What type of fog is likely to persist for days, particularly when winds are less than 15 knots?

The type of fog that is likely to persist for days when winds are less than 15 knots is advection fog. This phenomenon occurs when warm, moist air moves over a cooler surface, leading to condensation and the formation of fog. Advection fog is often found along coastlines, where warm air from the ocean interacts with cooler land or water temperatures. The presence of less wind allows the conditions that created the fog to remain stable, leading to its persistence over an extended period.

In contrast, upslope fog forms when moist air is forced to rise over a topographical barrier, causing cooling and condensation. This type of fog may not last as long as advection fog, especially in the absence of wind. Steam fog, on the other hand, occurs when cold air moves over warmer water, leading to evaporation and subsequent condensation, but typically does not persist for days. Radiation fog develops on clear, still nights when the ground cools rapidly, causing moisture in the air close to the ground to condense, but it generally dissipates quickly with changes in temperature or with increased winds. Therefore, advection fog is the type that can continue for days in stable conditions, particularly with lower wind speeds.