7: Aviation Weather |
While flying cross-country in the Northern Hemisphere, you experience a continuous left crosswind which is associated with a major wind system. This indicates that you
are flying toward an area of generally unfavorable weather conditions.
One of the most dangerous features of mountain waves is the turbulent areas in and
below rotor clouds.
The Low Level Wind Shear Alert System (LLWAS) provides wind data and software process to detect the presence of a
change in wind direction and/or speed within a very short distance above the airport.
Turbulence that is encountered above 15,000 feet AGL not associated with cumuliform cloudiness, including thunderstorms, should be reported as
clear air turbulence.
With regard to windflow patterns shown on surface analysis charts; when the isobars are
close together, the pressure gradient force is greater and wind velocities are stronger.
A moist, unstable air mass is characterized by
cumuliform clouds and showery precipitation.
Hail is most likely to be associated with
cumulonimbus clouds.
Which is true regarding actual air temperature and dew point temperature spread? The temperature spread
decreases as the relative humidity increases.
Moisture is added to a parcel of air by
evaporation and sublimation.
Fog produced by frontal activity is a result of saturation due to
evaporation of precipitation.
Ice pellets encountered during flight are normally evidence that
freezing rain exists at higher altitude.
The greatest threats to an aircraft operating in the vicinity of thunderstorms are:
hail and turbulence.
A common location of clear air turbulence is
in an upper trough on the polar side of a jet stream.
Hazardous wind shear is commonly encountered
in areas of temperature inversion and near thunderstorms.
GIVEN: Winds at 3,000 feet AGL 30 kts Surface winds Calm While on approach for landing, under clear skies with convective turbulence a few hours after sunrise, one should
increase approach airspeed slightly above normal to avoid stalling.
Which is true regarding a cold front occlusion? The air ahead of the warm front
is warmer than the air behind the overtaking cold front.
Convective circulation patterns associated with sea breezes are caused by
land absorbing and radiating heat faster than the water.
When flying low over hilly terrain, ridges, or mountain ranges, the greatest potential danger from turbulent air currents will usually be encountered on the
leeward side when flying into the wind.
When flying into a low-pressure area in the Northern Hemisphere, the wind direction and velocity will be from the
left and increasing.
The difference found by subtracting the temperature of a parcel of air theoretically lifted from the surface to 500 millibars and the existing temperature at 500 millibars is called the
lifted index.
A pilot reporting turbulence that momentarily causes slight, erratic changes in altitude and/or attitude should report it as
light turbulence.
Convective currents are most active on warm summer afternoons when winds are
light.
The jet stream and associated clear air turbulence can sometimes be visually identified in flight by
long streaks of cirrus clouds.
When turbulence causes changes in altitude and/or attitude, but aircraft control remains positive, that should be reported as
moderate.
Which situation would most likely result in freezing precipitation? Rain falling from air which has a temperature of
more than 32°F into air having a temperature of 32°F or less.
A strong wind shear can be expected
on the low-pressure side of a jetstream core where the speed at the core is stronger than 110 knots.
The general circulation of air associated with a high-pressure area in the Northern Hemisphere is
outward, downward, and clockwise.
During an approach, the most important and most easily recognized means of being alerted to possible wind shear is monitoring the
power and vertical velocity required to remain on the proper glidepath.
In the Northern Hemisphere, the wind is deflected to the
right by Coriolis force.
During the winter months in the middle latitudes, the jet stream shifts toward the
south and speed increases.
The most severe weather conditions, such as destructive winds, heavy hail, and tornadoes, are generally associated with
squall lines.
The formation of either predominantly stratiform or predominantly cumuliform clouds is dependent upon the
stability of the air being lifted.
The conditions most favorable to wave formation over mountainous areas are a layer of
stable air at mountaintop altitude and a wind of at least 20 knots blowing across the ridge.
The conditions necessary for the formation of stratiform clouds are a lifting action and
stable, moist air.
If clouds form as a result of very stable, moist air being forced to ascend a mountain slope, the clouds will be
stratus type with little vertical development and little or no turbulence.
Virga is best described as
streamers of precipitation trailing beneath clouds which evaporate before reaching the ground.
Low-level wind shear may occur when
there is a low-level temperature inversion with strong winds above the inversion.
The conditions necessary for the formation of cumulonimbus clouds are a lifting action and
unstable, moist air.
The presence of standing lenticular altocumulus clouds is a good indication of
very strong turbulence.
On Surface Analysis Charts, widely spaced isobars indicate a
weak pressure gradient.
The strength and location of the jet stream is normally
weaker and farther north in the summer.
What are the standard temperature and pressure values for sea level?
15°C and 29.92" Hg.
What minimum distance should exist between intense radar echoes before any attempt is made to fly between these thunderstorms?
40 miles.
The minimum vertical wind shear value critical for probable moderate or greater turbulence is
6 knots per 1,000 feet.
What is the approximate base of the cumulus clouds if the temperature at 2,000 feet MSL is 10°C and the dew point is 1°C?
6,000 feet MSL.
Which type of jetstream can be expected to cause the greater turbulence?
A curving jetstream associated with a deep low-pressure trough.
