METAR & TAF Decoding: Weather Minimums for Part 107 Operations

Understanding aviation weather reports is critical for passing the FAA Part 107 exam and conducting safe drone operations. As a remote pilot, you must be able to decode METAR (Meteorological Aerodrome Report) and TAF (Terminal Aerodrome Forecast) reports to determine if weather conditions meet the regulatory minimums for legal flight.

This comprehensive guide will teach you everything you need to know about weather reporting for the Part 107 exam, including how to read coded weather reports, understand visibility and cloud clearance requirements, and make informed go/no-go decisions.

What is a METAR Report?

A METAR (Meteorological Aerodrome Report) is a standardized observation of current weather conditions at an airport. METARs are issued hourly and provide real-time data that pilots use to assess whether conditions are safe for flight. SPECI reports are special unscheduled METARs issued when significant weather changes occur.

The format is standardized by the International Civil Aviation Organization (ICAO), though the United States uses statute miles for visibility, feet for altitude, and inches of mercury for altimeter settings (most other countries use metric).

METAR Format Breakdown

Let's decode a sample METAR step by step:

Wind Information Decoding

Wind reports are critical for drone operations. Here's how to read different wind scenarios:

• 26008KT - Wind from 260° at 8 knots (steady wind)
• 26008G15KT - Wind from 260° at 8 knots, gusting to 15 knots (G indicates gusts)
• 27012KT 240V300 - Wind from 270° at 12 knots, variable between 240° and 300° (when variation is 60° or more)
• 00000KT - Calm winds (less than 3 knots)
• VRB03KT - Variable direction at 3 knots (when wind speed is 6 knots or less)

Visibility Reporting

Visibility is crucial for Part 107 compliance. In the United States, visibility in METAR is reported in statute miles:

• 10SM - 10 statute miles visibility (excellent conditions)
• 3SM - 3 statute miles (minimum for Part 107)
• 1/2SM - One-half statute mile (below Part 107 minimums, no flight allowed)
• P6SM - Greater than 6 statute miles
• M1/4SM - Less than one-quarter statute mile (M = "minus" or less than)

Weather Phenomena Codes

METARs include codes for current weather conditions. Understanding these is essential for the exam:

Intensity Prefixes:

• - Light (e.g., -RA = light rain)
• (no prefix) Moderate (e.g., RA = moderate rain)
• + Heavy (e.g., +RA = heavy rain)

Cloud Cover Reporting

Cloud information is essential for maintaining the required 500 feet below and 2,000 feet horizontal clearance:

Cloud Height Examples:

• FEW008 - Few clouds at 800 feet AGL
• SCT025 - Scattered clouds at 2,500 feet AGL
• BKN012 - Broken layer at 1,200 feet (this is the ceiling)
• OVC005 - Overcast at 500 feet (very low ceiling)

What is a TAF Forecast?

A TAF (Terminal Aerodrome Forecast) provides weather forecasts for a 24 to 30-hour period at specific airports. Unlike METAR which reports current conditions, TAF predicts future weather trends, helping you plan drone operations in advance.

TAFs are typically issued four times daily (every 6 hours) and are updated sooner if significant weather changes are expected.

TAF Format Breakdown

Let's decode a sample TAF:

TAF Change Indicators

TAF forecasts use specific terms to indicate how weather conditions will change:

• FM (FROM) - Indicates a rapid, significant change expected at the specified time. All conditions after FM replace previous conditions entirely.
• TEMPO (TEMPORARY) - Temporary fluctuations lasting less than 1 hour at a time, occurring during the specified period. Conditions will fluctuate back and forth.
• BECMG (BECOMING) - Gradual change expected over a period (usually 1-2 hours). Final conditions will prevail after the change.
• PROB (PROBABILITY) - Indicates probability of occurrence (PROB30 = 30% chance, PROB40 = 40% chance). Usually combined with TEMPO.

