A small temperature-dewpoint spread indicates what condition is likely?
- AStrong convective turbulence
- BRapidly rising barometric pressure
- Fog or low clouds forming
- DHigh visibility and stable conditions
A small temperature-dewpoint spread indicates what condition is likely?
Part 107 exam practice question · Weather & METAR
Explanation
Understanding the question
Dewpoint is the temperature at which air becomes saturated, so the spread between temperature and dewpoint measures how much cooling the air can take before its moisture condenses. A small spread means the air is close to saturation and needs only slight cooling — nightfall, a temperature drop, or air moving over cooler ground or water — to produce visible moisture in the form of fog or low cloud. That matters directly to a remote pilot because visual line of sight is a regulatory requirement and Part 107 also sets a minimum flight visibility and cloud clearance distances. Fog forming or a low ceiling descending can make a legal flight illegal within minutes, often faster than the pilot notices from the ground. The relationship also runs the other way: a spread that is widening through the morning indicates conditions improving. Watching the spread trend rather than the single number is what gives useful warning.
Why the correct answer is correct
A small temperature-dewpoint spread means the air is near saturation, so only slight cooling is needed for moisture to condense into fog or low cloud.
Background
Dewpoint is the temperature at which air becomes saturated. A small temperature-dewpoint spread indicates air near saturation and a likelihood of fog or low cloud. Part 107 requires three statute miles visibility and specified cloud clearances.
Close Together, Clouds Form
Close Together, Clouds Form. The spread is how much cooling the air can still take before the water shows up.
Exam tip
Connect it to the requirements: three statute miles flight visibility, 500 feet below and 2,000 feet horizontally from clouds. Fog formation puts both at risk.
Common mistakes
- •Reading the spread as an indicator of turbulence or pressure
- •Checking a single observation rather than the trend
- •Overlooking the cloud clearance requirements alongside visibility
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