Definition
Any temperature below the freezing point of water — that is, below 0°C (32°F).
Plain English
Context Anchor
Seen in weather briefings, icing discussions, runway condition reports, and preflight decisions when cold weather and moisture may affect the flight.
Derivation
The prefix 'sub-' comes from Latin meaning 'below' or 'under.' So 'subfreezing' simply means 'below the freezing point.'
Why Pilots Care
Subfreezing temperatures signal possible aircraft icing that reduces lift, increases drag, and can block engine air intakes.
Grounding Statement
If the temperature is below 32 °F and moisture is present, a pilot should be thinking about possible ice or frost.
Intuition Check
Subfreezing temperature does not always mean ice is already visible. It means conditions are cold enough that ice or frost can form if moisture is present.
Example Sentence 1
The pilot delayed departure until the engine was pre-heated, since the aircraft had been parked overnight in subfreezing temperatures.
Example Sentence 2
Carburetor heat was applied in subfreezing temperatures even though the sky remained clear of clouds.