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JamesPeace
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Advection fog is the most widespread type likely to be encountered at sea and is caused by relatively warm air being cooled by flowing over a cooler sea surface. The latter will be below the dew point of the air and normally the wind speed will be between 4 and 16 knots. There are only certain localities where such conditions are relatively prevalent. One is off the Grand Banks of Newfoundland where the cold Labrador Current causes a decrease in sea temperature. The warm, moist, southerly airstream flowing over this is cooled below its dew point to form advection, or sea fog. The English Channel is often affected by advection fog when south-westerly winds reach the British Isles from the Azores in spring and early summer. In ocean regions, well away from the shallows and coastal waters, the sea surface temperature changes very little through solar heating or night radiation. Generally, the daily change in sea surface temperature is less than 0.5 degrees. It is possible to estimate the likelihood of the formation of fog from observations of air temperatures, wind and direction and other weather signs, plus a knowledge of sea temperatures to be expected on the course ahead.