PPL Oral - Weather Theory Flashcards
(154 cards)
1
Q
What is the main driving force behind all weather on earth?
A
Uneven heating of the earths surface by the sun.
*Transfers of heat
2
Q
In what part of the atmosphere does most of the weather occur?
A
Troposphere
- Which is the first and lowest layer
- Goes as high as 48,000ft
3
Q
What is the atmosphere made of?
A
- Mostly
NITROGEN (78%) - and a little
OXYGEN (21%)
4
Q
In what part of the atmosphere does most of the weather occur?
A
Troposphere
- Which is the first and lowest layer
- Goes as high as 48,000ft
5
Q
What can you say in regards to how heat effects Land vs Water?
A
-Land heats up AND cools down FAST
-Water heats up AND cools down SLOW
6
Q
How does air flow around H & L pressure systems?
A
L = Counter-Clockwise (left) and UPWARDS (unstable)
H = Clockwise (right) and INWARDS (more stable)
7
Q
What kind of weather would you associate with a L pressure system?
A
Bad weather
- Rising air creates a lifting force leading to, precipitation, visible moisture.
- Air flows towards (winds) L pressure systems
- Low pressure systems contain warm air that wants to rise because it is less DENSE than cool air.
- As the air rises it cools to its dew point. Creating visible moisture. Especially when agitated by frontal activity.
8
Q
What kind of weather would you associate with a H pressure system?
A
Generally good weather
- Descending air, dissipating clouds
- air flows away (wind) from H pressure areas
9
Q
What is a Cold Front?
A
When a FAST Moving, COLD, DENSE and unstable air advances and replaces warmer air.
C\W
Why does this happen?
- Because winds may push Cold air into warm air, and warm air is Less Dense and will rise above the cold air.
10
Q
What is a Warm Front?
A
When a SLOW Moving Warm mass of air overtakes a cold mass of air.
W/C
Why does this happen?
- Winds may push the warm air into the cold air
- Because Warm air is LESS Dense than Cool air, the warm air begins to rise above the cold air.
- As it it rises the Warm Air will begin to cool to its dewpoint and if humidity is high, visible moisture will occur
11
Q
What can hold more Water Vapor, warm or cold air?
A
Warm air
Why?
- Because warm air is Less Dense and has more room to fit particles of water
- Warm moist air will rise more quickly because water vapor is lighter than air.
12
Q
Why does the air spin around L and H pressure systems?
A
Because of the Coriolis effect (rotation of the earth).
13
Q
How does air Travel in respect to H and L pressure systems?
A
Air travels from H TO L pressure systems.
Why?
- Because H pressure air is More DENSE than L pressure air.
-The H pressure air moves in to replace the rising L pressure air.
14
Q
Why does the air spin around L and H pressure systems?
A
Because of the Coriolis effect (rotation of the earth).
15
Q
Why does the air spin around L and H pressure systems?
A
Because of the Coriolis effect (rotation of the earth).
16
Q
How does air Travel in respect to H and L pressure systems?
A
Air travels from H TO L pressure systems.
Why?
- Because H pressure air is More DENSE than L pressure air.
-The H pressure air moves in to replace the rising L pressure air.
17
Q
Why does the air spin around L and H pressure systems?
A
Because of the Coriolis effect (rotation of the earth).
18
Q
How does air Travel in respect to H and L pressure systems?
A
Air travels from H TO L pressure systems.
Why?
- Because H pressure air is More DENSE than L pressure air.
-The H pressure air moves in to replace the rising L pressure air.
19
Q
Why does the air spin around L and H pressure systems?
A
Because of the Coriolis effect (rotation of the earth).
20
Q
What direction does air travel in respect to H and L pressure systems?
A
Air travels from H TO L pressure systems.
Why?
- Because H pressure air is More DENSE than L pressure air.
-The H pressure air moves in to replace the rising L pressure air.
21
Q
What happens when a Warm, Moist air mass reaches its Dewpoint?
A
Visible moisture will occur
22
Q
What is Dewpoint?
A
The temperature at which a mass of air needs to be cooled to reach 100% Relative Humidity
- At this point Water Condensation will occur
and droplets will form
23
Q
What is Relative Humidity?
A
The existing moisture in a mass of air compared to how much moisture it could hold.
- 100% Relative Humidity means that the air is completely saturated and any additional moisture will result in VISIBLE MOISTURE
24
Q
Which air mass will Cool Down more slowly.
