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An aerodrome on the coast (Faro, Portugal) reported the following METAR:

LPFR 070650Z 26010KT 0100FG VV/// 05/05 Q1006

What type of fog can you expect in Faro?

  • A

    Frontal fog

  • B

    Advection fog

  • C

    Radiation fog

  • D

    Orographic fog

Refer to figure.
Faro (LPFR) is a coastal airport which is prone to advection fog.

Advection fog is formed by the advection of warm, moist air over a cold surface – the air mass is cooled from below giving rise to an inversion. The surface can be land or sea and it can appear by day or night.

Conditions necessary for advection fog to form

  • WIND SPEEDS. Up to 15 kts to move the air (may be stronger over sea – up to 20 kts).

Wind speeds over 5 kts are sufficient for advection fog formation, but the speeds of around 15 kts provide the conditions for maximum vertical development of advection fog.

  • COLD SURFACE. Colder than the dew point of the air moving over it – to ensure condensation.
  • HUMID AIR. High relative humidity – so that relatively little cooling is required to produce saturation and subsequent condensation.
  • TEMPERATURE DIFFERENCE. The greater the temperature difference between the warmer air and the colder ground, the greater the likelihood of fog formation.

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