Weather Alerts Explained
Understanding aviation weather advisories and what they mean for your flight.
Flight Chop displays several types of aviation weather products. Each serves a different purpose and has different implications for your flight. Understanding these can help you interpret what you see on the map and feel more informed about your journey.
PIREP (Pilot Report)
Blue circles (color varies by condition)Real-time actual conditions
What is it?
PIREPs are real-time reports submitted by pilots currently in the air. When a pilot encounters turbulence, icing, or other notable conditions, they radio a report that gets shared with other pilots and air traffic control.
What information does it contain?
- Aircraft type and flight level (altitude)
- Type and intensity of turbulence encountered
- Icing conditions if present
- Weather observations
- Time and location of the observation
What this means for your flight
PIREPs are actual conditions experienced by pilots, not forecasts. They are the most reliable indicator of what conditions are like right now. If you see turbulence PIREPs along your route, pilots on your flight will see them too and may adjust altitude to find smoother air.
Note: Urgent PIREPs (shown with red pulsing markers) indicate significant conditions that pilots need to know about immediately.
SIGMET (Significant Meteorological Information)
Red polygonsHigh - significant hazards
What is it?
SIGMETs are alerts issued for significant weather hazards that could affect all aircraft. These are the most serious weather advisories and cover conditions like severe turbulence, severe icing, volcanic ash, and widespread thunderstorms.
What information does it contain?
- Type of hazard (thunderstorms, turbulence, icing, etc.)
- Geographic area affected
- Altitude range
- Valid time period
- Movement and expected changes
Hazard Types
Thunderstorm activity
Severe turbulence area
Severe icing conditions
Ash from volcanic eruptions
Dust or sandstorms
What this means for your flight
If a SIGMET covers your route, pilots and airlines are fully aware. They will either route around the area, delay the flight if necessary, or change altitude to avoid the hazard. SIGMETs represent conditions that airlines take very seriously.
International SIGMET
Purple polygonsHigh - significant hazards (international airspace)
What is it?
International SIGMETs serve the same purpose as domestic SIGMETs but cover airspace outside the United States. They are issued by meteorological watch offices around the world and follow international standards set by ICAO (International Civil Aviation Organization). If you are flying internationally, these alerts show hazardous weather conditions along oceanic and foreign routes.
What information does it contain?
- Flight Information Region (FIR) affected
- Type of hazard (thunderstorms, turbulence, icing, volcanic ash, etc.)
- Altitude range (base and top)
- Valid time period
- Movement direction and speed
- Expected changes to the hazard
Hazard Types
Thunderstorm activity
Severe turbulence area
Severe icing conditions
Turbulence from mountain airflow
Ash from volcanic eruptions
Dust or sandstorms
What this means for your flight
For international flights, these are the primary weather alerts pilots monitor. Airlines flying overseas routes plan carefully around International SIGMETs, especially those involving volcanic ash or severe turbulence over oceans where diversion options are limited.
Note: Volcanic ash SIGMETs are particularly important for transoceanic flights. Aircraft must avoid volcanic ash entirely as it can cause engine failure. Routes are frequently adjusted when volcanic activity is detected.
G-AIRMET (Graphical Airmen Meteorological Information)
Orange polygonsModerate - notable conditions
What is it?
G-AIRMETs cover less severe but still significant weather conditions. They are issued every 6 hours with forecasts extending 12 hours ahead. These advisories help pilots plan around areas of moderate turbulence, icing, low visibility, and other conditions.
What information does it contain?
- Hazard type (turbulence, icing, low visibility, etc.)
- Forecast hours (+0h, +3h, +6h, +9h, +12h)
- Geographic area as polygons
- Altitude information
- Cause of the hazard (jet stream, mountain wave, etc.)
Hazard Types
Moderate turbulence expected
Moderate icing
Low visibility/clouds
Mountains hidden by weather
Thunderstorm development
Altitude where freezing begins
What this means for your flight
G-AIRMETs are useful for seeing what conditions are forecast along your route. They cover moderate conditions that may cause discomfort but are manageable. Pilots use these to choose smoother altitudes or make minor route adjustments.
CWA (Center Weather Advisory)
Green polygonsAdvisory - developing conditions
What is it?
CWAs are short-term forecasts issued by regional Air Route Traffic Control Centers. They fill the gap between scheduled forecasts and provide timely alerts about developing conditions. CWAs are valid for up to 2 hours.
What information does it contain?
- Developing weather conditions
- Area of concern within the center region
- Expected duration
- Type of hazard
What this means for your flight
CWAs indicate conditions that air traffic controllers are actively monitoring. They help pilots and controllers work together to manage developing situations before they become more serious.
