Definition
Liquid water drops, larger than cloud droplets but smaller than ordinary raindrops, that exist in liquid form at temperatures below freezing (0°C). On contact with an aircraft surface they freeze rapidly, producing a particularly hazardous form of structural icing that often extends well aft of the protected leading edges.
Plain English
Tiny drops of water that are still liquid even though they are colder than freezing. When they hit an aircraft, they turn to ice almost instantly — and because they are bigger than normal cloud droplets, they spread back over more of the wing before freezing.
Context Anchor
Pilots encounter this term in icing weather discussions, forecasts, pilot reports, and training about flight near freezing drizzle or cold visible moisture.
Derivation
‘Supercooled’ means cooled below the normal freezing point while still remaining liquid. Pure water can stay liquid down to roughly −40°C if it has nothing to freeze around. ‘Drizzle drops’ refers to drop size — larger than cloud droplets (typically 50–500 microns) but smaller than full raindrops. Knowing the size matters: bigger drops carry more water and freeze further back along the wing.
Why Pilots Care
These drops can cause rapid clear-ice buildup that changes wing shape, reduces lift, and increases drag, creating an immediate safety hazard.
Grounding Statement
Picture flying through a cloud where the water has not yet frozen but desperately wants to — the moment a drop touches your wing, it freezes, and the larger drops spread back further before they do.
Intuition Check
Do not assume “supercooled” means extra cold ice. Here it means liquid water that is below freezing but has not frozen yet. Do not assume “drizzle” is harmless. In below-freezing air, drizzle-sized drops can create serious aircraft icing.
Example Sentence 1
The forecast warned of supercooled drizzle drops below 6,000 feet, so the crew elected to delay departure until conditions improved.
Example Sentence 2
The forecast called for supercooled drizzle drops below the cloud tops, so the crew activated the de-icing boots before descent.