Freezing drizzle in the context of "METAR"

Drizzle is a light precipitation which consists of liquid water drops that are smaller than those of rain – generally smaller than 0.5 mm (0.02 in) in diameter. Drizzle is normally produced by low stratiform clouds and stratocumulus clouds. Precipitation rates from drizzle are on the order of a millimetre (0.04 in) per day or less at the ground. Owing to the small size of drizzle drops, under many circumstances drizzle largely evaporates before reaching the surface, and so may be undetected by observers on the ground. The METAR code for drizzle is DZ and for freezing drizzle is FZDZ.

Rime ice forms when supercooled water droplets freeze onto surfaces. In the atmosphere, there are three basic types of rime ice:

• Soft rime forms when supercooled water freezes under calm wind conditions. It is milky and crystalline, like sugar, and similar to hoar frost.
• Hard rime forms by rapid freezing of supercooled water under at least moderate wind conditions. The droplets freeze more or less individually, leaving air gaps.
• Clear ice forms by slow freezing of supercooled water. Clear ice is typically transparent and homogeneous. Its amorphous and dense structure makes it adhesive.

Soft and hard rime are less dense than clear ice and less adhesive, thus generally cause less damage. Glaze ice is similar in appearance to clear ice, however it is the result of a completely different process, occurring during freezing rain or drizzle.

Glaze or glaze ice, also called glazed frost or verglas, is a smooth, transparent and homogeneous ice coating occurring when freezing rain or drizzle hits a surface. It is similar in appearance to clear ice, which forms from supercooled water droplets. It is a relatively common occurrence in temperate climates in the winter when precipitation forms in warm air aloft and falls into below-freezing temperature at the surface.