What is advection fog?

Temperatures warmed into the lower 50s Monday, but the ground was still much colder, especially with a snow pack still visible in spots.

It's that contrast between the warmer air and cold ground that made the perfect recipe for fog, said Chief Meteorologist McCall Vrydaghs.

Advection fog is formed by the rush of warm moist over a cold ground or snow. During this process, the warmer air is cooled by the cold ground and the air becomes saturated at the lowest levels.

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The added moisture from rainfall on Monday also help to create the fog.

During extreme conditions, fog can thicken, visibility can drop and dense fog can become problematic.