Definition
In a METAR or TAF weather report, FU is the contraction used to indicate smoke as the present weather phenomenon, signifying suspended combustion particles in the air that reduce visibility.
Plain English
FU is the code that tells you smoke is in the air at the airport, usually thick enough to cut down how far you can see.
Context Anchor
Seen in coded airport weather reports, such as METARs, in the present-weather section.
Derivation
FU comes from the French word fumée, meaning smoke. The FAA and ICAO weather code system uses two-letter abbreviations drawn from various languages to keep each code unique; SM was already taken for statute miles, so the French root was used instead.
Why Pilots Care
Smoke reduces visibility and may require pilots to adjust routing or delay flights.
Intuition Check
FU does not mean fuel or fumes in a weather report. In this context, it specifically means smoke affecting the air.
Example Sentence 1
The METAR showed FU with visibility down to three miles, so the pilot expected hazy conditions on approach.
Example Sentence 2
FU was reported downwind of the wildfire, prompting an alternate route.