ALL, SPO C— cool, dense air moving inland from over the

3381. Every physical process of weather is water.

accompanied by, or is the result of, a
A— movement of air.
B— pressure differential. ALL
C— heat exchange. 3383. A temperature inversion would most
likely result in which weather condition?
Every physical process of weather is accompanied A— Clouds with extensive vertical development
by, or is a result of, unequal heating of the Earth’s above an inversion aloft.
surface. (PLT512) — AC 00-6 B— Good visibility in the lower levels of the
atmosphere and poor visibility above an
inversion aloft.
ALL, SPO C— An increase in temperature as altitude is
3382. What causes variations in altimeter increased.
settings between weather reporting points?
A— Unequal heating of the Earth’s surface.
B— Variation of terrain elevation. ALL
C— Coriolis force. 3384. The most frequent type of ground or
surface-based temperature inversion is that
All altimeter settings are corrected to sea level. which is produced by
Unequal heating of the Earth’s surface causes A— terrestrial radiation on a clear, relatively still
pressure differences. (PLT165) — AC 00-6 night.
B— warm air being lifted rapidly aloft in the
vicinity of mountainous terrain.
ALL C— the movement of colder air under warm air, or
3395. The wind at 5,000 feet AGL is the movement of warm air over cold air.
southwesterly while the surface wind is
southerly. This difference in direction is
primarily due to ALL, SPO
A— stronger pressure gradient at higher 3397. What is meant by the term
altitudes. “dewpoint”?
B— friction between the wind and the surface. A— The temperature at which condensation and
C— stronger Coriolis force at the surface. evaporation are equal.
B— The temperature at which dew will always
Friction between the wind and the surface slows form.
the wind. The Coriolis force has less affect on C— The temperature to which air must be
slower winds, therefore there will be less cooled to become saturated.
deflection with surface winds than with winds at
5,000 feet AGL. (PLT516) — AC 00-6 Dew point is the temperature to which air must be
Answer (A) is incorrect because pressure gradient is not the
reason for wind direction differences; it is the force which causes
cooled to become saturated by the water vapor
wind. Answer (C) is incorrect because slower wind speed results in already present in the air. (PLT512) — AC 00-6
weaker Coriolis force at the surface.

ALL
ALL 3398. The amount of water vapor which air
3450. Convective circulation patterns can hold depends on the
associated with sea breezes are caused by A— dewpoint.
A— warm, dense air moving inland from over B— air temperature.
the water. C— stability of the air.
B— water absorbing and radiating heat faster
than the land.
Temperature largely determines the maximum
amount of water vapor air can hold. (PLT512) — AC
00-6
ALL, SPO Temperature is one of the most easily
3399. Clouds, fog, or dew will always form recognized discontinuities across a front.
when (PLT511) — AC 00-6
A— water vapor condenses. Answer (B) is incorrect because cloud coverage is not
B— water vapor is present. always present across a front. Answer (C) is incorrect
because relative humidity is not an easily recognized
C— relative humidity reaches 100 percent. discontinuity across a front.

As water vapor condenses or sublimates on

condensation nuclei, liquid or ice particles begin to ALL
grow. Some condensation nuclei have an affinity for 3423. One weather phenomenon which will
water and can induce condensation or sublimation always occur when flying across a front is
even when air is almost, but not completely, a change in the
saturated. (PLT512) — AC 00-6 A— wind direction.
B— type of precipitation.
C— stability of the air mass.
ALL
3400. What are the processes by which Wind direction always changes across a front.
moisture is added to unsaturated air? (PLT511) — AC 00-6
Answer (B) is incorrect because precipitation does not always exist
A— Evaporation and sublimation. with a front. Answer (C) is incorrect because the stability on both
B— Heating and condensation. sides of the front may be the same.
C— Supersaturation and evaporation.