Which is true with respect to a high- or low-pressure system?
A high-pressure area or ridge is an area of descending air.
Why does the wind have a tendency to flow parallel to the isobars above the friction level?
Coriolis force tends to counterbalance the horizontal pressure gradient.
What prevents air from flowing directly from high-pressure areas to low-pressure areas?
Coriolis force.
Which are characteristics of a cold air mass moving over a warm surface?
Cumuliform clouds, turbulence, and good visibility.
What visible signs indicate extreme turbulence in thunderstorms?
Cumulonimbus clouds, very frequent lightning, and roll clouds.
During the life cycle of a thunderstorm, which stage is characterized predominately by downdrafts?
Dissipating.
If a temperature inversion is encountered immediately after takeoff or during an approach to a landing, a potential hazard exists due to
wind shear.
What is the standard temperature at 20,000 feet?
-25°C.
What is the standard temperature at 10,000 feet?
-5°C.
If airborne radar is indicating an extremely intense thunderstorm echo, this thunderstorm should be avoided by a distance of at least
20 miles.
What is the standard temperature at 6,500 feet?
2°C.
Which is true regarding high- or low-pressure systems?
A low-pressure area or trough is an area of rising air.
Which feature is associated with the tropopause?
Abrupt change in temperature lapse rate.
Thunderstorms identified as severe or giving an intense radar echo should be avoided by what distance?
At least 20 miles.
Which conditions are favorable for the formation of a surface based temperature inversion?
Clear, cool nights with calm or light wind.
Which is a characteristic typical of a stable air mass?
Continuous precipitation.
What feature is normally associated with the cumulus stage of a thunderstorm?
Continuous updraft.
Which is true regarding the development of convective circulation?
Cool air must sink to force the warm air upward.
Which would increase the stability of an air mass?
Cooling from below.
What is indicated if ice pellets are encountered at 8,000 feet?
Freezing rain at higher altitude.
Which statement is true concerning the hazards of hail?
Hailstones may be encountered in clear air several miles from a thunderstorm.
With respect to advection fog, which statement is true?
It can appear suddenly during day or night, and it is more persistent than radiation fog.
What is an important characteristic of wind shear?
It can be present at any level and can exist in both a horizontal and vertical direction.
Of the following, which is accurate regarding turbulence associated with thunderstorms?
Outside the cloud, shear turbulence can be encountered 20 miles laterally from a severe storm.
What are the characteristics of stable air?
Poor visibility; steady precipitation; stratus clouds.
Which in-flight hazard is most commonly associated with warm fronts?
Precipitation-induced fog.
What causes wind?
Pressure differences.
In what ways do advection fog, radiation fog, and steam fog differ in their formation or location?
Radiation fog is restricted to land areas; advection fog is most common along coastal areas; steam fog forms over a water surface.
Which is a characteristic of stable air?
Restricted visibility.
When an air mass is stable, which of these conditions is most likely to exist?
Smoke, dust, haze, etc., concentrated at the lower levels with resulting poor visibility.
What is a characteristic of stable air?
Stratiform clouds.
What type weather can one expect from moist, unstable air, and very warm surface temperature?
Strong updrafts and cumulonimbus clouds.
When conditionally unstable air with high-moisture content and very warm surface temperature is forecast, one can expect what type of weather?
Strong updrafts and cumulonimbus clouds.
What lifts advection fog into low stratus clouds?
Surface winds of approximately 15 knots or stronger.
From which measurement of the atmosphere can stability be determined?
The ambient lapse rate.
Select the true statement pertaining to the life cycle of a thunderstorm.
The beginning of rain at the Earth's surface indicates the mature stage of the thunderstorm.
Which is true regarding the use of airborne weather-avoidance radar for the recognition of certain weather conditions?
The radarscope provides no assurance of avoiding instrument weather conditions.
What determines the structure or type of clouds which will form as a result of air being forced to ascend?
The stability of the air before lifting occurs.
Which weather phenomenon signals the beginning of the mature stage of a thunderstorm?
The start of rain.
Ice pellets encountered during flight normally are evidence that
a warm front is about to pass.
Which statement is true regarding squall lines?
They are nonfrontal and often contain severe, steady-state thunderstorms.
Which statement is true concerning squall lines?
They offer the most intense weather hazards to aircraft.
Which cloud types would indicate convective turbulence?
Towering cumulus clouds.
Which combination of weather-producing variables would likely result in cumuliform-type clouds, good visibility, and showery rain?
Unstable, moist air and orographic lifting.
Which would decrease the stability of an air mass?
Warming from below.
Advection fog has drifted over a coastal airport during the day. What may tend to dissipate or lift this fog into low stratus clouds?
Wind 15 knots or stronger.
A situation most conducive to the formation of advection fog is
an air mass moving inland from the coastline during the winter.
The wind system associated with a low-pressure area in the Northern Hemisphere is
a cyclone and is caused by Coriolis force.
Every physical process of weather is accompanied by or is the result of
a heat exchange.
During departure under conditions of suspected low-level wind shear, a sudden decrease in headwind will cause
a loss in airspeed equal to the decrease in wind velocity.
