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Weather Hazards
Chapter 9, Section B
Thunderstorms
• Conditions
– Unstable air
– Lifting action
– High moisture content
• Stages
– Cumulus stage
– Dissipating stage
Mature stage
Hazards
• Embedded thunderstorms may be
obscured by cloud layers
• Wind shear can be found on all
sides as well as directly under it
• Greatest intensity during mature
stage, which is signaled by
precipitation at the surface
Types of Thunderstorms
• Airmass thunderstorms are usually
isolated or scattered over a large area
• Frontal thunderstorms associated with
frontal activity
• Squall line is a narrow band of active
thunderstorms normally containing
severe weather
Hazards
• Lightning is always associated with
thunderstorms
• Hail is often associated with
cumulonimbus clouds but can be found
in clear area several miles from the
cloud
• Funnel clouds - tornado or waterspout
Thunderstorm Avoidance
• Use weather radar to avoid
thunderstorms
• Avoid echoes by at least 20 miles Do not fly between if less than 40
miles apart
• Weather radar does not pick up fog
or clouds
Turbulence
• Low-level Turbulence below
15,000 feet consists of
– Mechanical Turbulence
– Convective Turbulence
– Frontal Turbulence
– Wake Turbulence
Mechanical Turbulence
• Wind forms eddies as it blows
around hanger, stands of trees or
other obstructions
Convective Turbulence
• Thermal Turbulence is a daytime
phenomena which occurs over land
in fair weather
• Capping stable layer begins at the
top of the convective layer. It can
be identified by a layer of cumulus
clouds, haze or dust
Frontal Turbulence
• Occurs in the narrow zone just
ahead of a fast-moving cold front
Wake Turbulence
• Wingtip vortices occurs when an
airplane generates lift
• They can exceed the roll rate of an
aircraft
• Greatest when an aircraft is heavy,
slow and clean
Wingtip Vortices
• Tend to sink below the flight path
of the generating aircraft
• Most hazardous during light,
quartering tailwinds
• Land beyond where a large aircraft
has touched down
Wingtip Vortices
• Lift off before the point a large
aircraft departing in from of you
lifted off climb out above his flight
path or turn upwind
• Helicopters in forward flight
produce wingtip vortices like
circulation of air
Clear Air Turbulence
• Turbulence above 15,000 feet AGL
not associated with cumuliform
cloudiness is reported as CAT
• CAT is common in a upper trough
on the polar side of the jet stream
Jet Stream
• A curving jet stream associated
with a deep low pressure trough
can be expected to cause great
turbulence
• Jet stream can sometime be
identified by long streaks of cirrus
clouds
Mountain Wave Turbulence
• Greatest turbulence occurs
approaching the lee side of a
mountain range in strong headwinds
• Standing lenticular and rotor clouds
indicate the possibility of strong
turbulence
Reporting Turbulence
• Light - slight erratic changes in
altitude or attitude
• Moderate - aircraft remains in
positive control
• Severe - large abrupt changes in
altitude and attitude and may be
momentarily out of control
Wind Shear
• Sudden, drastic shift in wind speed
and/or direction over a short distance
• May be associated with a strong lowlevel temperature inversion, a jet
stream, a thunderstorm or a frontal
zone
Microbursts
• Intense, localized downdrafts seldom
lasting longer than 15 minutes
• Downdrafts can be as strong as 6,000
feet per minute
• Performance changes drastically as
an aircraft flies through a microburst
Low-Level Wind Shear Systems
• LLWAS - system of anemometers
compares wind speed at several
locations around the airport
• Terminal Doppler Weather Radar
provide a clearer, more detailed
picture of a thunderstorm
• Visual - Virga
Restrictions to Visibility
• Fog, haze, smoke, smog and dust
• Fog requires moisture and
condensation nuclei
• Industrial areas produce much fog
since they have more condensation
nuclei
Fog
• Radiation Fog - ground fog - forms
over fairly flat land on clear, calm
nights
• Advection fog- forms near coastal
areas when moist air moves over
colder ground or water
Fog
• Upslope fog forms when moist stable
air is forced up a sloping land mass
• Steam fog occurs as cool air moves
over warmer water
• Precipitation-induced fog forms when
warm rain falls through a layer of
cooler air near the surface
Fog
• Ice fog occurs in cold weather
when the temperature is much
below freezing and water vapor
sublimates directly as ice crystals
Icing
• Freezing rain is most likely to have
the highest rate of accumulation
• Ice, snow or frost having the
thickness and roughness of
sandpaper and reduce lift by 30%
and increase drag by 40%
Cold Weather Operations
• Preheat the cabin as well as the
engine, but not at KSU
• Warm crankcase breather lines
since they may be clogged by ice
from vapors that have condensed
and subsequently frozen
338.
I27
COM
Fog produced by frontal activity is a result
of saturation due to
A. evaporation of precipitation.
B. adiabatic cooling.
C. nocturnal cooling.
338.
I27
COM
Fog produced by frontal activity is a result
of saturation due to
A. evaporation of precipitation.
363.
I31
COM
A situation most conducive to the formation
of advection fog is
A. a light breeze moving colder air over a
water surface.
B. an air mass moving inland from the
coastline during the winter.
C. a warm, moist air mass settling over a
cool surface under no-wind conditions.
363.
I31
COM
A situation most conducive to the formation
of advection fog is
B. an air mass moving inland from the
coastline during the winter.
364.
I31
COM
Advection fog has drifted over a coastal
airport during the day. What may tend to
dissipate or lift this fog into low stratus
clouds?
A. Wind 15 knots or stronger.
B. Nighttime cooling.
C. Surface radiation.
364.
I31
COM
Advection fog has drifted over a coastal
airport during the day. What may tend to
dissipate or lift this fog into low stratus
clouds?
A. Wind 15 knots or stronger.
365.
I31
COM
In what ways do advection fog, radiation fog, and steam fog
differ in their formation or location?
A. Steam fog forms from moist air moving over a colder
surface; advection fog requires cold air over a warmer surface;
radiation fog is produced by radiational cooling of the ground.
B. Advection fog deepens as windspeed increases up to 20
knots; steam fog requires calm or very light wind; radiation
fog forms when the ground or water cools the air by radiation.
C. Radiation fog is restricted to land areas; advection fog is
most common along coastal areas; steam fog forms over a
water surface.
365.
I31
COM
In what ways do advection fog, radiation fog, and steam fog
differ in their formation or location?
C. Radiation fog is restricted to land areas; advection fog is
most common along coastal areas; steam fog forms over a
water surface.
366.
I31
COM
With respect to advection fog, which statement
is true?
A. It can appear suddenly during day or night,
and it is more persistent than radiation fog.
B. It forms almost exclusively at night or near
daybreak.
C. It is slow to develop, and dissipates quite
rapidly.
366.
I31
COM
With respect to advection fog, which statement
is true?
A. It can appear suddenly during day or night,
and it is more persistent than radiation fog.