What environmental condition typically signals the presence of upslope fog?

The presence of upslope fog is primarily associated with cool, moist air rising over terrain. As the air moves upward, it encounters a decrease in temperature, which can lead to condensation if the air cools enough to reach its dew point. This process is common in areas with hills or mountains, where the air is forced to ascend. The moisture in the air condenses into tiny water droplets, forming fog.

The other conditions listed do not foster the occurrence of upslope fog. For instance, high wind conditions would typically disperse fog rather than contribute to its formation. Warm temperatures with low humidity are also not conducive to fog, as the air's capacity to hold moisture would prevent condensation. Lastly, high-pressure systems often lead to clearing skies and stable atmospheric conditions, which are generally not associated with the moist, cooler conditions required for fog formation.