Ground school · Lesson 4 of 8
Decoding METARs and TAFs
Area III · Weather · 4 min read
ACS UA.III.A · AC 00-45H
Aviation weather reports look like line noise until someone shows you the pattern; then they're free points. Two formats matter:
- METAR - METeorological Aerodrome Report. Ends in R = Report: current, observed weather. Issued hourly, valid for the hour. Your just-before-flight check.
- TAF - Terminal Aerodrome Forecast. Ends in F = Forecast: predicted weather. Issued four times daily at 0000Z, 0600Z, 1200Z, 1800Z, valid 24–30 hours. Your planning-tomorrow's-job check.
- SPECI - an unscheduled METAR, issued the moment weather changes enough to matter to aviation safety. Routine report on the clock, special report when something breaks the routine.
- PIREP - pilot report from the air (turbulence, icing, cloud tops). Background knowledge only.
Both METAR and TAF describe conditions within about 5 statute miles of the station. Get them at aviationweather.gov.
Universal conventions (these ARE the exam)
- Wind direction is where the wind is coming FROM, in degrees TRUE north. (Runway numbers and your compass are MAGNETIC - reports are true.)
- Speeds in knots (KT), not mph.
- Temperatures in Celsius. An answer choice in Fahrenheit is automatically wrong.
- All times are Zulu (UTC), marked Z. Zulu never changes and has no daylight saving. Later time groups inside a report drop the Z - they're still Zulu.
- Cloud heights: add two zeros, read as AGL. These are ground-based stations, so bases reference the ground, not sea level.
METAR, field by field
✋ Try it
Tap each token to decode it, then call it: legal to launch under §107.51?
Three real-world METARs: decode every token, then make the go / no-go call yourself.
METAR KATL 121755Z 18015G25KT 10SM FEW020 BKN250 18/12 A2992 RMK AO2 SLP110
| Token | Meaning |
|---|---|
METAR | Report type (could be SPECI). |
KATL | ICAO station. Leading K = contiguous US (KJFK, KLAX). |
121755Z | 12th day of the month, 17:55 Zulu. |
18015G25KT | Wind FROM 180° true (south) at 15 knots, Gusting 25. |
10SM | Visibility 10 statute miles. |
FEW020 | Few clouds, base 2,000 ft AGL (add two zeros). |
BKN250 | Broken layer at 25,000 ft. Multiple layers get listed low-to-high. |
18/12 | Temperature 18°C, dew point 12°C. |
A2992 | Altimeter 29.92 inches of mercury (standard sea-level pressure). |
RMK ... | Remarks. |
Cloud coverage codes: SKC/CLR clear, FEW 1–2 oktas, SCT scattered (3–4), BKN broken (5–7), OVC overcast (8). BKN and OVC are "ceilings."
Weather modifiers show up when visibility drops: 1SM -DZ BR = one mile in light drizzle and mist. Minus = light intensity, plus = heavy. Common codes: RA rain, DZ drizzle, SN snow, BR mist, FG fog, TS thunderstorm, SH showers.
Remarks worth recognizing: AO2 = automated station that can tell rain from snow; PK WND = peak wind since last report; RAB45 = rain began at :45; SLP = sea-level pressure; T-group = temp/dew point to tenths.
The remote-pilot payoff: when temperature and dew point converge, the air is saturating - fog and mist are next, and your 3 SM legal visibility is about to disappear. 18/17 at dusk means don't count on flying at dawn.
✈ Quick check
FEW020 in a METAR puts the cloud bases at…
TAF, field by field
TAF KJFK 121130Z 1212/1318 18012KT P6SM BKN040
FM121600 20015G25KT| Token | Meaning |
|---|---|
TAF | Report type - first token, top left. |
KJFK | Airport the forecast covers. |
121130Z | Issued the 12th at 11:30 Zulu. |
1212/1318 | Valid period, DDHH/DDHH: from the 12th at 1200Z through the 13th at 1800Z. Day and hour - not hours and minutes. |
18012KT | Wind from 180° at 12 kt. |
P6SM | P = plus = greater than: visibility better than 6 statute miles. |
BKN040 | Broken at 4,000 AGL. |
FM121600 | FM = "from": from the 12th at 1600Z, conditions change to the line that follows. |
Other change markers you may see: TEMPO (temporary fluctuations), BECMG (gradual becoming), PROB30 (30% probability). FM is the one the exam leans on.
✈ Quick check
18015G25KT. The wind is blowing…
How to practice
Read the code out loud the way it's spoken: "wind from one-eight-zero at one-five, gusting two-five." If you can say it, you can decode it - and you'll also understand the same information when an ATIS broadcast reads it to you. Pull real METARs from aviationweather.gov for airports near you and decode them until it's boring.
Traps to drill
- METAR = now, TAF = forecast (R = report, F = forecast).
- TAF issue schedule (0000/0600/1200/1800Z) and 24–30-hour validity.
- Wind FROM, degrees TRUE, knots.
- Celsius only. AGL cloud bases, add two zeros.
- P6SM = greater than 6 SM.
- Times without a Z are still Zulu.
- Validity
1212/1318is day+hour on both sides. - Temp/dew-point convergence = fog incoming = 3 SM at risk.
Done reading?
The read only sticks once you use it. Drill Area III while it is fresh.