Radiation fog is most likely to form under which conditions?

Why →Radiation fog forms when the ground radiates heat on a clear, calm night, cooling surface air to the dew point. Clear skies allow maximum radiative cooling. Calm winds prevent the mixing that would disperse fog. High relative humidity means little cooling is needed to reach saturation. It is typically shallow, forms in low-lying areas, and dissipates quickly after sunrise.

The trap →Advection fog (not radiation fog) forms when warm moist air moves over a cold surface with winds up to 15 knots. Radiation fog requires calm conditions; wind would mix and disperse it. Overcast skies prevent radiative cooling, so it doesn't form under cloud cover.

Field note →Radiation fog is predictable: it forms overnight in valleys and burns off within 1–2 hours after sunrise. The same conditions that create early morning golden-hour shooting opportunities also create ground-level fog that can eliminate visual line of sight.