11.1 METARs, SPECI, TAFs & PIREPs
Key Takeaways
- METAR and SPECI reports encode surface weather and operational safety elements, including low-level wind shear below 2,000 ft AGL (WS020/24045KT), Runway Visual Range (e.g. R04R/2600FT, R22L/P6000FT, R16C/1000V2000FT), and standardized present weather descriptors.
- Advanced METAR remarks contain critical flight planning data: sea level pressure in tenths of hPa (SLP142 = 1014.2 hPa, SLP982 = 998.2 hPa), high-precision temperature/dewpoint T-groups (T00441011 = +4.4°C / -1.1°C), peak winds (PK WND 28045/15), and variable ceilings (CIG 002V004).
- Terminal Aerodrome Forecasts (TAFs) cover 24-hour or 30-hour periods; rapid permanent changes are forecast using FM groups (From), temporary fluctuations lasting <1 hour and covering <50% of the period use TEMPO groups, and domestic FAA TAFs use PROB30 (30% probability) rather than PROB40 or BECMG.
- Pilot Weather Reports (PIREPs) are classified as Routine (UA) or Urgent (UUA); mandatory UUA criteria include severe or extreme turbulence, severe icing, hail, low-level wind shear (LLWS) with airspeed losses/gains of 10+ knots within 2,000 ft AGL, volcanic ash, and tornadoes/funnel clouds.
- Icing intensities (Trace, Light, Moderate, Severe) and turbulence classifications (Light, Moderate, Severe, Extreme) require standardized cockpit reporting; severe icing or severe turbulence mandates immediate operational diversion.
Last updated: August 2026
METARs, SPECI, TAFs & PIREPs
Core Airline Transport Principle: Accurate tactical and strategic flight planning in air carrier operations depends on absolute fluency in decoding aviation weather reports, forecasts, and pilot reports. Under 14 CFR Part 121, operating decisions—ranging from takeoff alternate requirements and derived landing minimums to enroute diversions—hinge upon specific meteorological values encoded in METARs, TAFs, and PIREPs.
1. METAR & SPECI Syntax, Structure & Issuance Criteria
A METAR (Aviation Routine Weather Report) is the standard international surface observation code generated hourly between 45 and 55 minutes past each hour. A SPECI (Aviation Selected Special Weather Report) is an unscheduled report issued immediately whenever specific, operationally significant weather changes occur between routine hourly reports.
+-----------------------------------------------------------------------------+
| ANATOMY OF A TRANSPORT METAR / SPECI |
| |
| METAR KJFK 161851Z 32024G38KT 280V350 3/4SM R04R/2600FT +TSRAGS FG |
| BKN008 OVC015CB 18/16 A2982 WS020/28055KT RMK AO2 PK WND 31048/42 |
| SLP098 T01780161 56012 P0018 $ |
| |
| [KJFK] Station Identifier (ICAO 4-letter code) |
| [161851Z] Date/Time: 16th day of month at 1851 UTC (Zulu) |
| [32024G38KT] Wind: 320° True at 24 kts, Gusting to 38 kts |
| [280V350] Variable Wind Direction: Between 280° and 350° (speed >= 6 kts)|
| [3/4SM] Prevailing Visibility: 3/4 Statute Mile |
| [R04R/2600FT] Runway Visual Range: Runway 04 Right is 2,600 feet |
| [+TSRAGS FG] Present Weather: Heavy Thunderstorm, Rain, Small Hail/Pellets, Fog|
| [BKN008 OVC015CB] Sky Condition: Broken 800 ft, Overcast 1,500 ft CB |
| [18/16] Temperature/Dewpoint: +18°C / +16°C |
| [A2982] Altimeter Setting: 29.82 inHg |
| [WS020/28055KT] Wind Shear: At 2,000 ft AGL, Wind 280° at 55 knots |
| [RMK ...] Remarks Section: Detailed sensor, pressure, and thermal data |
+-----------------------------------------------------------------------------+
Mandatory SPECI Issuance Thresholds
Automated observing systems (ASOS/AWOS) and human observers must immediately transmit a SPECI when any of the following operational parameters are breached:
- Ceiling Changes: A ceiling forms, disappears, or crosses above or below critical approach minimum thresholds: 3,000 ft, 1,500 ft, 1,000 ft, 500 ft, 200 ft (CAT I decision height), or the lowest published airport IFR landing minimum.