Warm Moist air
OR
Cold Dry Air?
A
Warm Moist air will cool down at the slowest rate
Why?
- Because water resists changes in temperature.
- So Moist air will cool more slowly than Dry air
25
How can you calculate the height of clouds in AGL?
Take the difference between Temp and Dewpoint and divide it by the dew point/temp convergence rate of 2.5, then multiply it by 1,000.
EXAMPLE:
Temp: 22c
Dewp: 18c
4/2.5 = 1.6
Cloud Base = 1,600ft AGL
26
What is Atmospheric Stability?
The ability of an air mass to Resist Vertical Motion
27
What are the signs of a Front Passing through?
- A rapid change in WIND Direction
- A rapid change in PRESSURE
28
What are the characteristics of an Unstable Air Mass
CONS
- Cumulus clouds
- Vertical development
- Heavy rain
- Turbulent
PROS
- Good Visibility
29
What are the characteristics of a Stable Air Mass?
CONS
- Steady Precip
- Low Stratiform Clouds OR fog
- Low visibility
- Temperature Inversions
PROS
- Smooth air
30
What are the 3 ingredients that form a TS?
- Lifting Force
- Moisture (High Relative Humidity)
- Atmospheric Instability
31
Describe the different types of Lifting Forces that can form a TS?
1. Fronts
- Especially Cold fronts because they
produce the most Lifting Force
2. A Dry Line
3. Orographic lifting (terrain)
32
What is a Dry Line?
When a WARM, DRY air mass is pushed under a WARM MOIST air mass.
- When this occurs the Moist air is lighter due to water vapor and rises above the warm air, the rising will cause it to cool and reach its dewpoint, resulting in visible moisture
-Typically results in an INTENSE line TS in the great plains. (Squall line)
*usually happens when warm dry air from the western deserts meets the warm moist air from the gulf coast
*looks like an orange warm front on prog charts
33
What does a Dry Line Look like on a Prognostics Chart?
Like a an Orange Warm Front
34
What are the 3 Stages of a TS and describe their characteristics.
1. Developing (Cumulus) stage
- Updrafts
- Vertical Cumulus clouds
2. Mature Stage
- Heavy Rain
- Heavy updrafts/downdrafts
- Microbursts
3. Dissipating Stage
- Downdrafts
- Light rain
35
What are the 2 ways that Water Vapor may be Added to the atmosphere?
Evaporation and Sublimation (rare)
36
What is Evaporation?
The Sun HEATS up Water causing it to turn into VAPOR and be Added to the atmosphere
37
What are the 3 Categories of Clouds?
Low (up to 6,500ft)
- Stratus
- Stratocumulus
- NimboStratus
- Cumulus
- CumuloNimbus
Middle (up to 20,000ft)
- AltoStratus
- AltoCumulus
- NimboStratus
- CumuloNimbus
High (above 20,000ft)
- Cirrus
- CirroStratus
- CirroCumulus
38
Name all the Low Clouds
Low Clouds (up to 6,500ft)
- Stratocumulus
- Stratus
- Cumulus
- NimboStratus
- Cumulonimbus/Towering
Cumulonimbus
39
Name all the Middle Clouds
Middle Clouds (up to 20,000ft)
- AltoCumulus
- AltoStratus
- CumuloNimbus
40
Name all the High Clouds
High Clouds (above 20,000ft)
- Cirrus
- CirroStratus
- CirroCumulus
- CumuloNimbus/Towering CumuloNimbus
41
What is the most Hazardous type of storm to aircraft?
A Squall Line
42
What is a Squall Line?
A Long, Narrow Band of TS that often forms in front of a Cold Front.
- Single most dangerous weather hazard to aircraft
- Depicted on Prog Charts by Red Lines
with Red Dots
43
What is a good rule of thumb for how far to stay clear of a Thunderstorm or Extreme Radar Echo?
Stay 20 NM clear of the storm
Why?
- Because HAIL and gusts can exist for
miles around the TS
44
What is an Occluded Front?
When a COLD Front catches up to a Warm Front.
C W/Cool
- They are purple on Prog Charts
45
Explain how an Occluded Front works
Cold Air mass catches up to a Warm air mass that is already overtaking a COOL air mass.
- The Cold Front rapidly accelerates the rate of WX formation already happening on the Warm Front
46
What can be said about Warm Fronts vs Cold Fronts in respect to their speed?