Reading Our Sample TAF

Let's interpret the complete forecast:

1. 1218/1324 09008KT P6SM SCT250 - From 18:00Z on the 12th through 24:00Z on the 13th: Wind from 090° at 8 knots, visibility greater than 6 statute miles, scattered clouds at 25,000 feet. Excellent VFR conditions, good for Part 107.
2. FM122100 12012KT P6SM BKN100 - Starting at 21:00Z on the 12th: Wind shifts to 120° at 12 knots, visibility still >6SM, but now broken clouds at 10,000 feet. Still excellent for Part 107 operations.
3. FM130200 14015G25KT 4SM -SHRA BKN030 OVC050 - Starting at 02:00Z on the 13th: Wind from 140° at 15 knots gusting to 25 knots, visibility reduced to 4 statute miles in light rain showers, broken layer at 3,000 feet, overcast at 5,000 feet. Part 107 legal (>3SM visibility, >500 ft below 3,000 ft ceiling) but marginal conditions.
4. TEMPO 1302/1306 2SM TSRA BKN015CB - Temporary conditions between 02:00Z and 06:00Z on the 13th: Visibility drops to 2 statute miles in thunderstorms with rain, broken cumulonimbus clouds at 1,500 feet. Below Part 107 minimums - DO NOT FLY during these temporary conditions.

Practical Application: Can You Fly?

Let's practice with real-world scenarios you'll face on the Part 107 exam:

Scenario 1: Morning Flight Decision

Analysis:

• Visibility: 5 statute miles (✓ meets 3SM minimum)
• Cloud clearance: Scattered at 4,000 ft, broken at 10,000 ft. Ceiling is at 10,000 ft. Can fly up to 9,500 ft to maintain 500 ft below (✓ legal, though altitude limit is normally 400 ft AGL anyway)
• Wind: 270° at 15 knots gusting to 25 knots (within speed limits but check sUAS capabilities)

Decision: LEGAL TO FLY from a Part 107 regulatory standpoint, but assess wind conditions against your drone's capabilities.

Scenario 2: Foggy Conditions

Analysis:

• Visibility: 2 statute miles in mist (✗ below 3SM minimum)
• Cloud clearance: Overcast at 300 feet (extremely low ceiling)

Decision: NOT LEGAL TO FLY without a weather waiver under § 107.51. Visibility is below the 3-statute-mile requirement.

Scenario 3: Using TAF for Planning

Question: You want to fly at 20:00Z on the 15th. What are the forecast conditions?

Analysis: Look for the period covering 20:00Z (2000Z) on the 15th:

• FM151800 covers 18:00Z onwards: 220° at 15G28KT, visibility >6SM, scattered at 5,000 ft, broken at 10,000 ft
• These conditions continue until FM152300 (23:00Z)
• At 20:00Z: Visibility >6SM (✓), ceiling at 10,000 ft (✓), wind 15G28 knots

Decision: Forecast conditions are LEGAL for Part 107 operations at your planned flight time.

Where to Get Weather Information

As a remote pilot, you have multiple sources for obtaining weather information:

Official FAA Sources

• Aviation Weather Center (aviationweather.gov) - Free, official source for METAR/TAF
• 1800wxbrief.com - Leidos Flight Service for comprehensive briefings
• AWOS/ASOS - Automated weather reporting via phone or radio frequencies

Mobile Apps

• ForeFlight - Professional aviation weather (subscription)
• Garmin Pilot - Comprehensive weather and flight planning
• UAV Forecast - Drone-specific weather designed for sUAS operations
• B4UFLY - FAA's official app (includes basic weather)

Common Exam Questions on Weather

The FAA Part 107 exam frequently tests your ability to:

1. Identify whether conditions meet Part 107 minimums - Given a METAR, can you fly legally?
2. Determine ceiling heights - What is the ceiling in a given METAR?
3. Calculate cloud clearance - At what maximum altitude can you fly while maintaining required separation?
4. Decode wind information - What direction and speed is the wind?
5. Interpret TAF time periods - What are the forecast conditions at a specific time?
6. Recognize hazardous weather - Identify thunderstorms, low visibility, or other dangerous conditions

Practice Question 1

Question: What is the ceiling at Boston Logan?