- Visibility Changes: Prevailing visibility decreases or increases across key regulatory milestones: 3 SM, 2 SM, 1 SM, 3/4 SM, 1/2 SM, or the lowest published landing minimum.
- Wind Shift: Wind direction changes by $45^\circ$ or more in less than 15 minutes, with sustained wind speeds of at least 10 knots.
- Hazardous Present Weather: Inception, cessation, or change in intensity of:
- Tornado, funnel cloud, or waterspout.
- Thunderstorm ($TS$).
- Freezing precipitation (freezing rain $-FZRA/FZRA$, freezing drizzle $FZDZ$).
- Ice pellets ($PL$) or hail ($GR/GS$).
- Squall ($SQ$).
- Runway Visual Range (RVR): RVR decreases below or increases above 2,400 feet (1/2 SM equivalent) on any active instrument runway within a 10-minute period.
2. Low-Level Wind Shear & Runway Visual Range (RVR) Encoding
Low-Level Wind Shear in the Body
When non-convective low-level wind shear is detected by terminal sensors (such as Low-Level Wind Shear Alert System [LLWAS] or Terminal Doppler Weather Radar [TDWR]) along the runway approach or departure corridor up to 2,000 feet AGL, it is encoded in the main body:
- Example:
WS020/24045KTindicates wind shear at 2,000 feet AGL with a wind vector of $240^\circ$ True at 45 knots. - Example:
WS010/18050KTindicates wind shear at 1,000 feet AGL with a wind vector of $180^\circ$ True at 50 knots.
+-----------------------------------------------------------------------------+
| RUNWAY VISUAL RANGE (RVR) SYNTAX MATRIX |
| |
| Encoded Format Operational Translation |
| ----------------------------------------------------------------------- |
| R04R/2600FT Runway 04 Right RVR is constant 2,600 feet. |
| R22L/P6000FT Runway 22 Left RVR exceeds 6,000 feet (P = Plus). |
| R16C/M0600FT Runway 16 Center RVR is below 600 feet (M = Minus).|
| R28/1000V2000FT Runway 28 RVR is variable between 1,000 & 2,000 ft.|
| R01L/1200V2400V0800FT Variable RVR across touchdown, mid, and rollout. |
| R09/2200U ICAO: Runway 09 RVR 2,200 meters, upward trend (U).|
| R27/1400D ICAO: Runway 27 RVR 1,400 meters, downward trend (D)|
| R33/1800N ICAO: Runway 33 RVR 1,800 meters, no change (N). |
+-----------------------------------------------------------------------------+
- RVR Measurement Systems: Transmissometers or forward-scatter meters measure visual range at Touchdown (TDZ), Mid-Point (MID), and Rollout (RO). In US operations, values are reported in hundreds of feet; internationally, values are in meters with trend indicators ($U$ = upward, $D$ = downward, $N$ = no change).
3. Present Weather Qualifiers, Descriptors & Obscurations
Present weather is constructed using a systematic combination of Intensity/Proximity, Descriptor, and Phenomena codes.
