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Weather Conditions

Frost

Frost: A deposit of small, white ice crystals formed on the ground or other surfaces. Frost is formed by sublimation, that is, when water vapour is deposited upon a surface whose temperature is at or below freezing.

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Freezing Fog

Freezing Fog: A suspension of numerous very small water droplets which freeze upon impact with the ground or other exposed objects; generally reduces the horizontal visibility at the earth’s surface to less than 1 km (5/8 mile).

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Freezing Drizzle

Freezing Drizzle: Fairly uniform precipitation composed exclusively of fine drops [diameter less than 0.5 mm (0.02 inch)] very close together, which freeze upon impact with the ground or other exposed objects.

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Ice Pellets

Ice Pellets: Precipitation of transparent (grains of ice) or translucent (small hail) pellets of ice, which are spherical or irregular, and have a diameter of 5 mm (0.2 inch) or less. Ice pellets usually bounce when hitting hard ground.

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Clear Ice

Clear Ice: Whenever precipitation falls on a cold-soaked aeroplane on the ground, clear icing may occur. Even in ambient temperatures between –2°C and +15°C, ice or frost can form in the presence of visible moisture or high humidity if the aeroplane structure remains at 0°C or below. Clear ice is …

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Dry snow

Dry snow: Snow from which a snowball cannot readily be made and that has a temperature less than 0°C. It has low adhesion to the surface, and can be removed with a brush.

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Wet Snow

Wet Snow: Snow, containing a great deal of liquid water, which can adhere and freeze on aircraft surfaces/engine area

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Active Frost

Active Frost: Active frost occurs when the aircraft surface temperature is at or below 0°C (32°F), and at or below dew point.

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