Freezing Drizzle
Freezing drizzle (FZDZ) is precipitation consisting of very small water droplets (less than 0.5 mm diameter) that fall in liquid form but freeze on contact with surfaces at or below 0°C. It is reported in METARs using the code FZDZ and is one of the most hazardous forms of precipitation for aircraft operations.
Formation
Freezing drizzle forms when liquid droplets in low-level cloud or drizzle fall through a shallow layer of air that is just below freezing at the surface. Unlike freezing rain (which involves melting and refreezing), freezing drizzle droplets may remain supercooled throughout their fall from very low cloud bases.
Aviation Hazards
- Clear ice accretion on all exposed aircraft surfaces, including critical aerodynamic surfaces
- Can occur with very low cloud bases — little margin for error in VMC operations
- Hazard extends into the cloud layer where airborne icing is possible
- Ground icing on runways, taxiways, and aircraft parked outside
- Holdover time for de/anti-icing fluid is significantly reduced in FZDZ
FZDZ vs. FZRA
Both freezing drizzle and freezing rain (FZRA) deposit clear ice. FZRA drops are larger and generally deposit ice faster. FZDZ drops are smaller and may be harder to distinguish visually. Both require immediate attention — if you encounter either in flight, exit the area immediately.
On the TC Written Exam
Know FZDZ in METAR code, know how it forms, and understand the icing hazard. Distinguish it from FZRA by drop size (FZDZ < 0.5 mm, FZRA ≥ 0.5 mm).
Related Terms
See also: Freezing Rain, Icing, Aircraft Critical Surface Contamination.