+-----------------------------------------------------------------------------+
| PRESENT WEATHER CODE CONSTRUCTION |
| |
| [Intensity / Proximity] + [Descriptor] + [Precipitation / Obscuration] |
| |
| Examples: |
| - -FZDZ = Light Freezing Drizzle |
| - +TSRASN = Heavy Thunderstorm with Rain and Snow |
| - VCBCHZ = Patches of Haze in the Vicinity (5 to 10 SM from airport) |
| - +BLSN = Heavy Blowing Snow (lifted >= 2 meters / 6 feet above ground)|
| - MIFG = Shallow Fog (depth < 2 meters / 6 feet above ground) |
| - PRFG = Partial Fog (covers part of the aerodrome) |
| - BCFG = Patches of Fog (random fog patches across aerodrome) |
| - FZFG = Freezing Fog (supercooled water droplets at temp <= 0°C) |
+-----------------------------------------------------------------------------+
Comprehensive Present Weather Matrix
| Category | Code | Meaning | Operational Notes |
|---|---|---|---|
| Intensity / Proximity | - | Light | Minimal rate of accumulation or reduction in visibility. |
| (none) | Moderate | Standard precipitation rate. | |
+ | Heavy | Significant accumulation, severe reduction in visibility. | |
VC | Vicinity | Weather phenomenon observed between 5 and 10 SM from station. | |
| Descriptors | MI | Shallow | Less than 2 meters (6 feet) deep. |
PR | Partial | Substantial part of aerodrome covered. | |
BC | Patches | Irregular patches over aerodrome. | |
DR | Low Drifting | Lifted by wind less than 2 meters above ground. | |
BL | Blowing | Lifted by wind 2 meters or more above ground. | |
SH | Showers | Convective precipitation with rapid starts and stops. | |
TS | Thunderstorm | Lightning / thunder detected within past 15 minutes. | |
FZ | Freezing | Supercooled liquid droplets freezing on impact. | |
| Precipitation | DZ | Drizzle | Very small droplets (diameter < 0.5 mm), slow fall speed. |
RA | Rain | Droplets diameter $\ge 0.5\text{ mm}$. | |
SN | Snow | Hexagonal ice crystals, aggregates, or flakes. | |
SG | Snow Grains | Very small, white, opaque grains of ice (equivalent of drizzle). | |
IC | Ice Crystals | Diamond dust, unbranched ice crystals floating in cold air. | |
PL | Ice Pellets | Frozen raindrops (sleet); indicates freezing rain aloft. | |
GR | Hail | Hailstones diameter $\ge 5\text{ mm}$ (1/4 inch). | |
GS | Small Hail / Snow Pellets | Diameter $< 5\text{ mm}$ (graupel). | |
UP | Unknown Precip | Automated sensor detected precipitation of undetermined type. | |
| Obscurations | FG | Fog | Visibility $< 5/8\text{ SM}$ ($< 1,000\text{ m}$), RH $\approx 100%$. |
BR | Mist | Visibility $5/8\text{ SM}$ to $6\text{ SM}$, RH $\ge 80%$. | |
FU | Smoke | Suspended combustion particles. | |
VA | Volcanic Ash | Extremely abrasive pulverized rock; flight hazard. | |
DU | Widespread Dust | Finely divided earth particles in suspension. | |
SA | Sand | Sand particles suspended in the atmosphere. | |
HZ | Haze | Dry particulate suspension, RH $< 80%$. | |
PY | Spray | Water droplets torn from wave crests by gale-force winds. | |
| Other | SQ | Squall | Wind increase $\ge 16\text{ kts}$, sustained $\ge 22\text{ kts}$ for $\ge 1\text{ min}$. |
FC | Funnel Cloud | Tornado or waterspout (+FC = tornado/waterspout touching surface). | |
SS / DS | Sandstorm / Duststorm | Visibility $< 5/16\text{ SM}$ in blowing sand or dust. | |
PO | Dust/Sand Whirls | Well-developed dust devils. |
4. Advanced Remarks (RMK) Decoding
The remarks section contains precision meteorological data critical for transport category operations, altimetry, density altitude, and frontal tracking.
+-----------------------------------------------------------------------------+
| PRECISION REMARKS DECODING GUIDE |
| |
| Remark Code Decoded Operational Information |
| ----------------------------------------------------------------------- |
| AO1 / AO2 Station type: AO1 = without precip discriminator; |
| AO2 = with liquid/frozen precip discriminator. |
| |
| PK WND 28045/15 Peak Wind: 280° at 45 kts occurred at 15 past hour. |
| |
| WND DATA EST Wind data estimated due to sensor malfunction. |
| |
| CIG 002V004 Ceiling variable between 200 ft and 400 ft AGL. |
| |
| CIG 005 RWY16 Ceiling 500 ft AGL specifically over Runway 16 sensor.|
| |
| SLP142 Sea Level Pressure: 1014.2 hPa (14.2 -> 1014.2). |
| SLP982 Sea Level Pressure: 998.2 hPa (98.2 -> 998.2). |
| * Rule: If 1st digit is 0-5, prefix with 10 (1000s). |
| * Rule: If 1st digit is 6-9, prefix with 9 (900s). |
| |
| T00441011 Precision Temp/Dewpoint: +4.4°C / -1.1°C. |
| * Format: T[sn][TTT][sn][TTT] |
| * sn = 0 (Positive) or 1 (Negative / Subzero). |
| * T0044 -> +4.4°C; T1011 -> -1.1°C. |
| * T10281056 -> Temp -2.8°C, Dewpoint -5.6°C. |
| |
| 56012 3-Hour Pressure Tendency: Code 5 (decrease then steady|
| or decrease), fell 1.2 hPa in past 3 hours. |
| |
| P0018 Hourly Precipitation Accumulation: 0.18 inches. |
| 60045 3- or 6-Hour Precipitation Accumulation: 0.45 inches. |
| 70120 24-Hour Precipitation Accumulation: 1.20 inches. |
| |
| PRESRR / PRESFR Pressure Rising Rapidly / Pressure Falling Rapidly |
| (>= 0.06 inHg or 2.0 hPa per hour). |
| |
| FROPA Frontal Passage occurred during observation interval. |
| VIRGA Precipitation aloft evaporating before reaching ground|
| CB DSNT NW MOV E Cumulonimbus distant northwest, moving east. |
| $ Maintenance indicator (sensor requires servicing). |
+-----------------------------------------------------------------------------+
5. Terminal Aerodrome Forecasts (TAF): Architecture & Rules
A TAF is a concise statement of expected meteorological conditions at an airport within a 5-statute-mile radius of the center of the runway complex. TAFs are issued 4 times daily (0000Z, 0600Z, 1200Z, 1800Z) by National Weather Service Weather Forecast Offices (WFOs).
