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Freezing Fog

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Article Information
Category: Weather Weather
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WX
Tag(s) Weather Phenomena
Icing

FZFG

Definition

Fog comprised of supercooled water droplets which normally deposit rime ice on contact with an object with a surface temperature of less than 0°C273.15 K
32 °F
491.67 °R
. Fog is generally defined in terms of visibility being less than 1000m horizontally and freezing fog typically forms in the temperature range of -0°C273.15 K
32 °F
491.67 °R
to -20°C253.15 K
-4 °F
455.67 °R
. Freezing fog is reported as FZFG on a METAR report.

Description

Surface contact with subzero surface temperatures notwithstanding, water droplets will continue to exist in supercooled liquid form until the temperature drops below -10°C263.15 K
14 °F
473.67 °R
to -20°C253.15 K
-4 °F
455.67 °R
at which time the droplets are likely to freeze and become ice crystals (see Ice Fog).

Effects

Freezing Fog will leave only a thin film of frost or rime ice on an aircraft, which nevertheless needs to be removed before flight with a de-icing treatment. Aircraft should also receive an anti-ice treatment before commencing a take off if freezing fog conditions exist for the taxi and take off phases of flight in order to prevent further build up of ice.

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