PIREP Reports: Decoding Aviation Weather Observations
In the world of aviation, real-time data is critical for safety and efficiency. While automated systems provide a baseline, PIREPs (Pilot Reports) offer invaluable first-hand observations from pilots currently in the air. These reports allow other aircraft and air traffic controllers to understand the actual conditions of the atmosphere, from unexpected turbulence to icing levels.
While reporting standards can vary by country, the North American system provides a structured format to ensure that critical weather data is communicated clearly and concisely.
Key Facts
- UA identifies a routine report, while UUA indicates urgent, hazardous weather.
- Location is reported via NAVAIDs, airports, or precise latitude and longitude.
- Flight levels are recorded in hundreds of feet above sea level.
- Turbulence is categorized by intensity: Light (LGT), Moderate (MDT), Severe (SVR), or Extreme (EXTRM).
- Icing is classified by type (Clear, Rime, or Mixed) and accretion rate.
Understanding PIREP Identifiers and Location
The first piece of information in a PIREP is the message identifier, which immediately signals the urgency of the report. A UA identifier is used for non-hazardous weather. However, if a pilot encounters a tornado, funnel cloud, waterspout, severe turbulence, severe icing, hail, volcanic ash, or low-level wind shear, the identifier UUA is used to alert receiving agencies of a hazard.
The location (/OV) is reported using one of three methods: a direction and distance from a navigation aid (NAVAID), a direction and distance from an airport, or the aircraft's specific latitude and longitude.
Flight Data and Aircraft Specifications
Timing and altitude are essential for mapping weather patterns. The time (/TM) is always recorded in UTC (Coordinated Universal Time). The flight level (/FL) is typically a three-digit value representing altitude in hundreds of feet above sea level. In specific cases, abbreviations are used: DURD (during descent or on approach), DURC (during climb or after takeoff), or UNKN (unknown).
The aircraft type (/TP) uses the approved ICAO (International Civil Aviation Organization) designator to help other pilots understand how a specific aircraft size or weight might be reacting to the conditions.
Atmospheric Conditions and Visibility
Sky cover (/SK) describes cloud layers and their bases. Heights are listed in hundreds of feet above sea level. Common abbreviations include CLR (clear), FEW (few), SCT (scattered), BKN (broken), and OVC (overcast). For example, "BKN-OVC" indicates a range between broken and overcast.
Flight visibility and weather (/WX) combine visibility distance and current phenomena. Visibility is marked with FV followed by a two-digit value (rounded down), with FV99SM indicating unrestricted visibility. General weather phenomena follow a format similar to METAR (Meteorological Aviation Report).
Temperature (/TA) is reported in whole degrees Celsius. In the United States, negative temperatures are preceded by the letter M, while other regions use a minus (-) sign.
Wind, Turbulence, and Icing
Wind velocity (/WV) consists of a three-digit true direction and a three-digit wind speed in knots.
Turbulence (/TB) is reported based on the reaction of the aircraft and its occupants. It is categorized as LGT (light), MDT (moderate), SVR (severe), or EXTRM (extreme). Clear-air turbulence is specifically noted as CAT. Altitudes are provided in three-digit groups, using BLO (below) or ABV (above) if the exact boundaries are unknown.
Icing (/IC) is reported by type—CLR (clear), RIME, or MXD (mixed)—and intensity: TR (trace), LGT (light), MDT (moderate), or SVR (severe). All measurements are relative to Mean Sea Level (MSL).
Remarks and Specialized Reporting
The remarks section (/RM) captures conditions not covered in standard groups, such as St. Elmo's fire, thunderstorms, frontal conditions, or icing within precipitation. In the U.S., the FAA's SKYSPOTTER program trains pilots to provide enhanced observations; these reports are marked with /AWC at the end of the remarks.
| Code | Meaning | Category |
|---|---|---|
| UA / UUA | Routine / Urgent Hazard | Identifier |
| DURC / DURD | During Climb / During Descent | Flight Level |
| BKN / OVC | Broken / Overcast | Sky Cover |
| CAT | Clear-Air Turbulence | Turbulence |
| RIME / CLR | Rime Ice / Clear Ice | Icing Type |
Frequently Asked Questions
What is the difference between a UA and a UUA report?
A UA report is used for routine, non-hazardous weather information. A UUA report is used for urgent hazards such as tornadoes, severe icing, severe turbulence, or volcanic ash clouds.
How is flight level reported in a PIREP?
Flight level is usually a three-digit number representing altitude in hundreds of feet above sea level. If the aircraft is climbing or descending, DURC or DURD is used; otherwise, UNKN is used if the altitude is unknown.
What does CAT stand for in turbulence reports?
CAT stands for Clear-Air Turbulence, which refers to turbulence occurring in cloud-free air.
How is temperature recorded in U.S. PIREPs versus other regions?
In the United States, negative temperatures are preceded by the letter M. In other regions, a minus (-) sign is used to indicate temperatures below zero degrees Celsius.
What is the SKYSPOTTER program?
SKYSPOTTER is an FAA program that trains pilots to observe and report weather more accurately while in flight. These specialized reports are identified by the /AWC annotation in the remarks section.