The PIREP, the Only Weather Report Written by Someone Who Was Actually There, and the Filing Habit Every Cross-Country Pilot Needs to Build Before the Next Flight

A PIREP - short for Pilot Weather Report - is an observation filed by a pilot who flew through actual conditions, not a forecast of what a model predicted. On a marginal weather day, a single recent PIREP describing actual cloud bases, tops, turbulence, or icing can clarify the picture faster than any prognostic chart. PIREPs are also among the most underused weather resources in general aviation.

What Is a PIREP and Why Does It Matter?

The full name is Pilot Weather Report. In the system, a routine report carries the identifier UA. An urgent report is UUA.

The urgent designation matters. A UUA gets priority handling and distributes quickly across the system. Pilots file a UUA when they encounter severe turbulence, severe icing, a tornado or funnel cloud, hail, or significant low-level wind shear. When you see a UUA in your briefing, treat it as a direct warning from another pilot - not a general advisory.

Most of what you’ll encounter in routine flying are standard UAs.

How Do I Read a PIREP? What Do the Field Codes Mean?

PIREP fields are separated by forward slashes. The encoding looks dense at first, but each field has a consistent meaning.

Here’s a decoded example: location over Oshkosh, time 1830Z, altitude 8,500 feet, aircraft type Cessna 172, sky condition broken ceiling at 2,000 feet clear above, temperature -4°C, turbulence light.

In raw format: UA /OV OSH /TM 1830 /FL085 /TP C172 /SK BKN020 /TA M04 /TB LGT

Field-by-field breakdown:

• /OV - Location. Usually a VOR or navaid identifier, or a bearing and distance from a fix. /OV ORD030015 means 15 miles northeast of O’Hare.
• /TM - Time, always in Zulu.
• /FL - Altitude in hundreds of feet. FL085 = 8,500 feet. FL250 = 25,000 feet.
• /TP - Aircraft type. This field carries more weight than it appears. A Boeing 737 crew calling conditions “light” may be describing a ride that would be moderate or worse in a Piper Cherokee. Heavy transport-category aircraft damp out bumps that toss light singles around. Always hold turbulence intensity against the airplane that filed it.
• /SK - Sky condition. Bases, tops, and coverage. When a pilot reports observed bases and tops, you’re getting the actual shape of the layer from someone who flew through it - something forecast models cannot provide.
• /WX - Significant weather: precipitation, smoke, volcanic ash, unusual visibility.
• /TA - Temperature in Celsius.
• /WV - Wind direction and speed at altitude.
• /TB - Turbulence.
• /IC - Icing.
• /RM - Remarks. Free text. A pilot who writes “heavy rain, lightning to the north, deviated 20 miles right” in the remarks field is giving you something worth reading carefully. This is often where the most operationally useful detail lives.

How Are Turbulence Intensity Levels Defined?

The intensity scale is standardized, though the reporters are human.

• Smooth - No turbulence.
• Light - Slight, erratic changes in altitude or attitude. Things shift in the cabin, nothing dramatic.
• Light chop - Rhythmic, repetitive bumpiness without significant altitude changes.
• Moderate - Changes in altitude and attitude, but the pilot maintains positive control. Unsecured objects will move. A person walking through a transport cabin would struggle to stay on their feet. The aircraft is still flying normally.
• Severe - Large, abrupt changes. The aircraft may be momentarily out of control. Occupants are thrown against their restraints. Structural damage is a real concern.
• Extreme - Violent tossing. Structural damage is likely.

For general aviation in light singles and twins, treat moderate turbulence as something to avoid when possible and prepare for when you can’t. Treat severe as a hard reason to turn around or divert immediately. The structural margins on a Cessna or Piper are not the same as a transport-category airplane.

Also pay attention to whether conditions were continuous or intermittent. A single jolt that got reported as moderate is a very different operational picture than continuous moderate turbulence. The remarks field often clarifies this.

One practical note: subjectivity in turbulence reporting goes in both directions. Some pilots underreport to avoid seeming dramatic; others overreport because a first solid bump in IMC conditions feels more intense than it is. Cross-reference multiple PIREPs along your route when available. A single data point is a clue. Three reports telling the same story is a pattern you can trust.

How Do I Interpret Icing Reports in a PIREP?

