Weather sources — Part 107 practice questions

43 practice questions on weather sources from the FAA remote pilot knowledge test, each with the correct answer and why it is correct.

1. 01

   What does the notation 'VC' indicate in a METAR report?

   • Very Clear conditions
   • Vicinity, indicating weather phenomena 5-10 miles from the airportCorrect
   • Variable Ceiling
   • Volcanic Cloud in the area
   Why

   Vicinity: the phenomenon is between 5 and 10 miles from the airport rather than at it. For a remote pilot it is a useful early warning — VCTS means thunderstorms are close enough to matter within the time an operation takes.

2. 02

   How are temperatures below 0°C indicated in a METAR?

   • With a minus sign (-)
   • Preceded by the letter 'M'Correct
   • In Fahrenheit instead of Celsius
   • With the letter 'C' for cold
   Why

   With a leading M for minus, as in M05 for five below. The format avoids the minus sign because the report is transmitted through systems where a stray hyphen is easily lost — and a dropped sign would turn ten below into ten above.

3. 03

   Which of the following is NOT mentioned as a type of aviation forecast pilots should be familiar with?

   • Terminal aerodrome forecast (TAF)
   • Aviation area forecast (FA)
   • Winds and temperatures aloft forecast (FB)
   • Pilot weather report (PIREP)Correct
   Why

   A PIREP is a report, not a forecast — it is an observation passed on by a pilot who has just flown through the conditions. The forecast products are the TAF, the area forecast, and winds and temperatures aloft.

4. 04

   How often are Terminal Aerodrome Forecasts (TAFs) typically updated?

   • Every hour
   • Twice daily
   • Four times a dayCorrect
   • Once a day
   Why

   Four times a day, covering a five statute mile radius around the airport. That radius is worth remembering: a TAF describes the airport's immediate vicinity, so a site some distance away may not be represented by it at all.

5. 05

   For which of the following conditions are Convective SIGMETs NOT issued?

   • Severe thunderstorms with surface winds greater than 50 knots
   • Hail at the surface greater than or equal to ¾ inch in diameter
   • Tornadoes
   • Light rain showers affecting a small areaCorrect
   Why

   Light rain over a small area does not meet any threshold. A Convective SIGMET is reserved for severe thunderstorms with surface winds above 50 knots, hail three-quarters of an inch or larger, tornadoes, and embedded or line thunderstorms — the conditions that endanger aircraft rather than merely inconvenience them.

6. 06

   How is a forecast visibility greater than six miles coded in a TAF?

   • 6+
   • P6SMCorrect
   • >6
   • UNLTD
   Why

   P6SM, where P means "plus". Six statute miles is the ceiling of the scale rather than a measurement: beyond it the difference stops mattering for the decisions the forecast supports, so it is not resolved further.

7. 07

   Which of the following is NOT mentioned as a contributor to aviation weather services?

   • National Weather Service (NWS)
   • Federal Aviation Administration (FAA)
   • Department of Defense (DOD)
   • National Transportation Safety Board (NTSB)Correct
   Why

   The NTSB investigates accidents; it produces no weather products. Aviation weather is a joint effort of the National Weather Service, the FAA and the Department of Defense, alongside other aviation groups.

8. 08

   What role do automated weather sources like AWOS and ASOS play in surface aviation weather observations?

   • They provide long-term climate data only
   • They play a major role in gathering surface observationsCorrect
   • They are used exclusively for high-altitude weather information
   • They are only used as backup systems when human observers are unavailable
   Why

   They do the bulk of the work, reporting continuously at fields where no observer is present. That continuity is their value to a remote pilot — an automated station gives current conditions at the field at the moment you check, not a reading taken hours ago.

9. 09

   Which of the following is NOT mentioned as part of the information provided in surface observations?

   • Wind
   • Visibility
   • Temperature/dew point
   • Fuel availabilityCorrect
   Why

   Fuel availability is an airport service, not a weather element — it appears in the Chart Supplement. A surface observation carries wind, visibility, temperature and dew point, sky condition and altimeter setting.

10. 10

    What is the purpose of aviation weather reports?

    • To predict long-term climate changes
    • To give accurate depictions of current weather conditionsCorrect
    • To provide maintenance schedules for weather equipment
    • To list available flight routes
    Why

    To describe conditions as they are now, accurately. Reports and forecasts do different jobs and the distinction matters when deciding whether to fly: a report tells you what is happening, a forecast tells you what is expected, and only one of them can be wrong about the present.

11. 11

    How is wind speed reported in a METAR when it exceeds 99 knots?

