What Does FU Mean in a METAR?
FU means smoke. It stands for from French fumée - smoke.
FU in a real report
FU
That reads as smoke.
What it changes for you
Smoke behaves like haze that can change its mind. It is dry particulate, so it does not respond to temperature, but the source is a fire that moves and grows.
Two things make it worth more caution than haze:
- Density can change rapidly as the wind shifts relative to the fire
- Smoke layers can extend to high altitude, so climbing out of it is not always the option it is with a shallow haze layer
Where it shows up
Wildfire season in the western United States and Canada, and it travels a long
way. A field a thousand miles from any fire can report FU when the upper flow
brings the plume across. Check whether the visibility trend across several
stations is regional rather than local.
Related codes
Decode a report containing this code
Paste a METAR, TAF, PIREP or SIGMET into the WxDecoder decoder. Every group comes back in plain English. The raw code sits beside it, so you can check the decode rather than trust it.
Frequently asked questions
What does FU mean in a METAR?
Smoke. From the French fumee. It is reported when smoke restricts visibility, most often from wildfires, and it can persist for days over a wide area rather than clearing with the diurnal cycle.
Is smoke worse than haze for flying?
Often yes. Smoke can be much denser, can change quickly as the fire and wind change, and can extend to high altitude. It also carries a real risk of sudden deterioration that haze does not.