Freezing drizzle is

drizzle Drizzle is a light precipitation which consists of liquid water drops that are smaller than those of rain – generally smaller than in diameter. Drizzle is normally produced by low stratiform clouds and stratocumulus clouds. Precipitation r ...

that freezes on contact with the ground or an object at or near the surface. Its

METAR METAR is a format for reporting weather information. A METAR weather report is predominantly used by aircraft pilots, and by meteorologists, who use aggregated METAR information to assist in weather forecasting. Raw METAR is highly standardize ...

code is FZDZ.

Formation

Although freezing drizzle and

freezing rain Freezing rain is rain maintained at temperatures below melting point, freezing by the ambient air mass that causes freezing on contact with surfaces. Unlike rain and snow mixed, a mixture of rain and snow or ice pellets, freezing rain is made en ...

are similar in that they both involve liquid

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

above the surface in subfreezing temperatures and freeze on the surface, the mechanisms leading to their development are entirely different. Where freezing rain forms when frozen precipitation falls through a melting layer and turns liquid, freezing drizzle forms via the ''supercooled warm-rain process'', in which cloud droplets coalesce until they become heavy enough to fall out of the cloud, but in subfreezing conditions. Despite this process taking place in a subfreezing environment, the liquid water will not freeze if the environmental temperature is above , via

supercooling Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid. Per the established international definition, supercooling means ''‘cooling a substance be ...

. If

ice crystals Ice crystals are solid water (known as ice) in crystal structure, symmetrical shapes including hexagonal crystal family, hexagonal columns, hexagonal plates, and dendrite (crystal), dendritic crystals. Ice crystals are responsible for various at ...

are already present in this environment, the liquid droplets will freeze onto these crystals and be effectively removed before they can grow large enough to fall out of the cloud. As a result, freezing drizzle develops in shallow low-level stratus-type clouds where air saturation occurs entirely below the layer in which ice crystals can develop and grow.

Effects

When freezing drizzle accumulates on land, it creates an icy layer of glaze. Freezing drizzle alone does not generally result in significant

ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...

accumulations due to its light, low-intensity nature unlike its rain counterpart. However, even thin layers of slick ice deposited on roads as black ice can be very slippery and cause extremely hazardous conditions resulting in vehicle crashes. Freezing drizzle is extremely dangerous to aircraft in icing conditions, as the supercooled water droplets will freeze onto the airframe, degrading aircraft performance considerably. The loss and accident of

American Eagle Flight 4184 American Eagle Flight 4184, officially operating as Simmons Airlines Flight 4184, was a scheduled domestic passenger flight from Indianapolis, Indiana, to Chicago, Illinois, United States. On , 1994, the performing this route flew into severe i ...

on October 31, 1994, has been attributed to ice buildup due to freezing drizzle aloft.

References

Precipitation Weather hazards {{Meteorology-stub

Formation

Effects

See also

References