The icing intensity scale runs from trace to extreme:

• Trace - Barely perceptible accumulation. Slightly hazardous only in prolonged exposure.
• Light - Accumulation becomes hazardous over time if sustained. Manageable for properly equipped aircraft if exposure is limited.
• Moderate - Potentially hazardous even in short exposure. For most general aviation pilots flying singles without de-icing equipment, moderate icing is a no-go. Not a maybe. A no.
• Severe - Exceeds what even equipped aircraft can handle. Immediate diversion required. Life-threatening situation.

Icing type is also part of the report:

• Rime ice forms when small supercooled droplets freeze instantly on contact, producing a rough, milky white accretion concentrated on leading edges.
• Clear ice (also called glaze ice) forms from larger droplets that flow back before freezing. It’s denser, heavier, and spreads beyond leading edges in ways that can create irregular shapes on the airframe.
• Mixed is a combination of both.

Type matters because clear ice can accumulate in areas where your protection equipment doesn’t reach, and it weighs more per unit volume than rime. A report of clear ice tells a different story than a report of trace rime.

How Quickly Do PIREPs Go Stale?

Icing PIREPs go stale fast. The icing environment is dynamic - temperatures change with time of day, layers shift with frontal movement. A 2-hour-old icing PIREP tells you conditions existed at that time, not that they still do. A report from 30 minutes ago is operationally useful. Always read the timestamp as part of your analysis.

The same principle applies to turbulence in thermally active environments. Morning PIREPs over mountains in summer don’t reflect what you’ll find there at 2:00 p.m. when the thermals are firing.

Where Can I Find PIREPs During Flight Planning?

Leidos Flight Service includes relevant PIREPs in a standard briefing. If you’re not hearing them, ask directly: “Do you have any recent PIREPs along my route?” They have the data.

ForeFlight, Garmin Pilot, and similar EFB apps display PIREPs on the weather map as icons color-coded by turbulence and icing intensity. Tap one for the decoded report. The app does not remove stale data - checking timestamps is your responsibility.

aviationweather.gov has a dedicated PIREP search tool where you can filter by location, radius, altitude range, and time window. Pulling a strip of reports from departure to destination often reveals a trend that a single point observation would miss.

How Do I File a PIREP, and What Should I Report?

Most pilots don’t file PIREPs. They use them, benefit from them, and land without reporting. The PIREP database is only as good as the pilots who contribute to it. Every flight where conditions go unreported is information withheld from the next pilot behind you.

In the air, contact an Automated Flight Service Station on 122.2, or use the Flight Service frequencies listed on your sectional for your region. ForeFlight and Garmin Pilot both include a PIREP filing function that submits directly into the national database - select your fields, fill in what you observed, send. It takes about two minutes.

What to report: Location and altitude. Aircraft type. And whatever is notable.

• Smooth air at cruise altitude? Report it. A pilot at a lower altitude with a rough ride wants to know what’s waiting above.
• Confirmed cloud bases or tops? Report them.
• Ice - even trace, even if it dissipated quickly after a altitude change? Report it.
• Turbulence, any intensity? Report it.

After landing, you can still call Flight Service and file a postflight report. A report filed from the ramp still helps a pilot currently airborne over that same corridor.

How Do PIREPs Fit Into a Complete Weather Briefing?

PIREPs are one layer of a complete weather picture, not a replacement for it.

Cross-reference everything. AIRMETs and SIGMETs give you the broader hazard picture. Prognostic charts give you the trend. Aviation weather model output gives you the forecast. PIREPs tell you what was actually there. Use all of it together.

When a PIREP confirms what everything else is suggesting, you’re on solid footing. When a PIREP tells a different story than the rest of the picture, dig into the why before deciding which to trust. The Airman Certification Standards for private, instrument, and commercial all expect you to interpret weather products as a system - not as individual data points.

When you don’t have PIREPs, don’t treat the absence as clearance. It means nobody reported, not that conditions are smooth.

Key Takeaways

• A UUA (urgent PIREP) indicates severe turbulence, severe icing, a tornado, hail, or significant wind shear - take it seriously.
• Always match turbulence intensity to the aircraft type that filed the report; what a Boeing 737 calls light may be moderate in a Cessna.
• For unequipped general aviation aircraft, moderate icing is a hard no-go, not a judgment call.
• Check the timestamp on every PIREP - icing reports especially go stale within an hour as conditions shift.
• Filing a PIREP after your flight is how you return the favor to every pilot who filed one before yours.