A cold air funnel is a rotating column of air that descends from the base of a cloud. It often sparks public concern because of its visual similarity to a tornado. However, it is fundamentally different from the violent tornadoes associated with severe thunderstorms. The presence of a cold air funnel signals a particular type of atmospheric instability, which is far removed from the powerful systems that generate destructive tornadoes.
What Defines a Cold Air Funnel
A cold air funnel is a vortex that does not form within the powerful, rotating updraft of a supercell thunderstorm. Visually, the funnel is typically narrow and rope-like, extending downward from the base of a cumulus or stratocumulus cloud. It is a form of funnel cloud, defined as a rotating condensation funnel that does not reach the ground surface.
The visible funnel is composed of condensed water droplets, which become visible as the rotating air column causes a drop in air pressure and temperature. A cold air funnel is defined by remaining aloft. If the vortex briefly touches the ground, it is classified as a weak tornado, often called a cold air tornado or landspout, but this is rare.
Atmospheric Conditions Required for Formation
The meteorological environment necessary for a cold air funnel involves cold air high in the atmosphere combined with relatively warmer air near the surface. These funnels often develop in the wake of a cold front, within a cool air mass behind a low-pressure system. This setup creates a high lapse rate, meaning the air temperature drops rapidly with increasing height, leading to atmospheric instability.
The funnels are associated with a “cold core low,” a low-pressure system where the coldest air is located aloft, typically between 7,000 and 15,000 feet. This combination of warm surface air and very cold air at altitude helps trigger shallow, non-severe showers or towering cumulus clouds. Rotation begins when weak vertical wind shear interacts with updrafts beneath these clouds. The rising air then tightens and intensifies the rotation through vortex stretching, creating the visible funnel.
Key Differences from a Tornado
Classic tornadoes emerge from powerful supercell thunderstorms that feature deep, organized convection and intense rotation known as a mesocyclone. Cold air funnels, conversely, form from much weaker, non-severe showers or small thunderstorms that lack a strong, organized updraft.
Cold air funnels rarely produce damaging winds if they touch down, typically resulting in an EF0 rating on the Enhanced Fujita Scale, with winds generally up to 85 miles per hour. Classic tornadoes can reach significantly higher intensities, causing widespread destruction. Due to their weak, short-lived nature, the National Weather Service often issues only a Special Weather Statement for cold air funnels, rather than the Tornado Warning associated with severe, supercell-driven tornadoes.