The measurement of “fogginess” is not simply about how dense the mist is, but rather the annual count of days when visibility drops below a specific, measurable threshold.
Defining the Phenomenon
Fog is scientifically defined as a cloud that forms at or near the Earth’s surface. It consists of microscopic water droplets or ice crystals suspended in the air, which form when the air cools to its dew point, reaching near 100% relative humidity.
Meteorologists quantify the phenomenon by setting a strict visibility criterion for official record-keeping. For a weather event to be classified as fog, the World Meteorological Organization specifies that horizontal visibility must be reduced to less than 1,000 meters, or 1 kilometer. If visibility is greater than this but still impaired, the condition is typically categorized as mist.
Identifying the World’s Foggiest Location
The location most consistently recognized as the foggiest place on Earth is the Grand Banks of Newfoundland, an area of continental shelf located off the southeast coast of Canada. This expansive, shallow region of the North Atlantic Ocean is perpetually shrouded in a dense, chilling haze. The Grand Banks experiences an average of more than 200 days of fog annually, with some specific measurements citing 206 foggy days per year.
The persistent low visibility here has long posed a significant hazard to maritime navigation, especially given the area’s historical importance as a rich fishing ground. While the Grand Banks holds the title, other locations are strong contenders, particularly coastal regions where warm and cold air masses meet. Point Reyes, California, for example, is another area known for its staggering frequency of fog, also recording over two hundred foggy days each year. Cape Disappointment, Washington, also represents a significant fog champion in the Pacific Northwest.
The Climate Mechanism Behind the Extreme Fog
The extreme and persistent fog at the Grand Banks is the result of a rare and powerful confluence of two major ocean currents. The cold, southward-flowing Labrador Current, which originates in the Arctic, carries frigid water along the coast of eastern Canada. This cold current meets the warm, northward-moving Gulf Stream, which brings tropical, moist air and water from the south.
The dramatic temperature difference between the two water masses creates the ideal conditions for a specific type of fog known as advection fog. As the warm, moisture-laden air from the Gulf Stream passes over the much colder water of the Labrador Current, the air mass rapidly cools from below. This sudden and intense cooling causes the water vapor in the air to condense almost immediately into a thick, low-lying cloud.
This process is intensified by the establishment of a temperature inversion, where a layer of warmer air rests above the cooling layer of air and fog near the surface. The inversion acts as a lid, trapping the dense fog close to the ocean’s surface and preventing it from mixing with the drier air above, leading to its prolonged persistence.