Evaporation is the changing of liquid water to ALL

invisible water vapor. Sublimation is the changing of 3385. Which weather conditions should be
solid water directly to the vapor phase or water expected beneath a low-level temperature
vapor to ice, by passing the liquid state in each inversion layer when the relative humidity
process. (PLT512) — AC 00-6 is high?
A— Smooth air, poor visibility, fog, haze, or low
clouds.
ALL B— Light wind shear, poor visibility, haze, and
3444. If the temperature/dewpoint spread is light rain.
small and decreasing, and the temperature C— Turbulent air, poor visibility, fog, low stratus
is 62°F, what type weather is most likely to type clouds, and showery precipitation.
develop?
A ground-based inversion leads to poor visibility by
A— Freezing precipitation.
B— Thunderstorms. trapping fog, smoke, and other restrictions into low
C— Fog or low clouds. levels of the atmosphere. The layer is stable and
convection is suppressed. (PLT301) — AC 00-6
With a small temperature/dew point spread, the air
is close to saturation. This will usually result in fog or
low clouds. Anticipate fog when the ALL
3403. What measurement can be used to
temperature/dew point spread is 5°F or less and
determine the stability of the atmosphere?
decreasing. (PLT512) — AC 00-6
A— Atmospheric pressure.
B— Actual lapse rate.
ALL C— Surface temperature.
3422. One of the most easily recognized
discontinuities across a front is The difference between the existing lapse rate of a
given mass of air and the adiabatic rates of cooling
A— a change in temperature.
B— an increase in cloud coverage. in upward moving air determines if the air is stable
C— an increase in relative humidity. or unstable. (PLT173) — AC 00-6
ALL
3404. What would decrease the stability of
an air mass?
ALL
A— Warming from below. 3413. What are characteristics of unstable
B— Cooling from below. air?
C— Decrease in water vapor.
A— Turbulence and good surface visibility.
When air near the surface is warm and moist, B— Turbulence and poor surface visibility.
suspect instability. Surface heating, cooling aloft, C— Nimbostratus clouds and good surface
converging or upslope winds, or an invading mass of visibility.
colder air may lead to instability and cumuliform Characteristics of an unstable air mass include
clouds. (PLT173) — AC 00-6 cumuliform clouds, showery precipitation, rough
air (turbulence), and good visibility (except in
blowing obstructions). (PLT511) — AC 00-6
ALL, SPO
3405. What is a characteristic of stable air?
A— Stratiform clouds. ALL
B— Unlimited visibility. 3414. A stable air mass is most likely to
C— Cumulus clouds. have which characteristic?
A— Showery precipitation.
Since stable air resists convection, clouds in B— Turbulent air.
stable air form in horizontal, sheet-like layers or C— Poor surface visibility.
“strata.” (PLT173) — AC 00-6
Answers (B) and (C) are incorrect because unlimited Characteristics of a stable air mass include stratiform
visibility and cumulus clouds are characteristics of unstable clouds and fog, continuous precipitation, smooth air,
air.
and fair to poor visibility in haze and smoke.
(PLT511) — FAA-H-8083-25
ALL
3408. What feature is associated with a
temperature inversion? ALL
3406. Moist, stable air flowing upslope can
A— A stable layer of air.
be expected to
B— An unstable layer of air.
C— Chinook winds on mountain slopes. A— produce stratus type clouds.
B— cause showers and thunderstorms.
If the temperature increases with altitude through a C— develop convective turbulence.
layer (an inversion), the layer is stable and When stable air is forced upward the air tends to
convection is suppressed. (PLT492) — AC 00-6 retain horizontal flow and any cloudiness is flat
and stratified. (PLT192) — AC 00-6
ALL, SPO
3412. What are characteristics of a moist, ALL, SPO
unstable air mass? 3407. If an unstable air mass is forced
A— Cumuliform clouds and showery upward, what type clouds can be
precipitation. expected?
B— Poor visibility and smooth air. A— Stratus clouds with little vertical
C— Stratiform clouds and showery precipitation. development.
B— Stratus clouds with considerable associated
Characteristics of a moist, unstable air mass include turbulence.
cumuliform clouds, showery precipitation, rough air C— Clouds with considerable vertical
(turbulence), and good visibility (except in blowing development and associated turbulence.
obstructions). (PLT511) — AC 00-6
When unstable air is forced upward, the disturbance
grows. Any resulting cloudiness shows extensive
vertical development. (PLT192) — AC 00-6
ALL
3424. Steady precipitation preceding a
front is an indication of
ALL
A— stratiform clouds with moderate 3410. At approximately what altitude above
turbulence. the surface would the pilot expect the base
B— cumuliform clouds with little or no of cumuliform clouds if the surface air
turbulence. temperature is 82°F and the dewpoint is
C— stratiform clouds with little or no
38°F?
turbulence.
A— 9,000 feet AGL.
Precipitation from stratiform clouds is usually B— 10,000 feet AGL.
steady and there is little or no turbulence. C— 11,000 feet AGL.
(PLT511) — AC 00-6
When lifted, unsaturated air cools at approximately
5.4°F per 1,000 feet. The dew point cools at
ALL approximately 1°F per 1,000 feet. Therefore, the
3433. The conditions necessary for the
convergence of the temperature and dew point lapse
formation of cumulonimbus clouds are a
rates is 4.4°F per 1,000 feet. The base of a cloud
lifting action and
(AGL) that is formed by vertical currents can be
A— unstable air containing an excess of
roughly calculated by dividing the difference
condensation nuclei.
B— unstable, moist air. between the surface temperature and the dew point
C— either stable or unstable air. by 4.4 and multiplying the rounded result by 1,000.

