Definition
A rotating, cone-shaped column of cloud extending downward from the base of a cumulonimbus or strong cumulus cloud, with associated violently rotating winds that have not reached the ground. If the rotating column touches the surface, it is reclassified as a tornado over land or a waterspout over water. In a METAR, FC is reported in the present weather group to indicate this hazardous phenomenon.
Plain English
A spinning, funnel-shaped cloud hanging from a thunderstorm. The winds inside it are violent, but the funnel hasn't reached the ground yet. If it touches down, it becomes a tornado.
Context Anchor
Seen in the present-weather section of a METAR when hazardous rotating cloud activity is reported.
Derivation
"Funnel" comes from the Latin infundibulum, meaning a cone-shaped vessel for pouring liquid. The cloud is named for its shape — wide at the top where it meets the parent cloud, narrowing downward toward the ground.
Why Pilots Care
Indicates strong rotating winds and potential tornado formation; pilots must avoid the area due to severe turbulence and wind shear risks.
Grounding Statement
Picture a dark cloud base with a rotating cone hanging down from it; that is the kind of cloud FC is warning about.
Intuition Check
Do not read FC as just an unusual-looking cloud. In a METAR, FC points to rotating severe-weather activity that can become or already be a tornado or waterspout.
Example Sentence 1
The METAR included FC in the present weather, so the crew diverted well clear of the storm cell.
Example Sentence 2
After the funnel cloud was reported, the tower suspended all departures until the storm passed.