How to use it
- Paste a METAR, SPECI or TAF into Weather report, or keep the sample that is already there.
- Read Flight category first. It gives VFR, MVFR, IFR or LIFR and the ceiling or visibility that decides it.
- Go through Decoded report. Each row is one group of the code, with the raw group in brackets.
- For a TAF, read each period block: the period's type and times come first. Use Download as CSV under the table to keep it.
How each part of the report is read
A report is read group by group, in the order the code uses. The first groups give the report type (METAR, SPECI or TAF), the station (a four-letter ICAO code such as LTFM) and the time in UTC: 101520Z is day 10 at 15:20 UTC.
Wind is a direction and a speed: 21007KT is 210 degrees at 7 knots. G gives the gust, a range such as 170V240 gives the directions the wind varies between, and VRB means a variable direction. The units are KT (knots), MPS (metres per second) or KMH (kilometres per hour).
Visibility is in metres (four digits, where 9999 means 10 km or more) or in statute miles (SM). CAVOK replaces the visibility, the clouds and the weather when conditions are good: no cloud below 5,000 ft, visibility 10 km or more and no significant weather.
Clouds are an amount, a height in hundreds of feet and an optional type. BKN015 is broken cloud at 1,500 ft. FEW and SCT are scattered cloud; BKN and OVC make the ceiling. VV is the vertical visibility into a sky that is hidden.
Temperature and dew point are in whole degrees Celsius, and M means minus: M01 is -1 degree. The pressure is Q and hectopascals (Q1021, the QNH) or A and inches of mercury, the altimeter setting: A2998 is 29.98 inHg, which the page converts with 1 inHg = 33.8638866667 hPa.
A TAF is read period by period. FM starts a new set of conditions at a given day and time, BECMG is a gradual change, TEMPO a temporary one and PROB30 or PROB40 a chance of the conditions.
- Weather groups use the FAA table of present weather in AIM 7-1-28: intensity (- light, no sign moderate, + heavy), VC (in the vicinity), descriptors and phenomena.
Flight category rules (AIM 7-1-7)
The category is the worse of two things: the ceiling and the visibility. The ceiling is the lowest broken (BKN) or overcast (OVC) layer, or the vertical visibility (VV) into an obscured sky. FEW and SCT layers are not ceilings.
Category = the worse of the ceiling category and the visibility category- LIFR (low IFR): ceiling less than 500 ft, and/or visibility less than 1 mile.
- IFR: ceiling 500 to less than 1,000 ft, and/or visibility 1 to less than 3 miles.
- MVFR (marginal VFR): ceiling 1,000 to 3,000 ft, and/or visibility 3 to 5 miles inclusive.
- VFR: ceiling greater than 3,000 ft and visibility greater than 5 miles. A sky that is clear is VFR.
- CAVOK is VFR. A visibility of 9999 (10 km or more) is above 5 miles.
What this decoder does not cover
- Not for flight planning or briefing: use the official briefing of your authority.
- It is not a replacement for an official briefing. It does not read aircraft limits, performance or airport procedures: use the aircraft's manual.
- Forecast products such as SIGMET, AIRMET, PIREP and NOTAM are not decoded.
- Remarks (RMK) are shown as they were sent, not decoded. A group the decoder does not know is never dropped: it is shown as not decoded.
- The weather names follow the FAA table in AIM 7-1-28. Code tables used in other countries can differ in small details.
Worked example: LTFM, day 10 at 15:20 UTC
The default report is METAR LTFM 101520Z 21007KT CAVOK 11/09 Q1021 NOSIG, with runway wind remarks after RMK. 21007KT is wind from 210 degrees at 7 knots.
CAVOK means the visibility is 10 km or more, there is no cloud below 5,000 ft and there is no significant weather, so the flight category is VFR. 11/09 is 11 °C and a dew point of 9 °C. Q1021 is a QNH of 1021 hPa, and NOSIG says no significant change is expected.
| Item | Value |
|---|---|
| Station | LTFM |
| Observation time | day 10, 15:20 UTC |
| Wind | 210 degrees, 7 kt (21007KT) |
| Visibility | CAVOK: no cloud below 5,000 ft, visibility 10 km or more, no significant weather |
| Temperature | 11 °C (11/09) |
| Dew point | 9 °C |
| Pressure | 1021 hPa (Q1021) |
| Flight category | VFR: CAVOK |
Frequently asked questions
What is the difference between a METAR and a TAF?
A METAR reports the weather that has been observed at an airport at one time. A TAF is a forecast for the airport over a period, usually 24 or 30 hours, split into periods that show how the conditions are expected to change.
Why does the flight category show LIFR when the clouds are high?
The category is the worse of the ceiling and the visibility. A visibility of 800 m is less than one statute mile, so it gives LIFR even when the clouds are high. The reason after the colon names the cause.
Do FEW and SCT clouds count as a ceiling?
No. The ceiling is the lowest broken (BKN) or overcast (OVC) layer, or the vertical visibility (VV). Scattered or few layers are not ceilings, so they do not lower the category on their own.
What does CAVOK mean?
CAVOK means the visibility is 10 km or more, there is no cloud below 5,000 ft and there is no significant weather. The decoder treats CAVOK as VFR, as the AIM does.
Why is a group marked not decoded?
The decoder knows the groups it was built for. Rather than drop a group it does not know, it shows the raw text marked as not decoded, so you can read it yourself or look it up in the code tables.
Can I use the decoder to plan a real flight?
No. It is for training and planning practice, not for real flight. Real flight decisions use the official weather briefing of your authority and the aircraft's manual.
Does the decoder send the report to a server?
No. The report is decoded in your browser. Nothing you paste is sent to us or stored by the page.
Sources
- FAA Aeronautical Information Manual, chapter 7, section 1 (AIM 7-1-7, 7-1-28, 7-1-29)
- Aviation Weather Center Data API (raw METAR and TAF text formats)
Figures and text last checked on Tuesday, November 10, 2026.