For a cumulonimbus cloud or thunderstorm to

form, the air must have: ALL, SPO
3415. The suffix “nimbus,” used in naming
1. Sufficient water vapor,
clouds, means
2. An unstable lapse rate, and
A— a cloud with extensive vertical
3. An initial upward boost (lifting) to start the development.
storm process in motion. B— a rain cloud.
(PLT192) — AC 00-6 C— a middle cloud containing ice pellets.

The prefix “nimbo-” or suffix “-nimbus” means rain

ALL cloud. (PLT192) — AC 00-6
3409. What is the approximate base of the
cumulus clouds if the surface air
temperature at 1,000 feet MSL is 70°F and ALL
the dewpoint is 48°F? 3416. Clouds are divided into four families
A— 4,000 feet MSL. according to their
B— 5,000 feet MSL. A— outward shape.
C— 6,000 feet MSL. B— height range.
C— composition.
When lifted, unsaturated air cools at approximately
5.4°F per 1,000 feet. The dew point cools at For identification purposes, clouds are divided into
approximately 1°F per 1,000 feet. Therefore, the four families: high clouds, middle clouds, low clouds,
convergence of the temperature and dew point lapse and clouds with extensive vertical development.
rates is 4.4°F per 1,000 feet. The base of a cloud (PLT192) — AC 00-6
(AGL) that is formed by vertical currents can be
roughly calculated by dividing the difference
between the surface temperature and the dew point
by 4.4 and multiplying the rounded result by 1,000.
ALL Showers can result from these clouds. Expect very
3419. What clouds have the greatest strong turbulence, and perhaps some clear icing
turbulence?
above the freezing level. (PLT192) — AC 00-6
A— Towering cumulus.
B— Cumulonimbus.
C— Nimbostratus. ALL
3425. Possible mountain wave turbulence
Cumulonimbus are the ultimate manifestation of could be anticipated when winds of 40
instability. They are vertically-developed clouds knots or greater blow
of large dimensions with dense boiling tops,
often crowned with thick veils of dense cirrus A— across a mountain ridge, and the air is
(the anvil). Nearly the entire spectrum of flying stable.
hazards are contained in these clouds including B— down a mountain valley, and the air is
violent turbulence. (PLT192) — AC 00-6 unstable.
C— parallel to a mountain peak, and the air
is stable.
ALL
3417. An almond or lens-shaped cloud Always anticipate possible mountain wave
which appears stationary, but which may turbulence when strong winds of 40 knots or greater
contain winds of 50 knots or more, is blow across a mountain or ridge and the air is stable.
referred to as (PLT263) — AC 00-6
A— an inactive frontal cloud.
B— a funnel cloud.
ALL
C— a lenticular cloud.
3442. Upon encountering severe
Crests of standing waves may be marked by turbulence, which flight condition should
stationary, lens-shaped clouds known as the pilot attempt to maintain?
standing lenticular clouds. (PLT192) — AC 00-6 A— Constant altitude and airspeed.
B— Constant angle of attack.
C— Level flight attitude.
ALL
3418. Crests of standing mountain waves The primary concern is to avoid undue stress on the
may be marked by stationary, lens-shaped airframe. This can best be done by attempting to
clouds known as
maintain a constant attitude while keeping the
A— mammatocumulus clouds. airspeed below design maneuvering speed (V A).
B— standing lenticular clouds. (PLT263) — AC 00-6
C— roll clouds.

