Definition
In a METAR weather report, FU is the contraction used to indicate smoke as an obscuration to visibility. It denotes suspended combustion particles in the air — typically from wildfires, agricultural burning, or industrial sources — that reduce visibility at or near the reporting station.
Plain English
FU on a weather report means there is smoke in the air at the airport, and that smoke is reducing how far pilots can see.
Context Anchor
Seen in the weather portion of a METAR when smoke is affecting the airport area.
Derivation
The contraction FU comes from the French word 'fumée,' meaning smoke. Many METAR weather codes are based on French because the format was standardized internationally, and French was a working language of early aviation meteorology. Knowing this helps because FU has no obvious connection to the English word 'smoke' — the link only makes sense once you see the French root.
Why Pilots Care
Smoke reduces visibility and may signal nearby fires that affect takeoff, landing, or route choices.
Intuition Check
Do not read FU as an English abbreviation. In METARs, FU specifically means smoke in the air, not fuel, fumes, or fog.
Example Sentence 1
The METAR for KRDD reported FU with visibility down to three miles, so the pilot delayed departure until conditions improved.
Example Sentence 2
With FU reported at the destination, the crew reviewed alternate airports before departure.