How Pilots Use This Information
Before every flight, pilots receive a comprehensive weather briefing that includes all of these products. During flight, they receive updates from:
- Air Traffic Control: Controllers alert pilots to weather conditions ahead and can suggest altitude changes or route deviations.
- Company Dispatch: Airline dispatchers monitor weather continuously and communicate with pilots throughout the flight.
- Other Pilots: The PIREP system lets pilots share real-time conditions with each other via radio reports.
- Onboard Weather Radar: Most commercial aircraft have radar that shows precipitation and thunderstorms ahead.
Reading Raw PIREP Text
When you click on a PIREP marker, you will see a "Raw PIREP Text" section at the bottom. This is the original report as transmitted by the pilot. Here is how to decode it:
DEN UA /OV DEN090025/TM 1842/FL350/TP B737/TB MOD/RM CONT MOD CHOP
Decoded breakdown:
DENNearest station: Denver International AirportUAReport type: Routine PIREP (UUA = Urgent)/OV DEN090025Location: 25 nautical miles on the 090° bearing (east) from Denver/TM 1842Time: 18:42 UTC (Zulu time)/FL350Flight Level: 35,000 feet/TP B737Aircraft type: Boeing 737/TB MODTurbulence: Moderate/RMRemarks: Continuous moderate chopORD UUA /OV ORD180040/TM 2215/FL180/TP CRJ9/TB SEV/IC MOD-SEV RIME 160-190/RM SEVERE JOLTS
Decoded breakdown:
UUAUrgent PIREP - significant hazard reported/OV ORD18004040 nm south (180°) of Chicago O'Hare/TB SEVTurbulence: Severe/IC MOD-SEV RIME 160-190Icing: Moderate to Severe rime ice between FL160 and FL190 (16,000-19,000 ft)Common PIREP Codes Reference
Turbulence Intensity (/TB)
NEG- None (negative)LGT- LightMOD- ModerateSEV- SevereEXT- Extreme
Turbulence Type
CAT- Clear Air TurbulenceCHOP- ChoppyLLWS- Low Level Wind ShearMWAVE- Mountain Wave
Icing Intensity (/IC)
NEG- NoneTRC- TraceLGT- LightMOD- ModerateSEV- Severe
Icing Type
RIME- Rough, milky iceCLR- Clear, smooth iceMXD- Mixed rime/clear
Reading Raw SIGMET Text
SIGMETs use a structured format to convey hazard information. Here is how to interpret the raw text you see in the popup:
SIGMET CHARLIE 3 VALID UNTIL 2055Z TX OK FROM 30SSW OKC TO 40W DFW TO 50S SAT TO 30SSW OKC AREA SEV TS MOV FROM 25025KT TOPS ABV FL450
Decoded breakdown:
SIGMET CHARLIE 3SIGMET series Charlie, number 3 (series uses letters A-Z)VALID UNTIL 2055ZValid until 20:55 UTCTX OKAffects Texas and OklahomaFROM 30SSW OKC TO...Area defined by points: 30nm south-southwest of Oklahoma City, to 40nm west of Dallas, etc.AREA SEV TSHazard: Area of Severe ThunderstormsMOV FROM 25025KTMoving from 250° (west-southwest) at 25 knotsTOPS ABV FL450Storm tops above 45,000 feetSIGMET TANGO 2 VALID 1400-1800Z WA OR FROM SEA TO PDX TO EUG TO SEA SEV TURB BTN FL310 AND FL410 DUE TO JTSTR CONDS CONTG BYD 1800Z
Decoded breakdown:
VALID 1400-1800ZValid from 14:00 to 18:00 UTCWA ORAffects Washington and OregonSEV TURBSevere TurbulenceBTN FL310 AND FL410Between 31,000 and 41,000 feetDUE TO JTSTRCause: Jet StreamCONDS CONTG BYD 1800ZConditions continuing beyond 18:00 UTCCommon SIGMET Abbreviations
Hazard Types
TS- ThunderstormsSEV TURB- Severe TurbulenceSEV ICE- Severe IcingVA- Volcanic AshDS- DuststormSS- Sandstorm
Movement & Status
MOV- MovingSTNR- StationaryINTSF- IntensifyingWKN- WeakeningNC- No Change
Location Terms
BTN- BetweenABV- AboveBLW- BelowFL- Flight Level
Cause Terms
JTSTR- Jet StreamMWAVE- Mountain WaveCONVG- Convergence
The Key Takeaway
When you see weather alerts on Flight Chop, remember that pilots, dispatchers, and air traffic controllers are seeing the same information - and much more. The aviation system has multiple layers of monitoring and communication to ensure flights navigate weather safely. These alerts are tools for awareness, not reasons for alarm.