Crests of standing waves may be marked by ALL

stationary, lens-shaped clouds known as standing 3434. What feature is normally associated
lenticular clouds. (PLT192) — AC 00-6 with the cumulus stage of a thunderstorm?
A— Roll cloud.
B— Continuous updraft.
ALL, SPO
C— Frequent lightning.
3420. What cloud types would indicate
convective turbulence?
The key feature of the cumulus stage is an updraft.
A— Cirrus clouds. Precipitation beginning to fall from the cloudbase is
B— Nimbostratus clouds. the signal that a downdraft has developed also and a
C— Towering cumulus clouds.
cell has entered the mature stage. (PLT495) — AC
Towering cumulus signifies a relatively deep layer of 00-6
unstable air. They show considerable vertical
development and have billowing cauliflower tops.
ALL B— downdraft stage.
3435. Which weather phenomenon signals C— cumulus stage.
the beginning of the mature stage of a
thunderstorm? All thunderstorm hazards reach their greatest
A— The appearance of an anvil top. intensity during the mature stage. (PLT495) — AC
B— Precipitation beginning to fall. 00-6
C— Maximum growth rate of the clouds.

The key feature of the cumulus stage is an updraft. ALL, SPO

3439. Thunderstorms which generally
Precipitation beginning to fall from the cloudbase is
produce the most intense hazard to aircraft
the signal that a downdraft has developed also and
are
the cell has entered the mature stage. (PLT495) —
AC 00-6 A— squall line thunderstorms.
B— steady-state thunderstorms.
C— warm front thunderstorms.
ALL, SPO
A squall line is a non-frontal, narrow band of active
3436. What conditions are necessary for
thunderstorms. The line may be too long to easily
the formation of thunderstorms?
detour and too wide and severe to penetrate. It
A— High humidity, lifting force, and unstable
often contains severe steady-state thunderstorms
conditions.
B— High humidity, high temperature, and and presents the single, most intense weather
cumulus clouds. hazard to aircraft. (PLT495) — AC 00-6
C— Lifting force, moist air, and extensive cloud
cover.
ALL
For a cumulonimbus cloud or thunderstorm to 3440. A nonfrontal, narrow band of active
form, the air must have: thunderstorms that often develop ahead of
a cold front is known as a
1. Sufficient water vapor,
A— prefrontal system.
2. An unstable lapse rate, and B— squall line.
3. An initial upward boost (lifting) to start the C— dry line.
storm process in motion.
(PLT495) — AC 00-6 A squall line is a nonfrontal, narrow band of
active thunderstorms. The line may be too long
to easily detour and too wide and severe to
ALL penetrate. It often contains severe steady-state
3437. During the life cycle of a thunderstorms and presents the single, most
thunderstorm, which stage is characterized intense weather hazard to aircraft. (PLT495) —
predominately by downdrafts? AC 00-6
A— Cumulus.
B— Dissipating. ALL
C— Mature. 3441. If there is thunderstorm activity in
the vicinity of an airport at which you plan
Downdrafts characterize the dissipating stage of the
to land, which hazardous atmospheric
thunderstorm cell and the storm dies rapidly. phenomenon might be expected on the
(PLT495) — AC 00-6 landing approach?
A— Precipitation static.
ALL, SPO B— Wind-shear turbulence.
3438. Thunderstorms reach their greatest C— Steady rain.
intensity during the
Wind shear is an invisible hazard associated with all
A— mature stage.
thunderstorms. Shear turbulence has been
encountered 20 miles laterally from a severe storm.
(PLT495) — AC 00-6
ALL An increase in temperature with altitude is defined
3452. Which weather phenomenon is as a temperature inversion. A pilot can be relatively
always associated with a thunderstorm?
certain of a shear zone in the inversion if the pilot
A— Lightning. knows the wind at 2,000 to 4,000 feet is 25 knots or
B— Heavy rain. more. (PLT518) — AC 00-6
C— Hail.