    • It is not reported
    • It is reported with five digits
    • It is reported with six digitsCorrect
    • It is reported in miles per hour instead of knots
    Why

    Six digits instead of five. The convention is positional: normally three digits of direction and two of speed, and speeds of 100 knots or more simply take a third digit. The field grows rather than changing units.

12. 12

    What does 'TEMPO' indicate in a TAF?

    • A permanent change in weather conditions
    • Temporary fluctuations of weather expected to last less than 1 hourCorrect
    • A 30% probability of thunderstorms
    • The end of the forecast period
    Why

    Temporary fluctuations expected to last under an hour, in conditions otherwise as forecast. TEMPO is the group that catches people out — it describes something real that is expected to occur, so a TEMPO for conditions below your minimums is a reason to reconsider, not a footnote.

13. 13

    How is runway visual range (RVR) reported in a METAR?

    • In statute miles
    • As a percentage of normal visibility
    • With an R, runway number, and visual range in feetCorrect
    • Only when visibility is less than one mile
    Why

    An R, the runway number, and the range in feet — feet rather than the statute miles used for prevailing visibility, because RVR measures along one specific runway rather than around the field. Two different visibility figures in the same report describe two different things.

14. 14

    How are cloud heights reported in a METAR?

    • In meters above ground level
    • With a three-digit number in hundreds of feet AGLCorrect
    • In kilometers above sea level
    • As a percentage of total sky coverage
    Why

    Three digits in hundreds of feet, above ground level. So 025 is 2,500 feet AGL. Reading it as feet directly is the classic error, and it matters under part 107, where the 500-foot cloud clearance requirement is measured against exactly this figure.

15. 15

    What does METAR stand for?

    • Meteorological Terminal Air ReportCorrect
    • Military Emergency Transmission and Response
    • Modern Equipment for Tracking Atmospheric Readings
    • Measured Environmental Conditions and Radar
    Why

    Meteorological Terminal Air Report — an observation of current surface weather in a standard international format. Because the format is international, the same report can be read at any airport in the world, which is why it is terse and coded rather than written out.

16. 16

    In a TAF, how is the forecast wind direction and speed typically reported?

    • In miles per hour with a compass direction
    • As a five-digit number group indicating direction and speed in knotsCorrect
    • Using the Beaufort scale
    • Only when wind speed exceeds 15 knots
    Why

    The same five-digit group a METAR uses — three digits of direction, two of speed, in knots. Report and forecast share the encoding deliberately, so the two can be read against each other without translating between formats.

17. 17

    What signals that a thunderstorm cell has entered the mature stage?

    • Formation of cumulus clouds
    • Precipitation beginning to fall from the cloud baseCorrect
    • Dissipation of the cloud
    • Increase in temperature at ground level
    Why

    Rain beginning to fall from the cloud base. It is the visible proof that a downdraft has formed alongside the updraft, and the mature stage is the most violent — updraft and downdraft side by side is what produces the worst turbulence and the strongest surface gusts.

18. 18

    How does an increase in density altitude affect aircraft performance?

    • It improves aircraft performance
    • It has no effect on aircraft performance
    • It decreases aircraft performanceCorrect
    • It only affects large aircraft, not small UAS
    Why

    It reduces it. High density altitude means thin air: propellers generate less thrust, and the aircraft climbs more slowly, carries less and drains its battery faster. Small unmanned aircraft are not exempt — with fixed-pitch propellers and limited power margin they feel it more sharply than a large aircraft does.

19. 19

    Which combination of conditions would most likely result in high density altitude?

    • Low elevation, high pressure, low temperature
    • High elevation, low pressure, high temperatureCorrect
    • Low elevation, low pressure, low temperature
    • High elevation, high pressure, low temperature
    Why

    High elevation, low pressure and high temperature — all three thinning the air in the same direction. It is the classic hot-day-at-altitude combination, and it can leave an aircraft that flies perfectly at sea level struggling to climb at all.

20. 20

    How does air pressure relate to air density at a constant temperature?

    • They are inversely proportional
    • They are directly proportionalCorrect
    • They have no relationship
    • The relationship varies depending on altitude
    Why

    Directly: compress air and you pack more molecules into the same volume. So higher pressure means denser air and better performance, which is why a falling barometer degrades an aircraft's climb even before any weather arrives.

21. 21

    What is the standard sea level pressure in inches of mercury ("Hg)?

    • 30.00 "Hg
    • 29.92 "HgCorrect
    • 28.92 "Hg
    • 31.00 "Hg
    Why

    29.92 inches of mercury, paired with 15 °C, as the International Standard Atmosphere reference. It is a datum rather than a typical reading — real conditions are compared against it, which is how density altitude is derived in the first place.

22. 22

    Why is low-level wind shear considered especially hazardous?

