Plain English Meaning

Tiny drops of water in the air that are colder than freezing but are still liquid. The moment they touch your aircraft, they turn to ice.

Full Definition

Liquid water droplets that exist at temperatures below 0°C (32°F) without having frozen. These droplets remain liquid because they lack a surface or particle to freeze onto, but they freeze almost instantly on contact with an aircraft, producing structural icing.

Context Anchor

Seen in instrument weather and aircraft icing discussions, especially when flying in clouds or precipitation at temperatures near or below freezing.

Derivation

‘Subfreezing’ combines the Latin sub- (‘below’) with ‘freezing’ — literally ‘below the freezing point.’ The phrase highlights that the droplets are colder than 0°C even though they have not yet frozen.