+-----------------------------------------------------------------------------+
| TAF ANATOMY & STRUCTURE |
| |
| TAF KORD 161730Z 1618/1724 20015G25KT 5SM HZ BKN030 |
| WS020/22045KT |
| FM162200 24018KT 3SM +TSRA BKN015CB OVC030 |
| TEMPO 1623/1702 1/2SM +TSRAGS FG BKN005 OVC010CB |
| FM170300 32014KT P6SM SKC |
| PROB30 1708/1712 2SM BR BKN010 |
| |
| - Validity Period: 1618/1724 = Valid from 16th at 1800Z to 17th at 2400Z |
| (30-hour validity window for high-density international hub). |
| - Base Forecast: 200° at 15G25KT, 5 SM Haze, Broken 3,000 ft, |
| Low-level wind shear at 2,000 ft AGL from 220° at 45 kts. |
+-----------------------------------------------------------------------------+
Validity Periods: 24-Hour vs. 30-Hour TAFs
- 24-Hour TAFs: Standard for regional, domestic, and non-hub aerodromes.
- 30-Hour TAFs: Issued for designated major international gateways (e.g., KORD, KJFK, KLAX, KDFW, KATL) to support long-haul international flight dispatch under 14 CFR Part 121 Flag and Supplemental operations.
Change Group Rules & Definitions
+-----------------------------------------------------------------------------+
| TAF CHANGE GROUPS COMPARISON |
| |
| Group Code Duration & Probability Operational Rules |
| ----------------------------------------------------------------------- |
| FMddhhmm Permanent, rapid change - Full weather transition in |
| (From) occurring in < 1 hour. less than 60 minutes. |
| - Completely overwrites all |
| previous forecast lines. |
| - Requires 2-digit minute time|
| (e.g., FM162200). |
| |
| TEMPO Temporary fluctuations - Each instance lasts < 1 hr. |
| ddhh/ddhh expected for < 50% of the - Total duration < 50% of the |
| specified time window. prescribed TEMPO window. |
| - Only modified elements are |
| listed; unmentioned elements|
| revert to prevailing base. |
| |
| PROB30 30% Probability of - Represents 30% to 39% chance|
| ddhh/ddhh hazard or precipitation. of convective/IFR conditions|
| - Prohibited in first 9 hrs |
| of domestic US TAFs. |
| - Under standard Part 121, |
| PROB30 conditions alone do |
| not disqualify dispatch if |
| main body is above minimums.|
| |
| PROB40 / BECMG International / Military - PROB40 and BECMG are NOT |
| (Becoming) codes. used in domestic FAA TAFs. |
| - Used extensively in ICAO |
| TAFs across Europe and Asia.|
+-----------------------------------------------------------------------------+
[!IMPORTANT] FAA Domestic TAF Policy on PROB40 and BECMG: In domestic United States NWS TAFs, the
PROB40group is never used; if the probability of a phenomenon reaches 40% or greater, it must be forecast as a prevailing condition or within aTEMPOorFMgroup. Furthermore,BECMG(Becoming) is not authorized in standard domestic FAA TAFs (except for military aerodromes), ensuring unambiguous, discrete transition times for commercial air carrier dispatch.
