SPC Aviation Weather Information 3 — Questions and Answers
Question 1: Which type of fog forms when warm, moist air moves over a cooler surface?
- Radiation fog
- Advection fog (Correct answer)
- Upslope fog
- Steam fog
Correct answer: Advection fog
Advection fog forms when warm moist air moves horizontally over a cooler surface, cooling the air to its dew point — common along coastlines and in spring over cold land.
Question 2: What weather phenomenon is most likely when the temperature and dew point spread is 5°F or less and is decreasing?
- Thunderstorm development
- Frost formation on aircraft surfaces
- Fog or low cloud formation (Correct answer)
- Pressure altitude errors in the altimeter
Correct answer: Fog or low cloud formation
A small and decreasing temperature-dew point spread indicates the air is approaching saturation, making fog or low cloud formation likely.
Question 3: Mountain wave turbulence is most likely to occur when winds at mountaintop level are:
- Light and variable, less than 20 knots
- At least 25 knots and perpendicular to the ridge (Correct answer)
- Primarily from the east at any speed
- Gusty with frequent direction changes
Correct answer: At least 25 knots and perpendicular to the ridge
Mountain wave turbulence is most severe when surface winds are at least 25 knots and blow nearly perpendicular (within 30°) to the ridge line.
Question 4: What is a lenticular cloud, and what does its presence indicate to a pilot?
- A flat stratus cloud indicating stable air and smooth flying
- A lens-shaped cloud forming in the crest of a mountain wave indicating turbulence (Correct answer)
- A cumulonimbus anvil indicating active thunderstorm development
- A funnel-shaped cloud indicating tornado activity
Correct answer: A lens-shaped cloud forming in the crest of a mountain wave indicating turbulence
Lenticular (lens-shaped) clouds form at the crest of mountain waves and are a visual signal of potentially severe turbulence and strong up/downdrafts in the area.
Question 5: What ceiling and visibility values define Instrument Meteorological Conditions (IMC)?
- Ceiling below 3,000 feet AGL or visibility less than 5 miles
- Ceiling below 1,000 feet AGL and/or visibility less than 3 miles (Correct answer)
- Ceiling below 500 feet AGL and visibility less than 1 mile
- Any overcast sky condition regardless of visibility
Correct answer: Ceiling below 1,000 feet AGL and/or visibility less than 3 miles
IMC exists when the ceiling is below 1,000 feet AGL and/or visibility is less than 3 miles, requiring instrument flight rules for flight.
Question 6: An area forecast (FA) covers weather conditions for an area how large?
- A single state or terminal control area
- A region covering several states (Correct answer)
- A 25-mile radius around the forecast station
- The contiguous United States only
Correct answer: A region covering several states
Area Forecasts (FA) cover large geographic regions encompassing several states, providing general aviation weather information including clouds, visibility, and hazards.
Question 7: The tropopause is significant to pilots primarily because:
- It marks the boundary where aircraft must transition to jet fuel
- Jet stream winds are strongest near the tropopause and it acts as a temperature inversion limiting convection (Correct answer)
- Radar coverage ends at the tropopause altitude
- VOR navigation signals are absorbed above the tropopause
Correct answer: Jet stream winds are strongest near the tropopause and it acts as a temperature inversion limiting convection
The tropopause is the boundary between the troposphere and stratosphere where temperature stops decreasing; jet stream winds concentrate near it and it caps convective activity.
SPC Aviation Weather Information 3
Which type of fog forms when warm, moist air moves over a cooler surface?