The dew point is the temperature at which air must cool to reach saturation. Aviation weather reports usually provide both the dew point and the current air temperature. By comparing these two values, we can determine the proximity of the air to complete saturation, known as the temperature-dew point spread.

• In very dry conditions, the dew point is much lower than the air temperature, resulting in a high temperature-dew point spread. The air needs significant cooling to reach saturation.
• In very humid conditions, the dew point is close to the air temperature, resulting in a low temperature-dew point spread.

By examining the temperature and dew point spread, we can predict certain weather patterns:

• A large gap means clouds are less likely to form, except at higher altitudes, as the air would need to rise significantly and cool down enough for condensation to happen.
• A small gap between surface air temperature and dew point suggests a high likelihood of fog or low clouds.