Learn how to read a METAR report for essential aviation weather data. Decode wind, visibility, clouds, and more with this comprehensive step-by-step guide.
Introduction
Aviation Routine Weather Reports, known as METARs, provide vital weather information for pilots and aviation enthusiasts. At first glance, these reports may seem like a confusing string of letters and numbers, but they contain critical data about flying conditions, including wind, visibility, clouds, and more. Pilots rely on METARs to assess current weather and make informed decisions about flight safety.
This guide will demystify METAR reports, showing you how to decode their format and interpret the information effectively. Whether you’re a student pilot, weather enthusiast, or professional aviator, understanding METARs is an essential skill. From report type and wind conditions to cloud coverage and additional remarks, we’ll break down each section of a METAR and explain how to read it like a pro.
Part 1: Finding the Report Type and Origin
Step 1: Obtain a METAR Report
METAR reports are available online through aviation weather services or directly from airport aviation centers. For example, the U.S. Aviation Weather Center provides METARs for various locations, which are updated hourly. Simply choose a location and time frame to access current or past reports.
Step 2: Identify the Report Type
The first code in the report specifies the type of report:
- METAR: Routine hourly weather report.
- SPECI: Special, unscheduled report issued for significant weather events like thunderstorms or low visibility.
- TAF: Terminal Aerodrome Forecast, used for predicting weather over a broader timeframe.
Step 3: Locate the Station Identifier
The station identifier follows the report type. It consists of a four-letter code assigned by the World Meteorological Organization (WMO):
- KAFF: U.S. Air Force Academy in Colorado (K = U.S.).
- EGLL: London Heathrow Airport (E = UK).
- RJAA: Tokyo Narita Airport (R = Japan).
Step 4: Decode the Date and Time
The six-digit code after the station identifier shows the date and time in Zulu time (UTC):
- Example: 212355Z
- 21: Day of the month.
- 2355: Time in Zulu (23:55 UTC).
This format excludes the month and year, so always check the context.
Step 5: Check for Modifiers
Modifiers provide additional information about the report’s origin:
- AUTO: Generated by an automated weather station.
- COR: A corrected report by a human observer.
Part 2: Determining Wind and Visibility Factors
Step 1: Interpret Wind Direction and Speed
The next section describes wind conditions:
- Example: VRB05KT
- VRB: Variable wind direction.
- 05KT: Wind speed of 5 knots.
Other codes:
- 180V260: Wind direction varies between 180° and 260°.
- G26KT: Gusts of 26 knots.
Step 2: Evaluate Visibility
Visibility is listed as a numerical value followed by units:
- 15SM: Visibility of 15 statute miles (used in the U.S.).
- 1400: Visibility of 1,400 meters (used internationally).
Fractions may also appear (e.g., 1 1/2SM for 1.5 miles).
Step 3: Assess Runway Visibility
Runway-specific visibility begins with R:
- Example: R36L/2400FT
- R36L: Runway 36 Left.
- 2400FT: Visibility of 2,400 feet.
Part 3: Obtaining Weather and Cloud Information
Step 1: Decode Present Weather Conditions
Weather conditions are represented by two-letter abbreviations, which may include intensity and descriptors. Examples include:
- -SHRA: Light rain showers.
- +TSRA: Heavy thunderstorms with rain.
- FG: Fog.
- HZ: Haze.
- VC: “In the vicinity” (near the station).
Step 2: Analyze Cloud Coverage
Sky conditions start with three-letter codes followed by altitude:
- SKC: Sky clear (manual reports).
- CLR: Clear below 12,000 feet (automated reports).
- FEW040: Few clouds at 4,000 feet.
- BKN220: Broken clouds at 22,000 feet.
- OVC: Overcast (total sky coverage).
Step 3: Check Cloud Height
The altitude of cloud bases is given in hundreds of feet:
- Example: SCT060: Scattered clouds at 6,000 feet.
- BKN220TCU: Towering cumulus clouds at 22,000 feet.
- VV003: Vertical visibility up to 300 feet.
Step 4: Read Temperature and Dew Point
Temperature and dew point are separated by a slash:
- Example: 15/M01
- 15: Temperature is 15°C.
- M01: Dew point is -1°C.
Step 5: Review the Altimeter Setting
Altimeter settings start with A for “altimeter,” followed by four digits:
- Example: A2957
- Atmospheric pressure of 29.57 inches of Mercury (Hg).
- International reports may use Q1030 for 1,030 hectopascals.
Step 6: Look for Additional Remarks
Remarks provide extra details, often using unique codes:
- ACSL DSNT SE-S: Altocumulus standing lenticular clouds in the distant southeast.
- SLP960: Sea level pressure of 996.0 millibars.
- 60001 55000: Automated maintenance codes.
Practice Example: Decoding a METAR Report
Sample METAR:
METAR KAFF 212355Z AUTO 18015KT 10SM -SHRA BKN060 BKN100 OVC220 15/M01 A2957 RMK AO2
Decoded:
- METAR: Routine report.
- KAFF: U.S. Air Force Academy station.
- 212355Z: Issued on the 21st at 23:55 Zulu time.
- AUTO: Generated automatically.
- 18015KT: Winds from 180° at 15 knots.
- 10SM: Visibility of 10 statute miles.
- -SHRA: Light rain showers.
- BKN060: Broken clouds at 6,000 feet.
- BKN100: Broken clouds at 10,000 feet.
- OVC220: Overcast clouds at 22,000 feet.
- 15/M01: Temperature is 15°C; dew point is -1°C.
- A2957: Altimeter set to 29.57 inches of Mercury.
- RMK AO2: Automated observation with a precipitation sensor.
Tips for Decoding METARs
- Use Charts for Reference:
Charts of abbreviations simplify decoding (e.g., NOAA METAR Guide). - Practice Regularly:
Familiarity comes with practice. Start with basic METARs and work up to more complex ones. - Understand Context:
Cross-reference METARs with other weather reports (like TAFs) for a comprehensive view.
Conclusion
Reading METAR reports is an essential skill for aviators, providing crucial weather information for flight planning and safety. By breaking down each section of the report—type, wind, visibility, clouds, and remarks—you can confidently interpret even the most complex METARs. Practice regularly, and you’ll soon decode aviation weather reports with ease, ensuring safer skies for every flight.
