SU unit 7 weather Flashcards
Every physical process of weather is accompanied by, or is the result of, a
heat exchange
What causes variations in altimeter settings between weather reporting points?
Unequal heating of the Earth’s surface
The wind at 5,000 feet AGL
Friction between the wind and the surface
The development of thermals depends upon
solar heating
Convective circulations patterns associated with sea breezes are caused by
cool, dense air moving inland from over the water
The boundary between two different air masses is referred to as a
front
One weather phenomenon which will always occur when flying across a front is a change in the
wind direction
One of the most easily recognized discontinuities across a front is?
A change in temperature
If there is thunderstorm activity in the vicinity of an airport at which you plan to land, which hazardous atmospheric phenomenon might be expected on the landing approach?
Wind-shear turbulence
A nonfrontal, narrow band active thunderstorms that often develop ahead of a cold front is known as a
squall line
What conditions are necessary for the formation of thunderstorms?
High humidity, lifting force, and unstable conditions.
During the life cycle of a thunderstorm, which stage is characterized predominately by downdrafts
Dissipating
Thunderstorms reach their greatest intensity during the
Mature stage
What feature is normally associated with the cumulus stage of a thunderstorm
continuous updraft
Which weather phenomenon signals the beginning of the mature stage of a thundrstorm?
Precipitation beginning to fall
Thunderstorms which generally produce the most intense hazard to aircraft are
squall line thunderstorms
Which weather phenomenon is always associated with a thunderstorm?
Lightning
The mature stage of a thunderstorm begins with
the start of precipitation
The destination airport has one runway, 8-26, and the wind is calm. The normal approach in calm wind is a left-hand pattern to runway 8. There is no other traffic at the airport. A thunderstorm about 6 miles west is beginning its mature stage, and rain is starting to reach the ground. The pilot decides to
delay departure until the thunderstorm has dissipated
You are avoiding a thunderstorm that is in your flightpath. You are over 20 miles from the cell: however, you are under the anvil of the cell. Is this a hazard
Yes, hail can be discharged from the anvil
One in-flight condition necessary for structural icing to form is
visible moisture
How will frost on the wings of an airplane affect takeoff performance
Frost will disrupt the smooth flow of air over the wing, adversely affecting its lifting capability
Which conditions result in the formation of frost
the temperature of the collecting surface is at or below the dewpoint of the adjacent air and the dewpoint is below freezing
How does frost affect the lifting surfaces of an airplane on takeoff
Frost may prevent the airplane from becoming airborne at normal takeoff speed
In which environment is aircraft structural ice most likely to have the highest accumulation rate?
Freezing rain
The presence of ice pellets at the surface is evidence that there
is a temperature inversion with freezing rain at a higher altitude
Why is frost considered hazardous to flight
Frost spoils the smooth flow of air over the wings, thereby decreasing lifting
An almond or lens-shaped cloud which appears stationary, but which may contain winds of 50 knots of more, is referred to as
a lenticular cloud
Crests of standing mountain waves may be marked by stationary, lens-shaped clouds known as
standing lenticular clouds
Possible mountain wave turbulence could be anticipated when winds of 40 knots or greater blow
across a mountain ridge, and the air is stable
Where does wind shear occur?
At all altitudes, in all directions
A pilot can expect a wind-shear zone in a temperature inversion whenever the wind speed at 2,000 to 4,000 feet above the surface is at least
25 knots
When may hazardous wind shear be expected?
In areas of low-level temperature inversion, frontal zones, and clear aur turbulence
If the temperature/dewpoint spread is small and decreasing, and the temperature is 62 F, what type weather is most likely to develop?
Fog or low clouds
What is meant by the term “dewpoint”?
The temperature to which air must be cooled to become saturated
The amount of water vapor which air can hold depends on the
air temperature
What are the processes by which moisture is added to unsaturated air?
Evaporation and sublimation
Clouds, fog, or dew will always form when
water vapor condenses
Low-level turbulence can occur and icing can become hazardous in which type of fog?
Steam fog
In which situation is advection fog most likely to form?
An air mass moving inland from the coast in winter.
What situation is most conductive to the formation of radiation fog?
Warm, moist air over low, flatland areas on clear, calm nights.
What types of fog depend upon wind in order to exist?
Advection fog and upslope fog
Clouds are divided into four families according to their
height range
The suffix “nimbus,” used in naming clouds means
a rain clopud
The conditions necessary for the formation of cumulonimbus clouds are a lifting action and
unstable, moist air
What clouds have the greatest turbulence?
Cumulonimbus
At approximately what altitude above the surface would the pilot expect the base of cumuliform clouds if the surface air temperature is 82 F and the dewpoint is 38 F
10,000 feet AGL
What cloud types would indicate convective turbulence?
Towering cumulus clouds
What is the approximate base of the cumulus clouds if the surface air temperature at 1,000 feet MSL is 70 F and the dewpoint is 48 F
6,000 feet MSL
Cumulus clouds often indicate
Possible turbulence
What is characteristic of stable air?
Stratiform clouds
When warm, moist, stable air flows upslope, it
Produces stratus type clouds
If unstable air mass is forced upward, what type clouds can be expected
Clouds with considerable vertical development and associated turbulence
What are characteristics of unstable air?
Turbulence and good surface visibility
A stable air mass is most likely to have which characteristic?
Poor surface visibility
Steady precipitation preceding a front is an indication of
Stratiform clouds with little or no turbulence
What are characteristics of a moist, unstable air mass?
Turbulence and good surface visibility
What measurement can be used to determine the stability of the atmosphere?
Actual lapse rate
The stability of an air mass can usually be determined by
Cloud types and the type if precipitation
What would decrease the stability of an air mass
Warming from below
What are the characteristics of an unstable atmosphere
A warm, humid air mass
Clouds with extensive vertical development over mountainous terrain are a sign of
an unstable air mass
What feature is associated with a temperature inversion?
A stable layer of air
The most frequent type of ground or surface-based temperature inversion is that which is produced by
Terrestrial radiation on a clear, relatively still night.
When there is a temperature inversion, you would expect to experience
an increase in temperature as altitude increases
Which weather conditions should be expected beneath a low-level temperature inversion layer when the relative humidity is high?
Smooth air, poor visibility, fog, haze, or low clouds
An increase in temperature with an altitude increase
is indication of an inversion
Temperature and radiation variations over land with a clear sky typically lead to
minimum temperature occurring after sunrise
