Definition
Drizzle composed of very small liquid water droplets, typically less than 0.5 millimeters in diameter, that fall to the surface in a supercooled (below-freezing) liquid state and freeze on contact with objects whose temperature is at or below 0°C. Reported as FZDZ in aviation weather products.
Plain English
Tiny liquid raindrops that are colder than freezing but still liquid in the air. The moment they touch the aircraft, the runway, or the ground, they turn into ice.
Context Anchor
Pilots encounter this term in weather reports, forecasts, and icing discussions, often shown as FZDZ, the weather-report code for freezing drizzle.
Derivation
‘Drizzle’ comes from the Old English ‘drysnian’, meaning to fall in fine drops. The droplets are too small to be called rain but too numerous to ignore. ‘Freezing’ here refers to what happens on impact, not what the droplets are doing while falling.
Why Pilots Care
Causes ice buildup on wings and surfaces, reducing lift and increasing drag even in light conditions.
Analogy
It is like a very fine spray that looks harmless in the air but instantly coats a cold railing with ice when it touches it.
Grounding Statement
The key point is that the drops are liquid while falling and become ice on contact with a cold surface.
Intuition Check
Do not picture ice pellets or snow falling from the sky. In freezing drizzle, the drops are liquid as they fall; the freezing happens when they hit something cold.
Example Sentence 1
The METAR reported FZDZ at the destination, so the pilot diverted rather than risk severe airframe icing on approach.
Example Sentence 2
Freezing drizzle can coat the wings with ice during approach even when rain is light.