Short answer: A PIREP (pilot weather report) is a short report from a pilot describing the weather they actually met in flight, such as smooth air, light chop or moderate turbulence, at a given place, time and altitude. A SIGMET (significant meteorological information) is an official warning from a weather office about hazardous weather, like severe turbulence or thunderstorms, so airlines can plan around it.
Key facts
- In the US, a SIGMET is a warning of hazardous en route weather and has the highest priority of all aviation weather products [1].
- A regular US SIGMET covers severe or greater turbulence, severe icing, widespread dust or sandstorms, or volcanic ash, and is valid for up to 4 hours [1].
- Convective SIGMETs (for thunderstorms) are issued every hour for three regions of the lower 48 states and are valid for 2 hours [1].
- PIREPs are coded as routine (UA) or urgent (UUA) [2][3].
- In one hour in July 2016, only a few dozen PIREPs were filed across the US, a small number next to the traffic in the sky [4].
- Of the US airlines the NTSB interviewed, all prohibited dispatchers from routing aircraft into areas of forecast severe turbulence [5].
What is a PIREP?
A PIREP, or pilot weather report, is a brief report from a pilot describing the weather they observed in flight [6]. Pilots give it by radio to air traffic control, to flight service or to their airline, or type it into a datalink or web tool, and it's then shared in a standard coded format [6].
PIREPs are real observations, not predictions. Other pilots and airline dispatchers use them to plan routes, controllers use them to manage traffic, and National Weather Service meteorologists use them to check and correct their forecasts [6]. The NTSB notes that a single PIREP can influence a forecaster's decision to issue or cancel a SIGMET [4].
Reports of smooth air count too. The NTSB encourages pilots to report light, "as forecast" and no-turbulence conditions, because they help controllers decide whether an altitude is fine to use again [4].
How to read a PIREP
Here is a real PIREP, quoted in an NTSB report [6]:
JAN UA /OV MHZ - IGB - MEI - MHZ/TM 1405/FL240/TP MULTIPLE/TB MOD 240-340/RM ZME
| Code | What it means | In this report |
|---|---|---|
| JAN | The station that entered the report | Jackson, Mississippi |
| UA | Routine report (UUA means urgent) | Routine |
| /OV | Where it happened: a point, an area, or a bearing and distance from an airport [3] | An area drawn between three navigation points |
| /TM | Time, in UTC [3] | 14:05 UTC |
| /FL | Altitude, three digits in hundreds of feet [3] | 24,000 feet |
| /TP | Aircraft type [3] | Several aircraft |
| /TB | Turbulence: intensity, how often, sometimes the type [2] | Moderate, between 24,000 and 34,000 feet |
| /RM | Remarks [3] | A control center code |
Turbulence intensity uses the words LGT (light), MOD (moderate), SEV (severe) and EXTRM (extreme); how often uses INTMT (intermittent), OCNL (occasional) and CONS (continuous); a range is written with a hyphen, like MOD-SEV; and NEG means no turbulence at all [2]. Turbulence reports must always include the aircraft type [2], because the intensity is judged from how that particular aircraft and its cabin respond [5].
What do those words feel like in the cabin? The FAA's reporting criteria say that in light turbulence occupants may feel a slight strain against their seat belts and food service can usually continue; in moderate turbulence they feel definite strains, and walking and food service become difficult [5]. Our guide to turbulence levels goes through each one.
Why PIREPs are useful but imperfect
PIREPs are human judgments, so they vary. One study found the location in turbulence PIREPs differed from automated aircraft data by an average of 25 miles, and another found that 10% to 20% of turbulence PIREPs had formatting errors [5]. They are also sparse: the NTSB counted only a few dozen nationwide in one hour in July 2016 [4].
Some airliners also send automated turbulence reports from their own sensors. These measure the eddy dissipation rate (EDR), which is the official turbulence intensity metric recognized by the International Civil Aviation Organization [5]. EDR data is more objective, and researchers told the NTSB that more of it should be shared [5].
What is a SIGMET?
A SIGMET (significant meteorological information) is a warning, in abbreviated plain language, about hazardous en route weather that may affect the safety of aircraft [1]. It's meant for all aircraft, from small planes to airliners [2]. A weaker cousin, the AIRMET (shown in the US as a graphic called a G-AIRMET), covers conditions that matter but don't meet SIGMET criteria, such as moderate turbulence [1].
| Product | Issued for | Valid for |
|---|---|---|
| SIGMET (US) | Severe or greater turbulence, severe icing, widespread dust or sandstorms, volcanic ash [1] | Up to 4 hours [1] |
| Convective SIGMET (US lower 48) | A line of storms at least 60 miles long, large areas of strong storms, or embedded or severe storms; a special one for tornadoes, hail of 3/4 inch or more, or gusts of 50 knots or more [1] | 2 hours, reissued hourly [1] |
| International SIGMET | Thunderstorms, severe turbulence, severe icing, dust or sandstorms, volcanic ash, tropical cyclones [1] | Up to 4 hours; 6 hours for volcanic ash and tropical cyclones [1] |
| G-AIRMET (US) | Moderate turbulence, strong surface winds, moderate icing, low clouds and poor visibility [1] | Up to 6 hours, issued every 6 hours [1] |
Outside the US, SIGMETs follow the international coding standard and cover a defined flight information region [2]. Weather offices around the world issue them, which is why SIGMETs exist for oceans and other continents too [7].
