Advection fog forms when warm, moist air moves over a cooler surface, causing the air to cool and condense. This process typically occurs near coastlines, where warm air from the ocean meets cooler land or water. The result is a thick, low-lying fog that can reduce visibility significantly. This type of fog is common in coastal regions and can also occur in areas where warm air flows over cold ground or snow. Advection fog can develop quickly and may linger for hours or even days, impacting travel and outdoor activities due to low visibility conditions.