Which type of fog is most likely to occur on a clear, calm night?

Radiation fog is most likely to occur on a clear, calm night due to specific atmospheric conditions. On such nights, the ground loses heat rapidly through radiation, cooling the air just above it. If the air temperature near the ground cools to the dew point, moisture in the air condenses into tiny water droplets, forming fog.

This type of fog typically forms in areas where there is little wind, allowing the temperature to drop significantly. The clear skies contribute to the loss of heat, while calm conditions prevent the mixing of warmer air with the cooler air near the surface, allowing the air to reach saturation more effectively.

In contrast, advection fog generally forms when warm, moist air moves over cooler ground or water, creating a different set of conditions that are not primarily dependent on cooling from the ground. Upslope fog occurs when moist air ascends a slope, cooling as it rises, while ice fog forms in extremely cold conditions when water vapor sublimates directly into ice crystals. These conditions do not align with the characteristics of a clear, calm night, making radiation fog the most appropriate choice for that scenario.