weather theoryFAA-published sample question (FIA, Aug 2021)
You may anticipate fog when the temperature-dew point spread is
A
15°F or less and decreasing.
B
15°F or more and increasing.
C
5°F or less and decreasing.✓ Correct Answer
Explanation
Fog forms when air cools to near its dewpoint, so a small temperature/dewpoint spread (about 5 degrees F or less) that is decreasing signals likely fog (PHAK Chapter 12). A 15-degree spread is far from saturation, and an increasing spread means the air is drying.
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