    • It only affects large aircraft
    • It occurs close to the groundCorrect
    • It's easy to predict and avoid
    • It only happens at high altitudes
    Why

    Because it happens close to the ground, where there is no height to trade for recovery. A sudden change in speed or direction that would be manageable at altitude arrives with no room underneath it, and small unmanned aircraft spend their whole flight in that layer.

23. 23

    What is the typical lifespan of a microburst?

    • 1-2 minutes
    • 5-15 minutesCorrect
    • 30-60 minutes
    • Several hours
    Why

    5 to 15 minutes — brief enough that it can develop and dissipate entirely within one flight, and short enough that it may never appear in a forecast. That transience is what makes it dangerous: the hazard arrives faster than any product will warn you about it.

24. 24

    What characterizes an unstable atmosphere?

    • Resistance to vertical air movement
    • Small vertical disturbances that quickly disappear
    • Tendency for small vertical air movements to become largerCorrect
    • Always calm and clear weather conditions
    Why

    Small vertical movements grow rather than damping out. A parcel nudged upward keeps rising, which is how cumulus builds into cumulonimbus. Stable air does the opposite — the disturbance fades — and gives smooth conditions with poorer visibility.

25. 25

    What happens when the air temperature reaches the dew point?

    • The air becomes completely dry
    • Thunderstorms always form
    • Moisture begins to condense out of the airCorrect
    • Wind speed increases dramatically
    Why

    The air is saturated and moisture begins condensing out — as fog, cloud or dew. Watching the two figures converge in successive observations is a practical warning that visibility is about to deteriorate, often faster than a forecast suggests.

26. 26

    What is the maximum speed of updrafts and downdrafts that a small UA might experience in a thunderstorm?

    • 1,000 fpm
    • 2,000 fpm
    • 3,000 fpm
    • More than 3,000 fpmCorrect
    Why

    More than 3,000 feet per minute — far beyond the climb or descent authority of any small unmanned aircraft. That is the point of the figure: inside a thunderstorm the aircraft goes where the air goes, and nothing on the control station changes that.

27. 27

    What does the presence of standing lenticular altocumulus clouds indicate?

    • Calm weather conditions
    • Light precipitation
    • Very strong turbulenceCorrect
    • High humidity
    Why

    Very strong turbulence. They form on the crests of mountain waves and appear deceptively smooth and stationary — a lens-shaped cloud sitting motionless while the air pours through it at speed. Their calm appearance is precisely why the warning has to be learned rather than inferred.

28. 28

    Which of the following is NOT a characteristic of an unstable air mass?

    • Cumuliform clouds
    • Showery precipitation
    • Rough air (turbulence)
    • Continuous precipitationCorrect
    Why

    Continuous precipitation belongs to stable air, where gentle widespread lift produces layered cloud and steady rain. Unstable air gives the opposite signature: cumuliform cloud, showery precipitation and turbulence — intermittent and vigorous rather than persistent and mild.

29. 29

    What wind speed at mountain top level suggests some turbulence?

    • 10 knots
    • 25 knotsCorrect
    • 40 knots
    • 50 knots
    Why

    25 knots at ridge level is the point at which some turbulence should be expected; 40 knots and above suggests severe. The relevant wind is the one at the peaks, not at the surface where you are standing — the two can differ enormously.

30. 30

    How many stages are in a thunderstorm cell's life cycle?

    • Two
    • ThreeCorrect
    • Four
    • Five
    Why

    Three: cumulus, mature and dissipating. The mature stage is the dangerous one, marked by the onset of precipitation at the surface, and a storm can pass through the whole cycle in well under an hour — which is why a distant cell is a reason to finish rather than to keep watching.

31. 31

    What is the key feature of the cumulus stage of a thunderstorm?

    • Downdraft
    • UpdraftCorrect
    • Lightning
    • Heavy precipitation
    Why

    The updraft. Every thunderstorm begins as a cumulus cloud being built by rising air, and in this first stage there is no precipitation yet — the updraft is still strong enough to hold everything aloft. Lightning and heavy rain belong to the stage that follows.

32. 32

    What characterizes the dissipating stage of a thunderstorm?

    • Strong updrafts
    • Heavy precipitation
    • DowndraftsCorrect
    • Increased lightning activity
    Why

    Downdrafts throughout the cell. The updraft that sustained it has been cut off, so the storm collapses under falling air and rain. Dissipating does not mean harmless — the outflow spreading from the base can still produce strong, sudden surface winds well away from the cloud.

33. 33

    What is a frontal zone or front?

