What visible funnel forms when water vapor condenses in a tornado's low-pressure core?

The visible funnel that forms when water vapor condenses in a tornado’s low-pressure core is called a condensation funnel. Rapidly rotating air inside the vortex experiences lower pressure and expands, which cools it. If the air cools to its dew point, water vapor condenses into tiny droplets that become visible as a funnel-shaped cloud.

The condensation funnel is not the tornado itself. The tornado is the rotating column of air and wind; the funnel is only the visible cloud produced by condensation. A tornado can therefore exist without a fully visible funnel, particularly when humidity is low or precipitation and darkness obscure it.

A funnel cloud is often used as a near-synonym in general reporting, but meteorologists may distinguish a funnel cloud that remains above the surface from a tornado with a surface circulation. A gust front is an outflow boundary, an anvil cloud spreads from a storm’s top, and a shelf cloud forms along an advancing gust front.