What is the difference between a METAR and a TAF?

A METAR (Meteorological Aerodrome Report) is an observation of current surface weather conditions at a specific airport, typically issued every hour or as a special report when conditions change significantly. A TAF (Terminal Aerodrome Forecast) is a forecast of expected weather conditions, usually covering a 24- or 30-hour period within a 5-statute-mile radius of an airport. METARs tell you what the weather is right now, while TAFs tell you what forecasters expect it to become, making both essential tools for preflight planning as described in the FAA Aviation Weather Handbook.

How do you decode cloud layers in a METAR?

Cloud layers in a METAR are reported using three-letter descriptors followed by a height in hundreds of feet AGL: FEW (1–2 oktas), SCT for scattered (3–4 oktas), BKN for broken (5–7 oktas), and OVC for overcast (8 oktas). For example, BKN025 means a broken ceiling at 2,500 feet AGL. The ceiling is defined as the lowest broken or overcast layer, or a vertical visibility value, and is critical for determining VFR versus IFR conditions as outlined in the Pilot's Handbook of Aeronautical Knowledge.

Why is it important to understand METAR and TAF decoding for the FAA Private Pilot Airman Knowledge Test?

The FAA Private Pilot Airman Knowledge Test includes questions that require you to accurately read and interpret METAR and TAF reports to assess weather suitability for a proposed flight. Misreading coded weather data can lead to incorrect go/no-go decisions, making this a safety-critical skill beyond just test preparation. The FAA Airman Certification Standards for the Private Pilot certificate specifically require applicants to demonstrate the ability to obtain, read, and correctly interpret aeronautical weather reports and forecasts.

METAR and TAF Decoding for Preflight Weather Assessment

Every preflight begins with weather, and two documents sit at the center of that process: the METAR (Meteorological Aerodrome Report) and the TAF (Terminal Aerodrome Forecast). Together they give you a snapshot of current conditions at a specific airport and a look ahead at what conditions are expected to be. The FAA knowledge test routinely includes METAR and TAF decoding questions, and real-world pilots depend on accurate interpretation of these products every day. Understanding how to read them fluently — not just memorize a format — is one of the most transferable skills you will develop as a student pilot.

Both products are produced in a standardized international format established by the World Meteorological Organization (WMO) and adopted by the FAA. This means the same coding convention you learn for a U.S. airport applies almost everywhere in the world, making the investment in learning it especially worthwhile. The Aviation Weather Handbook (FAA-H-8083-28) provides the authoritative treatment of both products and is the primary source behind everything discussed here.

Understanding the METAR: A Snapshot of Current Conditions

A METAR is an hourly surface observation of conditions at an airport, typically issued at 55 minutes past the hour and valid at the top of the hour. Some stations issue a SPECI (Special Observation) between routine hours whenever conditions change significantly — for example, when visibility drops below three miles or the ceiling drops below 1,000 feet. METARs are generated by automated surface observing systems (ASOS/AWOS) or human observers, and the two types can look slightly different in practice.

A typical METAR looks like this:

METAR KORD 121755Z 27018KT 10SM FEW035 SCT080 BKN250 22/10 A2992 RMK AO2 SLP132

Here is what each element means, in sequence:

METAR — Report type. SPECI would indicate a special observation.
KORD — ICAO station identifier. U.S. stations begin with K; Alaska with PA; Hawaii with PH.
121755Z — Date and time. Day 12 of the month, 1755 UTC (Zulu). All aviation weather times are in UTC.
27018KT — Wind direction (270°, from the west) and speed (18 knots). A gust would appear as, for example, 27018G28KT. Variable wind less than 3 knots is coded VRB03KT. Wind direction is always reported as magnetic in U.S. METARs.
10SM — Prevailing visibility in statute miles. Values below 1/4 SM may read M1/4SM (M = less than).
FEW035 SCT080 BKN250 — Sky condition, in hundreds of feet AGL. FEW = 1-2 oktas (eighths); SCT (Scattered) = 3-4 oktas; BKN (Broken) = 5-7 oktas; OVC (Overcast) = 8 oktas. A ceiling is the lowest broken or overcast layer, or a vertical visibility figure. In this example, the ceiling is 25,000 feet — a severe clear day — but the BKN250 is what officially defines the ceiling.
22/10 — Temperature/dewpoint in degrees Celsius. The closer these numbers are, the higher the relative humidity and the greater the likelihood of fog or precipitation.
A2992 — Altimeter setting in inches of mercury. Setting this value in your Kollsman window causes the altimeter to display indicated altitude (height above mean sea level) — not pressure altitude. Pressure altitude is obtained only by setting 29.92 in Hg in the Kollsman window.
RMK AO2 SLP132 — Remarks. AO2 means the automated station has a precipitation discriminator (it can detect rain vs. snow). SLP132 means sea-level pressure is 1013.2 hPa. To decode SLP, take the three digits given and prepend either a 9 or a 10, whichever produces a value closest to 1000 hPa — so 132 becomes 1013.2 hPa (not 913.2), since 1013.2 is nearer to 1000 than 913.2 is.