Cold Fronts move faster than Warm Fronts
- Cold Front = More wind
47
What could be expected if you flew through the Middle Cloud known as Alto Stratus?
Moderate Turbulence and Moderate Icing
48
What could be expected if you flew through the Middle Cloud known as AltoCumulus?
Light Turbulence and Light Icing
49
What is Convection?
The tendency for Warmer, Lighter air to Rise.
50
Between a Warm Front and a Cold Front, which one would create worse weather?
A Cold Front
Why?
- Because Cold Fronts move fast and
can send the Warmer air Rising at a
rapid rate
51
What is a Stationary Front?
When Warm and Cold Fronts of equal strength meet.
- They look like a mixture between cold
and warm fronts on Prog Charts
- Stable air
- Bad weather for days
52
What are the 2 types of Occluded Fronts
Cold Front Occlusion
Warm Front Occlusion
53
Which type of Occluded Front is worse?
Warm Front Occlusion
Why?
- Because the Colder air under the Warm Front resists movement from the advancing Cold Front because the advancing Cold Front is not quite as cold as the Cold air that was already there (under the warm front).
- Advancing cold front = cold
- Already existing cold air = even COLDER
54
What is a Warm Front Occlusion?
Cold Front overtakes a Warm front that is overtaking even COLDER air
- Creates even worse weather than a standard Cold Front
- Advancing cold front = cold
- Already existing cold air = even COLDER
55
What is a Cold Front Occlusion
When a Cold Front overtakes a Warm Front and pushes both air masses forwards.
56
What is a Trough?
An elongated area of L pressure
- An area of rising air
- Expect bad weather
57
What kind of weather can be associated with a Cold Front?
Bad storms
- Towering Cumulus/CumuloNimbus
- Heavy rain
- TS
- Wind shear
- Drop in Temps
58
What kind of weather can be associated with a Warm Front?
Bad weather (but not as bad as a cold
front)
- Stratiform clouds
- Low clouds
- Rise in temps
59
What is a Ridge?
An elongated area of H Pressure
- Good weather due to downdrafts dissipating clouds
60
What is ISA?
International Standard Atmosphere
Temps - 15c (59f)
Pressure - 29.92 Hg
Altitude - Sea Level
61
What are Isobars?
Lines of equal pressure on weather charts
62
What does it mean if the Isobars are close together?
That means there is a STEEP pressure gradient (pressure changes quickly)
- It will be windy in these areas
63
Why do SURFACE winds flow ACROSS the Isobars instead of WITH the bars?
Because of Ground Friction
(Surface Friction)
64
At what is the standard lapse rate for Pressure as Altitude increases?
-1 inch Hg per 1,000ft of altitude gain
65
What is the standard Lapse Rate for Temperature as Altitude increases?
-2c per 1,000ft of altitude gain
66
What factor will primarily determine the type and extent of cloud development?
Atmospheric Stability
67
What can be said about the thickness of clouds during heavy rain?
They are at least 4,000ft thiccc
68
During preflight planning, what can you do to be sure you avoid icing?
1. Check frontal activity
- Ice is especially easy to form in H
pressure systems
2. Check cloud base and tops (PIREPs)
- Can you climb or descend to avoid
visible moisture?
3. Check Freezing levels - Avoid
4. Winds/Temps Aloft
5. Check Airmet Z
69
What is a Temperature Inversion
When the air at altitude is warmer than the air underneath it.
- Temperature has Increased at altitude
instead of decreasing
70
What are the 2 main types of Temperature Inversions?
1. Ground base TI
3. Frontal TI
71
What is a Ground Based Temperature Inversion?
This happens when the ground is cold and cools the air near it to a lower temperature than the air above it.
- The air above the cold layer near the
surface is now warmer and we have a
TI
72
When might you expect a Ground Based Temperature Inversion?
- Calm, COOL, stable Nights OR Mornings
with little wind
- When you can see a low layer of fog
73
Why do low layers of fog appear near Ground Based Temperature Inversions?
1. When the air that is cooled by the ground has MOISTURE in it, it may cool enough for it to reach its dewpoint and form visible moisture in the form of fog.
2. At this point, since the air has water vapor in it, it will try to rise. But it cant rise above the slightly warmer layer that is above it.
