Which term describes fog that typically forms overnight in calm conditions?

The term that accurately describes fog that typically forms overnight in calm conditions is ground fog. This type of fog forms as a result of radiational cooling, where the ground loses heat quickly during clear nights, causing the air near the surface to cool down to the dew point and condense into tiny water droplets. Ground fog usually develops in low-lying areas and can significantly reduce visibility, making it particularly relevant for pilots and drivers.

While sea fog pertains to fog that forms over the sea, particularly when warm, moist air moves over cooler ocean waters, and valley fog typically forms in valleys due to cold air pooling in lower elevations, ground fog is distinct because it occurs directly on the surface and is primarily influenced by ground temperature. Upslope fog, on the other hand, forms when moist air is lifted along a slope, cooling as it rises.

Understanding how these various types of fog form and their characteristics is crucial, especially for pilots, as fog can pose significant visibility issues during flight operations.