Meteorology · Humidity — Dewpoint
A small spread between the air temperature and the dewpoint indicates:
- AHigh relative humidity and an increased likelihood of fog or cloud as the air cools to the dewpoint✓ Correct
- BVery dry air and clear skies
- CRapidly rising pressure
- DAn approaching cold front
Explanation
The dewpoint is the temperature at which air becomes saturated. A small temperature–dewpoint spread means the air is near saturation (high relative humidity); slight cooling — e.g., at night or over cold water — readily produces fog or low cloud.
Authority: Bowditch (Pub. No. 9), humidity and dewpoint; WMO
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