    • A area of uniform weather conditions
    • The center of a high pressure system
    • The zone between two different air massesCorrect
    • A region of constant temperature and humidity
    Why

    The boundary between two air masses of different properties. Fronts matter because change concentrates there — wind shifts, temperature moves and cloud develops along the boundary, so a front crossing your site during an operation means the conditions you planned for will not be the ones you fly in.

34. 34

    What are the two necessary conditions for structural icing in flight?

    • High altitude and low visibility
    • Strong winds and heavy precipitation
    • Visible moisture and freezing temperature at the point of contactCorrect
    • Clear skies and extremely cold temperatures
    Why

    Visible moisture, and a temperature at or below freezing where it strikes the aircraft. Both are required — freezing air in clear conditions deposits nothing, and cloud above freezing merely wets the airframe. On a small unmanned aircraft even a light accumulation changes the propeller's shape and the weight it must lift.

35. 35

    Which two atmospheric factors are identified as having a major effect on aircraft performance?

    • Humidity and wind speed
    • Pressure and temperatureCorrect
    • Visibility and cloud cover
    • Precipitation and turbulence
    Why

    Pressure and temperature, because between them they set air density — and density is what a propeller has to work against. Humidity matters too but its contribution is much smaller, which is why these two lead.

36. 36

    How does temperature affect air density at a constant pressure?

    • Increasing temperature increases density
    • Increasing temperature decreases densityCorrect
    • Temperature has no effect on density
    • The relationship depends on humidity
    Why

    Inversely — heat makes air expand, so the same volume holds fewer molecules. This is the factor that changes most within a single working day: an aircraft that performed well at dawn has measurably less to work with by mid-afternoon on the same site.

37. 37

    How does increased humidity affect air density and aircraft performance?

    • It increases air density and improves performance
    • It decreases air density and reduces performanceCorrect
    • It has no significant effect on density or performance
    • It increases air density but reduces performance
    Why

    Humid air is less dense, so performance drops. It is counterintuitive, since damp air feels heavy, but water vapour molecules are lighter than the nitrogen and oxygen they displace. The effect is small next to temperature and pressure — it compounds them rather than driving the result.

38. 38

    How do ground obstructions affect wind patterns?

    • They have no effect on wind patterns
    • They only affect wind direction, not speed
    • They can create rapidly changing wind gusts in both direction and speedCorrect
    • They always reduce wind speed
    Why

    Buildings, trees and terrain break smooth flow into gusts that change speed and direction rapidly and unpredictably. This is the most common weather hazard a small unmanned aircraft actually meets, because it operates in exactly the layer where the disturbance lives — often on the lee side of a building that looked like shelter.

39. 39

    Which combination of conditions typically leads to the greatest atmospheric instability?

    • Cool and dry air
    • Warm and moist airCorrect
    • Cool and moist air
    • Warm and dry air
    Why

    Warm and moist. Warmth supplies the buoyancy and moisture supplies the energy released as it condenses, which is what lets a rising parcel keep accelerating. Cool dry air is the stable opposite.

40. 40

    What is a temperature inversion?

    • When temperature decreases with altitude
    • When temperature remains constant with altitude
    • When temperature increases with altitudeCorrect
    • When temperature fluctuates randomly with altitude
    Why

    A layer where temperature rises with altitude instead of falling. It caps vertical motion, so the air beneath becomes very stable — and everything in it stays there. Smooth flying, but haze, smoke and poor visibility collect under the inversion.

41. 41

    What type of cloud is considered the most dangerous to pilots?

    • Stratus
    • Cirrus
    • CumulonimbusCorrect
    • Nimbostratus
    Why

    Cumulonimbus. It carries every hazard at once — severe turbulence, lightning, hail, icing and violent up- and downdrafts — and it is built by the rising currents that make it turbulent in the first place. It should be avoided entirely rather than negotiated.

42. 42

    How is visibility defined in aviation?

    • The vertical distance from the ground to the cloud base
    • The greatest horizontal distance at which prominent objects can be viewed with the naked eyeCorrect
    • The distance between two airports
    • The maximum altitude at which an aircraft can fly
    Why

    The greatest horizontal distance at which prominent objects can be seen and identified with the naked eye. Horizontal is the operative word, and "naked eye" links it directly to part 107, whose 3 statute mile minimum is measured from the control station under exactly this definition.

43. 43

    How is a ceiling defined for aviation purposes?

    • The highest altitude at which an aircraft can fly
    • The lowest layer of clouds reported as broken or overcastCorrect
    • The maximum visibility reported by weather stations
    • The altitude at which precipitation begins to form
    Why

    The lowest broken or overcast layer, or the vertical visibility into an obscuration. Scattered cloud does not count — a layer has to cover more than half the sky before it is treated as a ceiling, which is why a low scattered deck and a low ceiling are reported differently.