Definition
In a METAR, FZ is a descriptor used in the present-weather group to indicate that liquid precipitation is freezing on contact with the ground or with exposed surfaces, producing a coating of ice. It is most commonly seen paired with RA (rain) or DZ (drizzle), as in FZRA or FZDZ, and indicates that the air near the surface is below 0°C even though the precipitation itself is falling as liquid.
Plain English
FZ means the rain or drizzle in the report is freezing as soon as it lands, coating runways, aircraft, and other surfaces with ice.
Context Anchor
Seen in METAR present-weather groups, such as reports of freezing rain, freezing drizzle, or freezing fog.
Derivation
From the English word freeze, meaning to turn from liquid to solid through cold. In METAR shorthand it is reduced to the two-letter code FZ to keep reports compact.
Why Pilots Care
Freezing precipitation causes rapid ice buildup on wings and control surfaces, sharply reducing lift and increasing the risk of stall or loss of control.
Grounding Statement
A droplet can still be liquid even when it is colder than 0°C, and it may freeze only when it touches something.
Intuition Check
Do not read FZ as simply “the outside air is below freezing.” In a METAR, FZ means the reported water droplets can freeze on contact.
Example Sentence 1
The METAR showed FZRA, so the pilot cancelled the departure rather than risk ice forming on the wings during taxi.
Example Sentence 2
Before departure the crew scanned the METAR for any FZ prefix to decide whether de-icing was required.