Answer: 800 feet AGL. The broken layer at 008 (800 feet) constitutes the ceiling. Remember, the first broken (BKN) or overcast (OVC) layer defines the ceiling.

Practice Question 2

Question: Can you legally conduct Part 107 operations during the TEMPO period?

Answer: Yes, it is legal. During TEMPO (1520/1523), visibility is forecast at 4SM with light rain showers and broken clouds at 3,000 ft. Visibility of 4SM exceeds the 3SM minimum. The ceiling at 3,000 ft allows operations up to 2,500 ft while maintaining 500 ft below clouds. However, conditions are marginal, and a prudent pilot might wait for better weather.

Advanced Weather Considerations

Density Altitude

While not directly in METAR/TAF format, understanding the relationship between temperature and dewpoint helps assess atmospheric conditions. When temperature and dewpoint are close (within 2-3°C), fog or low clouds are likely to form. This is critical for morning or evening operations.

Altimeter Settings

The altimeter setting in a METAR tells you the current pressure. High pressure (above 30.00) indicates stable, clear weather. Low pressure (below 29.80) often means approaching weather systems with clouds and precipitation.

Wind Shear

Some TAFs include wind shear information (WS) for low-level operations. For example, WS020/35045KT means wind shear at 2,000 feet with winds from 350° at 45 knots above that level. This indicates rapidly changing wind conditions that can affect drone stability.

Weather Decision-Making for Remote Pilots

Beyond just meeting regulatory minimums, safe drone operations require good aeronautical decision-making:

1. Never fly in or near thunderstorms - Even if legally permissible, thunderstorms produce severe turbulence, wind shear, lightning, and rapidly changing conditions. If you see TSRA, TS, or CB in weather reports, DO NOT FLY.
2. Consider personal minimums above regulatory minimums - Just because 3SM visibility is legal doesn't mean it's wise. Many professional pilots set personal minimums at 5SM visibility and 1,000-foot ceilings for routine operations.
3. Account for forecast deterioration - If TAF shows conditions worsening during your planned operation window, plan accordingly or reschedule.
4. Check multiple sources - Don't rely on a single weather app. Cross-reference with official FAA sources.
5. When in doubt, don't fly - Weather-related accidents are often preventable. If conditions are marginal or you're uncertain, wait for better weather.

Exam Preparation Checklist

To master weather for the Part 107 exam, ensure you can:

• ✓ Recite from memory: 3SM visibility, 500 feet below clouds, 2,000 feet horizontal from clouds
• ✓ Identify station ID, date/time, wind, visibility, weather, clouds, temp/dewpoint, altimeter in any METAR
• ✓ Determine ceiling height from cloud reports
• ✓ Calculate maximum legal operating altitude given a ceiling
• ✓ Decode wind direction, speed, and gusts
• ✓ Interpret TAF valid periods and time groups (FM, TEMPO, BECMG)
• ✓ Recognize weather phenomena codes (RA, TSRA, FG, BR, etc.)
• ✓ Determine if given weather conditions meet Part 107 minimums
• ✓ Identify hazardous weather that prohibits flight

Additional Resources

• FAA-H-8083-25B - Pilot's Handbook of Aeronautical Knowledge (Chapter 12: Weather Theory; Chapter 13: Aviation Weather Services)
• FAA-AC-00-45H - Aviation Weather Services Advisory Circular
• AIM Chapter 7 - Safety of Flight (weather information)
• Aviationweather.gov - Free training modules on METAR/TAF interpretation

Conclusion

Mastering METAR and TAF interpretation is non-negotiable for Part 107 success. These coded reports provide the critical information you need to determine if conditions are safe and legal for flight. The exam will test your ability to quickly decode weather reports and apply Part 107 weather minimums.

Practice decoding real weather reports daily, memorize the 3SM/500 ft/2,000 ft requirements, and learn to recognize hazardous conditions. With consistent practice, reading aviation weather will become second nature, serving you well on exam day and throughout your career as a remote pilot.