A thunderstorm is, in general, a local storm

ALL
invariably produced by a cumulonimbus cloud, and is 3402. The presence of ice pellets at the
always accompanied by lightning and thunder. surface is evidence that there
(PLT495) — AC 00-6 A— are thunderstorms in the area.
B— has been cold frontal passage.
C— is a temperature inversion with freezing rain
ALL, SPO
at a higher altitude.
3426. Where does wind shear occur?
A— Only at higher altitudes. Ice pellets always indicate freezing rain at higher
B— Only at lower altitudes. altitude. (PLT301) — AC 00-6
C— At all altitudes, in all directions.

Wind shear may be associated with either a AIR, GLI, RTC, WSC, PPC
wind shift or a wind speed gradient at any level 3429. One in-flight condition necessary for
in the atmosphere. (PLT518) — AC 00-6 structural icing to form is
A— small temperature/dewpoint spread.
ALL, SPO B— stratiform clouds.
3427. When may hazardous wind shear be C— visible moisture.
expected?
Two conditions are necessary for structural icing
A— When stable air crosses a mountain barrier in flight:
where it tends to flow in layers forming
lenticular clouds. 1. The aircraft must be flying through visible
B— In areas of low-level temperature inversion, water such as rain or cloud droplets, and
frontal zones, and clear air turbulence. 2. The temperature at the point where the
C— Following frontal passage when moisture strikes the aircraft must be 0°C
stratocumulus clouds form indicating (32°F) or colder.
mechanical mixing. (PLT274) — AC 00-6

Hazardous wind shear can occur near the

ground with either thunderstorms or a strong AIR, GLI, RTC, WSC, PPC
temperature inversion. (PLT518) — AC 00-6 3430. In which environment is aircraft
Answer (A) is incorrect because turbulence can be expected when structural ice most likely to have the
stable air crosses a mountain barrier. Answer (C) is incorrect highest accumulation rate?
because turbulence can be expected following frontal passage
when stratocumulus clouds form, indicating mechanical mixing. A— Cumulus clouds with below freezing
temperatures.
B— Freezing drizzle.
ALL, SPO C— Freezing rain.
3428. A pilot can expect a wind-shear zone
in a temperature inversion whenever the A condition favorable for rapid accumulation of clear
windspeed at 2,000 to 4,000 feet above the icing is freezing rain below a frontal surface.
surface is at least (PLT274) — AC 00-6
A— 10 knots.
B— 15 knots.
C— 25 knots.
ALL B— An air mass moving inland from the
3956. During a cross-country flight you coast in winter.
picked up rime icing which you estimate is C— A light breeze blowing colder air out to
1/2" thick on the leading edge of the wings. sea.
You are now below the clouds at 2,000 feet
AGL and are approaching your destination Advection fog forms when moist air moves over
airport under VFR. Visibility under the colder ground or water. It is most common along
clouds is more than 10 miles, winds at the coastal areas. This fog frequently forms offshore as a
destination airport are 8 knots right down result of cold water, then is carried inland by the
the runway, and the surface temperature is wind. (PLT226) — AC 00-6
3°C. You decide to:
A— use a faster than normal approach and
landing speed. ALL
B— approach and land at your normal 3446. What types of fog depend upon wind
speed since the ice is not thick enough to in order to exist?
have any noticeable effect. A— Radiation fog and ice fog.
C— fly your approach slower than normal to B— Steam fog and ground fog.
lessen the “wind chill” effect and break up C— Advection fog and upslope fog.
the ice.
Advection fog forms when moist air moves over
Ice will accumulate unevenly on the airplane. It will
colder ground or water. It is most common along
add weight and drag, and decrease thrust and lift.
coastal areas, but often develops deep in continental
With ice accumulations, landing approaches should
areas. Advection fog deepens as wind speed
be made with a minimum wing flap setting and with
increases up to about 15 knots. Wind much stronger
an added margin of airspeed. Sudden and large
than 15 knots lifts the fog into a layer of low stratus
configuration and airspeed changes should be
or stratocumulus. Upslope fog forms as a result of
avoided. (PLT128) — FAA-H-8083-3
moist, stable air being cooled adiabatically as it
moves up sloping terrain. Once upslope wind ceases,
ALL the fog dissipates. (PLT226) — AC 00-6
3443. What situation is most conducive to
the formation of radiation fog?
ALL
A— Warm, moist air over low, flatland areas on 3447. Low-level turbulence can occur and
clear, calm nights. icing can become hazardous in which type
B— Moist, tropical air moving over cold, offshore of fog?
water.
C— The movement of cold air over much A— Rain-induced fog.
warmer water. B— Upslope fog.
C— Steam fog.
Conditions favorable for radiation fog are clear sky,
little or no wind, and small temperature/dew point Steam fog forms in the winter when cold, dry air
spread (high relative humidity). Radiation fog is passes from land areas over comparatively warm
restricted to land because water surfaces cool little ocean waters. Low-level turbulence can occur and
from nighttime radiation. (PLT226) — AC 00-6 icing can become hazardous in a steam fog. (PLT226)
— AC 00-6