How to read a SIGMET
This example comes from the National Weather Service's own instructions [1]:
SIGMET ROMEO 2 VALID UNTIL 051000 ME NH VT FROM CAR TO YSJ TO CON TO MPV TO CAR SEV TURB BLW 080. RPRTD BY ACFT. CONDS CONTG BYD 1000Z.
- SIGMET ROMEO 2: the series name and its number.
- VALID UNTIL 051000: valid until 10:00 UTC on the 5th of the month.
- ME NH VT: the states affected: Maine, New Hampshire and Vermont.
- FROM CAR TO YSJ…: the area, drawn as a shape between navigation points.
- SEV TURB BLW 080: severe turbulence below 8,000 feet.
- RPRTD BY ACFT: the turbulence was reported by aircraft, in other words by pilots.
- CONDS CONTG BYD 1000Z: conditions are expected to continue beyond 10:00 UTC.
That's how the two work together: pilots report what they feel, and forecasters turn those reports into warnings for everyone else. National Weather Service meteorologists told the NTSB that most turbulence SIGMETs are only issued after a PIREP is reported [5].
What a SIGMET on your route means for you
A SIGMET is a heads-up for the people who plan and fly your trip, not a verdict on your flight. Here is what happens with that information:
- Dispatchers plan around it. Every airline the NTSB interviewed prohibited its dispatchers from routing aircraft into areas of forecast severe turbulence [5].
- Pilots keep their distance from storms. FAA guidance tells pilots to avoid any thunderstorm identified as severe, or giving an intense radar echo, by at least 20 miles [5].
- Crews get updates in the air. US airline dispatchers are required to give flight crews updated weather information during the flight, often by datalink [5].
- Airlines see more than you do. Dispatchers mostly use commercial turbulence forecasts built for airline flying, alongside the public SIGMETs [5].
The one thing that's yours to do is simple: keep your seat belt fastened whenever you're seated. In the NTSB's review of 111 turbulence accidents on US airlines from 2009 to 2018, only 1 of the 123 seriously injured people was documented as wearing a seat belt [5]. If you'd like the full picture, read is turbulence dangerous? and what causes turbulence.
Where to see PIREPs and SIGMETs yourself
The Aviation Weather Center at aviationweather.gov publishes both for free. SIGMETs cover the whole world, while pilot reports come primarily from the US and the North Atlantic [7]. The raw codes are terse, so some apps translate them; our roundup of turbulence apps compares them.
How Sorapuff helps
Sorapuff's route turbulence forecast reads the SIGMETs and the last three hours of pilot reports along your route from aviationweather.gov and adds them to its forecast from NOAA's GFS weather model, in plain words. "Severe" only ever appears when an official SIGMET says so. Pilot reports are sparse outside the US and North Atlantic, and every forecast is a likelihood, never a promise. Sorapuff Pro adds a route map showing storm areas and pilot reports.
FAQ
What does PIREP stand for?
PIREP stands for pilot weather report (often shortened to "pilot report"). It's a brief, coded message describing the weather a pilot actually met in flight: where, when, at what altitude, in which aircraft type, and what it was like, such as turbulence, icing, clouds or wind. Meteorologists, dispatchers, controllers and other pilots all use PIREPs to check forecasts and plan routes.
What is the difference between a SIGMET and an AIRMET?
A SIGMET warns of hazardous weather, such as severe turbulence, severe icing, volcanic ash or, in a convective SIGMET, strong thunderstorms. An AIRMET covers weather that matters but is less intense, such as moderate turbulence, moderate icing or low clouds. In the US, a regular SIGMET is valid for up to 4 hours and a G-AIRMET for up to 6 hours.
Should I worry if there is a SIGMET on my route?
Usually not. A SIGMET is there so the people planning your flight can avoid that area or altitude. The airlines the NTSB interviewed don't let dispatchers route flights into forecast severe turbulence, and FAA guidance tells pilots to stay at least 20 miles from severe storms. A SIGMET covers an area and a range of altitudes, and your flight may pass above, below or around it. Keep your belt fastened and always follow your crew.
What does UUA mean in a pilot report?
UUA marks an urgent PIREP, one that describes weather that is a hazard or potential hazard to flight, such as severe turbulence, severe icing, hail or strong wind shear. Urgent reports get priority handling so they reach controllers and other pilots faster. A routine report is coded UA.
Can passengers see pilot reports for their flight?
Yes. The Aviation Weather Center publishes current pilot reports and SIGMETs for free at aviationweather.gov, and some apps show them along your route. Keep in mind that reports are sparse, mostly from the US and North Atlantic, and each one describes a single moment in a single aircraft. Your crew has more data than any public map.
Sources
- NWS Instruction 10-811, En Route Forecasts and Advisories (September 2, 2025), National Weather Service
- AWC Product Info: PIREPs, SIGMETs and G-AIRMETs, Aviation Weather Center
- PIREP Submission Information, Aviation Weather Center
- Safety Alert SA-064, Pilot Weather Reports (PIREPs): Pay It Forward (June 2017), NTSB
- Preventing Turbulence-Related Injuries in Air Carrier Operations, Safety Research Report SS-21/01 (2021), NTSB
- Improving Pilot Weather Report Submission and Dissemination, Special Investigation Report SIR-17/02 (2017), NTSB
- Data API, Aviation Weather Center