Freezing drizzle

Freezing drizzle is drizzle that freezes on contact with the ground or an object at or near the surface. Its METAR code is FZDZ.

Freezing drizzle is formed in low level stratus type clouds when vertical motion is weak. It consists of relatively small drops, light in nature. Freezing drizzle generally occurs when drizzle forms in an airmass at below freezing temperatures but warmer than -10 °C (14 °F). At such a temperature, the water droplets stay supercooled as there are few ice nuclei to change them to ice crystals (see freezing rain). In winter arctic conditions it can happen at even lower surface temperatures as the air is even cleaner.

When freezing drizzle accumulates on land it creates an icy layer of glaze. Freezing drizzle alone does not generally result in significant ice accumulations due to its light, low-intensity nature. However, even thin layers of slick ice deposited on roads as black ice can cause extremely hazardous conditions resulting in vehicle crashes.

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Wikipedia