between 0°C and approximately −20°C and the aircraft is in visible moisture, that is the primary icing envelope.

WV - Wind at altitude. Not a model output. Not a forecast. Observed.

TB - Turbulence. See intensity scale below.

IC - Icing. See intensity scale below.

RM - Remarks. Free text. Often the most useful part of the entire report. This is where pilots write in plain language what they found and what the next person should know: Tops smooth above 10,000. Icing worse northwest of the VOR. Smooth on top with good visibility. Read the remarks every time.

What Do the Turbulence Intensity Levels Mean?

The FAA standardizes turbulence reporting into four intensity levels.

Light turbulence produces slight, erratic changes in attitude and altitude. Occupants feel slight strain against seat belts. Unsecured objects may shift slightly. Manageable for a trained pilot in a light aircraft.

Moderate turbulence is greater intensity but the aircraft remains in positive control. Occupants feel definite strain against seat belts and unsecured objects get dislodged. In a Cessna or Piper, moderate turbulence demands focused flying - for passengers and for pilots without much turbulence experience, it can feel alarming.

Severe turbulence causes large, abrupt changes in altitude and attitude. The aircraft may momentarily be out of control. Occupants are forced violently against seat belts, and structural considerations come into play. A report of severe turbulence means you route around that airspace - not through it.

Extreme turbulence is rare. The aircraft is essentially uncontrollable and structural damage is probable. Treat airspace around an extreme turbulence report with the same respect you would give a severe convective SIGMET.

There is also a special designation: CAT (clear air turbulence). It appears in reports as something like moderate CAT. Clear air turbulence is invisible - no radar return, no associated cloud, often no visual warning. Jet stream boundaries are the classic source. Mountain wave can produce it at lower altitudes downwind of major ranges. When a PIREP mentions CAT at your altitude in mountain wave country, take it seriously.

How Do You Interpret Icing Reports in a PIREP?

The IC field covers both icing intensity and type.

Trace icing means ice is perceptible but accumulation is slight. Not immediately dangerous, but note it and stay alert.

Light icing means the accumulation rate could become a problem if you remain in it for over an hour. Start identifying exit options.

Moderate icing means the accumulation rate requires de-ice or anti-ice equipment if installed - or a divert. Brief exposure is hazardous to an unprotected aircraft. For a Cessna or Piper with no known icing protection, moderate icing is a diversion condition, not a press-on condition.

Severe icing means de-ice and anti-ice systems are failing to control the accumulation. Immediate diversion required. No deliberation.

Icing type also matters. Rime ice forms in stratiform clouds from small supercooled water droplets - porous, rough, and degrades lift. Clear ice (also called glaze ice) is denser, forms from larger droplets or freezing rain, and is aerodynamically more disruptive and harder to remove. Mixed icing combines both.

One point worth emphasis: when a PIREP reports unexpected icing in airspace where none was forecast, that observation carries real weight. The real atmosphere sometimes behaves outside the assumptions built into forecast models. That has produced catastrophic outcomes in the past and can still happen on an ordinary winter day over the Midwest.

How Do You Put Multiple PIREPs Together in a Real Briefing?

Consider a November flight from southern Illinois toward the Chicago area. Three PIREPs appear in the briefing, all filed within the past 90 minutes:

1. Cessna 172 over Midway Airport, 30 minutes ago, 6,000 feet: Broken layer, base 4,500 feet, tops 7,000 feet, OAT −3°C, light turbulence.
2. Beechcraft Bonanza over Bloomington-Normal, 1 hour ago, 8,000 feet: Light rime icing, OAT −5°C.
3. Boeing 737 over Midway Airport, 15 minutes ago, 8,000 feet: Severe turbulence. (UUA)

Put those together. There is a cloud layer from roughly 4,500 to 7,000 feet. Icing starts at 8,000 feet where the Bonanza was an hour ago - and with the temperature at −5°C and the system moving, that icing has likely intensified. A transport category jet is reporting severe turbulence at 8,000 feet, which in a light aircraft could feel extreme.

Your planned cruise altitude was 8,000 feet.

The smart move is to call flight service, ask specifically about AIRMETs and additional PIREPs for the route, and seriously reconsider departure time and altitude. Smooth air may exist above 10,000 or 11,000 feet above the layer - but if tops are rising ahead of the front, that option may close. Waiting two hours and letting the front push through could be the right call. These three reports have identified that 8,000 feet on this route right now is a problem. That is the system working exactly as intended.

How Do You File a PIREP?

In the United States, call 1-800-WX-BRIEF and tell the briefer you want to file a pilot report. Give your location, altitude, aircraft type, and observations. The briefer encodes it and puts it into the system. Every pilot briefing that route for the next hour will see your observation.

ForeFlight and other planning apps also have PIREP submission interfaces - same fields, plain language, submitted electronically.

The verbal format follows the same order as the coded format: location, time, altitude, aircraft type, sky conditions, weather, temperature, wind, turbulence, icing, remarks. Plain language works. The briefer does the encoding.

What Conditions Are Worth Reporting?

Report any of the following:

• Turbulence at moderate intensity or greater
• Any icing encounter, trace or above
• Significant deviations from forecast conditions
• Cloud tops notably higher or lower than forecast
• Ceiling or visibility notably different from the TAF

And this is something many student pilots miss: report good conditions too. A report of smooth air on top of a layer when the forecast was uncertain helps the next pilot make a better decision. Good news is still news.

Filing a PIREP takes about three minutes. The habit of reporting conditions - positive and negative - is one of the clearest marks of a pilot who understands they are part of the aviation system, not just operating inside it.

What Do Examiners Expect on the Private Pilot Checkride?

The Airman Certification Standards (ACS) require private pilot candidates to obtain, read, and correctly interpret aviation weather reports and forecasts, including pilot reports. Your examiner may present PIREPs as part of a cross-country planning scenario and ask what they mean for your route and altitude.

If a PIREP shows moderate icing along your planned route and your aircraft has no known icing protection, the examiner wants to see that you recognize it, understand the intensity scale, and factor it into your go/no-go decision. A pilot who can read a PIREP, understand what it means for their specific aircraft, and explain how it changes the plan has moved beyond memorization into genuine aeronautical decision-making.

Key Takeaways

• PIREPs are the only real-time, in-flight weather observations in a standard briefing - every other product is surface-based or model-generated.
• Always check the TM (time) field. A fresh report is actionable; a stale one in a fast-moving system is background context at best.
• Aircraft type matters: light turbulence from a Boeing 737 can be moderate or worse in a Cessna 172.
• For an aircraft with no ice protection, moderate icing is a diversion condition - not a reason to press on.
• Filing your own PIREP takes about three minutes and gives the next pilot real, first-hand information. That pilot may be a student on their first long cross-country.