3. Now you have a low layer of fog
**Essentially durring radiation fog
74
Explain what is happening during a Frontal Temperature Inversion.
- Usually happens happens with slow
moving Warm Fronts
- The Warm air moves over and rises
above the Cold air
- TI will be closer to the ground nearest
to the Warm Front boundary
75
What dangerous hazard may be encountered near a Ground Based Temperature Inversion?
LLWS!
76
What is WindShear?
A rapid change in wind speed or direction at different altitudes
77
What is so dangerous about WindShear?
Because it can cause..
1. Rapid decrease or increase in
Airspeed low to the ground rather
unexpectedly
2. Can significantly blow us off course or
cause unexpected cross winds when
landing
78
When are the 3 most likely times you can expect LLWS?
1. Near Frontal activity
- Especially with steep pressure
gradients
- Especially when the temp difference
on either side of the front is > 5c
2. Near Thunderstorms
- Microbursts
- Can be expected as far out as 20nm
from the storm
3. When a Temperature Inversion is
present
79
What are the 2 types of WindShear in relation to aircraft performance?
1. Performance Decreasing Windshear
- Happens when High winds rapidly
DECREASE.
- Carry extra airspeed with you on
final if WS is expected
2. Performance Increasing Windshear
- Happens when the winds rapidly
INCREASE
- Watch your airspeed, make sure you
don't exceed Vno
80
How can you tell if WindShear is present near a Ground Based Temperature Inversion?
If the winds aloft above the inversion are greater than 25 Kts.
81
WindShear Scenario:
METAR:
Winds at surface = 10kts
*WS010/18040
What's going on here?
WS010/18040 = Windshear at 1,000ft AGL, 180 at 40kts
Here's what is going on
- Winds at 1,000ft are 40kts. Check surface winds to see difference between surface and 1000ft.
- This is Performance DECREASING
Windshear
What should you do?
- Carry an extra 30kts with you until about 500ft AGL
82
What is an Embeded Thunderstorm?
A TS hidden within other clouds
83
How can you make sure your landings are smooth even in Gusty conditions?
Add a Gust factor to your landing speed
- Take half of the difference between
the winds and the gusts and add it to
your airspeed on final
Winds 10kts
Gusts 20kts
- Add 5kts to your approach speed
(82kts with flaps T/O)
84
If there was a thunderstorm near your arrival airport, what would you do?
**DIVERT
BUT, if you HAD to land
- Pick the RWY farthest away from the
storm.
Why?
- Because winds flow out of storms and you want to land with a Headwind
- Especially if it begins to gust
85
What is a hazard you need to be aware of when flying near Mountains?
Mountain Wave Turbulence
86
What is Mountain Wave Turbulence?
Winds in excess of 25kts flowing over (perpendicular) a mountain ridge
Windward Side -> A -> Leeward Side
Turbulence can be expected on the Leeward side
87
What are some signs that Mountain Wave Turbulence is present?
- Winds in excess of 25kts flowing over (perpendicular) a mountain ridge
- Standing Lenticular Clouds over the top
of a mountain
- Lines of Rotor clouds on the Leeward
Side
88
What are the different types of fog?
1. Ground/Radiation Fog
2. Upslope Fog
3. Advection Fog
4. Steam Fog
89
Explain Ground/Radiation Fog
The cold ground Cools the moist/humid air above it to its dewpoint, causing fog to form. (provided there is high moisture and low winds)
90
Explain Upslope Fog
A light wind pushes Moist air up a slope until it cools to its dewpoint and condenses into fog.
91
Explain Advection Fog
Occurs when Warm Moist air flows over a cold surface and is cooled to its dewpoint
92
Explain Steam Fog
Occurs when evaporation from a warmer body of water lifts moisture into colder air, allowing it to reach its dewpoint and fog forms.
93
What is necessary for Structural Icing to occur?
- Visible moisture
- Freezing temperatures on the COLLECTING SURFACE
94
What are the 2 main categories of Aircraft Icing?
1. Structural
2. Induction (air intake, carb ice)
95
What are the 3 types of Structural Icing?
1. Clear Ice
2. Rime Ice
3. Mixed Ice
96
What is Clear Structural Icing?
Clear ice that slowly freezes as it moves across the surface of the wing
- Formed by large water droplets
97
What is Rime Structural Icing?
