Definition
The lowest altitude in the atmosphere at which the air temperature reaches 0°C (32°F). Above this altitude, temperatures are at or below freezing, creating conditions where water in clouds or precipitation can freeze on contact with the aircraft.
Plain English
The height above the ground where the air gets cold enough to freeze water. Below it, the air is warmer than freezing; above it, the air is at or below freezing.
Context Anchor
Seen in weather briefings, forecasts, and instrument flight planning, especially when clouds, rain, or snow may be present.
Derivation
“Freezing” comes from an old word meaning to turn into ice. “Level” means a height or line. Together, “freezing level” means the height in the air where the temperature reaches the freezing point.
Why Pilots Care
Aircraft icing can begin above this altitude, reducing lift and potentially leading to loss of control.
Grounding Statement
If you climb through a cloud and the temperature drops to 0°C, you have reached the freezing level for that layer of air.
Intuition Check
Do not assume the freezing level is always at the ground or that everything above it is automatically icy. It is the altitude where the air reaches freezing temperature; ice also needs moisture to form on the aircraft.
Example Sentence 1
The briefer reported a freezing level of 6,000 feet, so the pilot planned to cruise at 4,500 feet to stay below it while flying through the clouds.
Example Sentence 2
With the freezing level near the surface, the pilot elected to remain on the ground until conditions improved.