6. Pilot Weather Reports (PIREP): Routine (UA) vs. Urgent (UUA)
Pilot reports provide ground meteorologists, dispatchers, and following flight crews with real-time verification of atmospheric conditions aloft. PIREPs are transmitted in standard coded format:
+-----------------------------------------------------------------------------+
| PIREP CODING ELEMENTS MATRIX |
| |
| Field Code Element Name Example Encoding |
| ----------------------------------------------------------------------- |
| /OV Location /OV JFK 120025 (JFK VOR 120° at 25NM)|
| /TM Time (UTC) /TM 1942 |
| /FL Flight Level / Altitude /FL330 (or /FL020 for 2,000 ft MSL) |
| /TP Type Aircraft /TP B77W (Boeing 777-300ER) |
| /SK Sky Cover /SK OVC012-TOP085 / BKN180-TOP240 |
| /WX Weather / Visibility /WX FV02SM +RA FG |
| /TA Air Temperature (°C) /TA -48 |
| /WV Wind Velocity /WV 270110KT |
| /TB Turbulence /TB SEV CAT FL310-350 |
| /IC Icing /IC SEV CLR 040-080 |
| /RM Remarks /RM LLWS +/- 18KT ON FINAL RWY 04R |
+-----------------------------------------------------------------------------+
Mandatory Urgent PIREP (UUA) Reporting Triggers
A PIREP must be classified and immediately broadcast as Urgent (UUA) when any of the following extreme atmospheric hazards are reported:
- Severe or Extreme Turbulence (including Clear Air Turbulence [CAT]).
- Severe Icing (ice accumulation rate exceeds deicing/anti-icing capability; immediate diversion required).
- Hail of any size (or $\ge 3/4$ inch in diameter).
- Volcanic Ash Clouds (airframe abrasion, engine flameout hazard).
- Low-Level Wind Shear (LLWS) with airspeed fluctuations of 10 knots or greater within 2,000 feet AGL.
- Tornadoes, Funnel Clouds, or Waterspouts.
- Any other weather phenomenon deemed by the PIC or ATC to present an immediate hazard to flight safety.
+-----------------------------------------------------------------------------+
| TURBULENCE & ICING CLASSIFICATION MATRIX |
| |
| Classification Operational Definition & Airframe Impact |
| ----------------------------------------------------------------------- |
| [TURBULENCE] |
| Light Slight erratic changes in altitude/attitude. Unsecured |
| objects displace slightly. Walking effortless. |
| Moderate Rapid bumps/jolts. Definite strain against seatbelts. |
| Unsecured objects dislodged. Walking difficult. |
| Severe Large, abrupt changes in altitude/attitude. Aircraft |
| temporarily out of control. Occupants forced violent- |
| ly against seatbelts. Unsecured objects tossed about. |
| Extreme Aircraft violently tossed, practically impossible to |
| control. Structural damage possible. Immediate declare.|
| Chop vs. Turb Chop = rapid, rhythmic bumpiness without altitude/ |
| attitude variations. Turb = erratic structural motion. |
| |
| [ICING] |
| Trace Ice becomes perceptible; rate of accumulation slightly |
| greater than rate of sublimation. No hazard. |
| Light Accumulation rate may create hazard if flight prolonged|
| (> 1 hour). Occasional deicing equipment cycles needed.|
| Moderate Accumulation rate requires continuous/frequent deicing.|
| Potentially hazardous; diversion necessary if failed. |
| Severe Accumulation exceeds capability of anti-ice/deicing |
| equipment. Ice builds on unprotected surfaces. |
| MANDATORY IMMEDIATE EMERGENCY DIVERSION. |
+-----------------------------------------------------------------------------+
Loading diagram...
Test Your Knowledge
A transport pilot reads the following remark in a METAR: 'SLP142 T00441011'. What is the exact sea level pressure, ambient temperature, and dewpoint?
A
B
C
D
Test Your Knowledge
Which of the following conditions mandates the immediate filing of an Urgent Pilot Weather Report (UUA) rather than a Routine PIREP (UA)?
A
B
C
D
Test Your Knowledge
In a domestic US National Weather Service Terminal Aerodrome Forecast (TAF), what does the TEMPO group specify regarding duration and applicability?
A
B
C
D