Understanding the TAF: A Look at Expected Conditions

A TAF is a forecast, not an observation. It is issued four times daily (at 0000, 0600, 1200, and 1800 UTC) by National Weather Service aviation forecast offices and covers a 5 statute mile radius around the airport. Standard TAFs cover a 24-hour period; 30-hour TAFs are standard at major hub airports. Like METARs, TAFs use the same coding conventions for wind, visibility, and sky condition.

A sample TAF:

TAF KORD 121720Z 1218/1318 27015KT 9999 FEW040 TEMPO 1220/1224 27025G35KT 3SM TSRA BKN020CB FM130400 09008KT 5SM BR OVC010 BECMG 1308/1310 12010KT 9999 SCT030

TAF KORD 121720Z — Forecast type, station, and issuance time (day 12, 1720Z).
1218/1318 — Valid period: from day 12 at 1800Z through day 13 at 1800Z (24 hours).
27015KT 9999 FEW040 — Prevailing conditions for the period. Visibility 9999 means 10 km or more (essentially "greater than 6 SM" in U.S. usage).
TEMPO 1220/1224 — Temporary conditions expected during the stated hours, each lasting less than one hour at a time and occurring less than half of the period. Here: 27025G35KT winds, 3SM visibility in thunderstorms and rain, broken ceiling at 2,000 feet with cumulonimbus (CB).
FM130400 — "From" group. A rapid, permanent change beginning day 13 at 0400Z. All conditions reset to the values that follow (09008KT, 5SM in mist, OVC 1,000 feet).
BECMG 1308/1310 — Becoming. A gradual change expected to complete within the stated time window (0800-1000Z on day 13). After completion: 10-knot southeast wind, visibility 10+ SM, scattered at 3,000 feet.

Sky Condition and Ceiling: The VFR/IFR Bridge

One of the most tested concepts in weather decoding is how sky condition determines flight category. The FAA uses four categories:

VFR — Ceiling greater than 3,000 feet AGL and visibility greater than 5 SM.
MVFR (Marginal VFR) — Ceiling 1,000–3,000 feet AGL and/or visibility 3–5 SM.
IFR — Ceiling 500–999 feet AGL and/or visibility 1–3 SM.
LIFR (Low IFR) — Ceiling below 500 feet AGL and/or visibility below 1 SM.

A private pilot operating under VFR must stay clear of these conditions. Remember: the ceiling is always the lowest broken or overcast layer — a METAR showing BKN045 means a 4,500-foot ceiling, not the scattered layers below it. SKC (sky clear) and CLR (clear below 12,000 feet at automated stations) indicate no ceiling.

Why This Matters: The Go/No-Go Decision

Being able to decode a METAR or TAF quickly and correctly is not just an academic exercise. Under 14 CFR Part 91, pilots in command are responsible for obtaining a weather briefing before any flight. The METAR tells you what conditions exist right now; the TAF tells you what a trained meteorologist forecasts they will be. Used together, they let you identify whether your departure, en route, and destination conditions meet the minimums for your certificate and the airspace you plan to fly.

For example, if your destination TAF shows a TEMPO group with IFR ceilings and visibility during your estimated arrival window, you need to plan for an alternate or delay. If the TAF shows a BECMG group that won't complete until after your flight, you need to know whether interim conditions are acceptable. Missing these change groups — especially TEMPO — is one of the most common preflight planning errors.

Key Numbers and Rules

METARs are issued hourly; SPECIs are issued as conditions change significantly.
TAFs cover a 5 SM radius around the airport and are valid for 24 hours (30 hours at major hub locations).
Wind direction in METARs is in magnetic degrees; 00000KT means calm.
Visibility in U.S. METARs is in statute miles; TAFs may show meters internationally (9999 = 10+ km).
Cloud heights in both products are always AGL, not MSL.
A ceiling is the lowest BKN or OVC layer (or VV for vertical visibility in obscurations).
Temperature and dewpoint spread of 4°C or less suggests a high likelihood of fog or low clouds forming.
CB (cumulonimbus) or TCU (towering cumulus) in a sky group indicates significant convective activity and must be taken seriously — these are never routine.

Memory Aid

For TAF change groups, remember: