Final answer:
A pilot should be vigilant for fog or cloud formation when the temperature and dew point are close, suggesting air near saturation and potential icing conditions.
Step-by-step explanation:
With a small temperature and dew point spread, a pilot should be on the alert for the potential of fog or cloud formation, as these conditions signify that the air is nearly saturated with moisture. The dew point is the temperature at which the air can no longer hold all of its water vapor, and any further cooling will result in condensation. This condition is critical for aviation safety because it may lead to reduced visibility or icing conditions, which are hazardous during flight.
It is especially important to monitor when the temperatures are close to freezing, as this might indicate the possibility of ice formation on the aircraft surfaces. Pilots keep a close eye on the dew point because when the dew point is below 0°C, freezing temperatures are a greater possibility, posing a risk of icing. These weather conditions can have serious implications for the performance and handling of an aircraft.