ALL
3445. In which situation is advection fog
most likely to form?
A— A warm, moist air mass on the
windward side of mountains.
ALL C— Frost will cause the airplane to become
3401. Which conditions result in the airborne with a higher angle of attack,
formation of frost? decreasing the stall speed.
A— The temperature of the collecting surface is
at or below freezing when small droplets of The roughness of the surface of frost spoils the
moisture fall on the surface. smooth flow of air, thus causing a slowing of the
B— The temperature of the collecting surface is airflow. This slowing of the air causes early air flow
at or below the dewpoint of the adjacent air separation over the affected airfoil, resulting in a loss
and the dewpoint is below freezing. of lift. Even a small amount of frost on airfoils may
C— The temperature of the surrounding air is at prevent an aircraft from becoming airborne at
or below freezing when small drops of
normal takeoff speed. (PLT134) — FAA-H-8083-25
moisture fall on the collecting surface.

Frost forms in much the same way as dew. The differ-

AIR, GLI, RTC, WSC, PPC
ence is that the dew point of surrounding air must be 3431. Why is frost considered hazardous to
colder than freezing. (PLT493) — AC 00-6 flight?
A— Frost changes the basic aerodynamic shape
AIR of the airfoils, thereby increasing lift.
3432. How does frost affect the lifting B— Frost slows the airflow over the airfoils,
surfaces of an airplane on takeoff? thereby increasing control effectiveness.
C— Frost spoils the smooth flow of air over the
A. Frost may prevent the airplane from wings, thereby decreasing lifting capability.
becoming airborne at normal takeoff
speed. The roughness of the surface of frost spoils the
B. Frost will change the camber of the smooth flow of air, thus causing a slowing of the
wing, increasing lift during takeoff.
airflow. This slowing of the air causes early air flow
C. Frost may cause the airplane to
become airborne with a lower angle separation over the affected airfoil, resulting in a loss
of attack at a lower indicated of lift. Even a small amount of frost on airfoils may
airspeed. prevent an aircraft from becoming airborne at
normal takeoff speed. (PLT128) — AC 00-6
The roughness of the surface of frost spoils the
smooth flow of air, thus causing a slowing of the
airflow. This slowing of the air causes early air flow
separation over the affected airfoil, resulting in a loss
of lift. Even a small amount of frost on airfoils may
prevent an aircraft from becoming airborne at
normal takeoff speed. (PLT128) — AC 00-6

AIR, GLI
3206. How will frost on the wings of an
airplane affect takeoff performance?
A— Frost will disrupt the smooth flow of air over
the wing, adversely affecting its lifting
capability.
B— Frost will change the camber of the wing,
increasing its lifting capability.