Definition
A narrow, funnel-shaped cloud that extends from the base of a small cumulus or shower cloud in a cold, unstable air mass aloft. Cold air funnels form well away from thunderstorms, are usually weak, and only rarely reach the ground as tornadoes.
Plain English
A small, funnel-shaped cloud that hangs down from the bottom of a regular shower cloud when the air high up is unusually cold. It looks like a tornado but is much weaker and almost never touches the ground.
Context Anchor
Seen in weather briefings, pilot reports, and visual weather decisions near showers, especially on cool days with cold air above the surface.
Derivation
Named for the conditions that produce it: a pool of cold air aloft sitting over warmer air below creates the instability that lets the funnel form. The word ‘funnel’ describes the tapered, cone-like shape.
Why Pilots Care
Signals possible localized gusts and turbulence that can affect low-altitude flight even when no thunderstorm is present.
Grounding Statement
Picture an ordinary rain shower on a cool, blustery day, and a small cone-shaped tail dangling from its base for a minute or two before vanishing — that is a cold air funnel.
Intuition Check
A cold air funnel is not just cold air shaped like a funnel. It is a rotating funnel cloud that forms in cold-air weather and can become dangerous if it reaches the surface.
Example Sentence 1
On the flight back, we spotted a cold air funnel hanging beneath a small shower cloud and altered course to give it room.
Example Sentence 2
Although a cold air funnel was visible five miles west, the pilot continued the approach with no surface winds reported.