When there is a small temperature and dew point spread, what weather phenomenon should a pilot be on the alert for?

When there is a small temperature and dew point spread, it indicates that the air is close to saturation. In this scenario, the air's ability to hold moisture is limited, leading to the potential for condensation. As humidity increases and the temperature nears the dew point, conditions are favorable for the formation of fog and low clouds.

Fog occurs when the air close to the ground cools enough to cause the water vapor in the air to condense into tiny water droplets, which creates a cloud layer at or near the surface. Similarly, low clouds can develop under these conditions, potentially leading to reduced visibility and challenging flying conditions. Hence, pilots should be particularly vigilant for these weather phenomena when the temperature and dew point are close together.

While other weather phenomena may occur under different atmospheric conditions, fog and low clouds are the most directly associated with a small temperature and dew point spread.