Drizzle consists of very fine, closely spaced water droplets with diameters less than 0.5 mm — significantly smaller than raindrops. It falls slowly and uniformly from low stratus or stratocumulus clouds, creating a persistent dampness rather than measurable heavy rainfall. Despite its gentle appearance, prolonged drizzle can saturate surfaces, reduce visibility to below 1 km, and make roads treacherously slippery.
Drizzle forms through the collision-coalescence process in clouds that are not deep enough or vigorous enough to grow larger raindrops. The cloud droplets need to collide and merge many thousands of times to reach drizzle size. Drizzle is especially common in maritime climates — the Atlantic coasts of Europe (Galicia, Brittany, Ireland, Scotland) and the Pacific Northwest of North America are famous for frequent drizzle. In Spanish, the word calabobos (fool-wetter) perfectly captures its deceptive nature.
In meteorological observations, drizzle is distinguished from rain by drop size and precipitation rate. Automated weather stations detect it using the impact size distribution of drops on optical sensors. For aviation, drizzle combined with temperatures near or below 0 °C creates a significant icing hazard — supercooled drizzle drops freeze on contact with aircraft surfaces. Drizzle is coded differently from rain on METAR reports and SYNOP observations, using the WMO codes 51–55 depending on intensity.