A milky, opaque, rough looking ice that form in bulk on the leading edge
- formed by smaller water droplets
98
What is Mixed Structural Icing
A mix between Rime (worst aerodynamics) and Clear (heaviest)
99
Why is ice on our aircraft a bad thing?
1. Changes the shape of the wing (less
lift)
2. Creates more Drag
3. Adds weight
4. It will increase your stall speed!
5. Can clog sensors like our Pitot or
Static ports
100
Under what conditions can you expect Carburetor Icing?
When..
1. Relative Humidity is high
2. Temps between -7c - 21c
*BUT it CAN occur in higher temps than these!
101
What are some indications of Carburetor Icing?
1. Engine running rough
2. Loss of RPM (fixed pitch) OR Manifold
Pressure (constant speed prop)
102
If you suspect Carburetor Icing how can you check to be sure?
1. Turn on carb heat (RPM and Man Pressure
will drop further)
2. Wait a bit and IF RPM/Man Pressure
increases, (ice melting) you have carb icing!
103
If you suspect induction icing in the DA 40 what should you do?
1. Open alternate air
2. Pitot heat on
3. Increase power to prevent ice build up on
prop
4. Descend, and or turn around for warmer
air
104
What would be an indication for Induction Icing in the DA 40?
Loss of power
105
Is frost dangerous to aircraft?
Yes.
Why?
1. Its enough to disrupt smooth airflow over the wing resulting in a LOSS of LIFT
2. It can increase your stall speed
| FAR 91.527 prohibits T/O with frost, ice, or snow on the aircraft
106
What is needed for fog to form?
- Low temp/dewpoint spread
- High relative humidity (moisture)
- Stable air
- Calm winds (calm, not necessarily zero winds)
107
What are some conditions that contribute to High Density Altitude?
- High elevations
- Higher than standard temperature
- Lower than Standard atmospheric pressure
- High humidity (moist air. Decreases air density)
..Or a combination of these factors
108
What are some conditions that contribute to Low Density Altitude?
- Low elevation
- Lower than standard temp
- Higher than standard pressure
- Low humidity (dry air. Increases density)
..Or a combination of these
109
What are the weather minimums to obtain a special VFR clearance?
FAR 91.157
1. 1 SM vis
2. Clear of Clouds
110
Why is Low-Level Wind Sheer often associated with the passage of Fronts?
Due to the relatively rapid change in wind direction near Fronts
111
Where would WindShear be expected along a passing Warm Front?
- AHEAD of the Warm Front
- Within 6hrs of its passing
- Below 5,000ft
112
How long does a Microburst typically last?
Up to 15 mins
113
What are all the conditions that are conducive to Low Level Wind Shear?
- Passing fronts
- Thunderstorms
- Temperature Inversions with strong upper level winds in excess of 25kts
114
When is an aircraft most likely to be struck by lightening?
When the OAT is between -5c and +5c
115
Under what conditions should you be very wary of icing?
- Temps from -20c to +5c
- Flying in visible moisture
116
What determines the stability of an atmosphere?
The Adiabatic Lapse rate (temperature lapse rate)
Rapid cooling as altitude increases will result in an unstable atmosphere, while normal to slow cooling will result in a stable atmosphere.
*average temperature lapse rate is -2c per 1,000ft altitude gain
117
In regards to icing, what meteorological information should pilots be aware of?
AC-91-74
1. Frontal locations
2. Cloud layers
3. Freezing level
4. Temperature and Pressure (low pressure is conducive to icing)
5. Precipitation
118
Is icing more likely to form near areas of Low or High Pressure?
AC-91-74
Low pressure
119
What are the reporting categories for aircraft icing?
AIM 7-1-19
1. Trace
2. Light
3. Moderate
4. Severe
120
What effect does aircraft icing have on performance? ( 5 things, get them all right)
AIM 7-1-19
1. Thrust is reduced
2. Drag Increases
3. Lift decreases
4. Weight increases
5. Result: Stall speed increases
*these effects are cumulative
121
Where can icing be expected?
AIM 7-1-19
Anywhere visible moisture or precipitation is present and the OTA is +2c to -10c
**but can occur at +5c to -20c**
122
What should you do if you encounter aircraft icing?
AIM 7-1-19
1. Leave the area of visible moisture by turning around
2. Leave the area of near freezing temps by descending OR climbing (temp inversion)
123
What should you do after you have successfully left an area where icing conditions have been encountered? (2 things)
AIM 7-1-19
1. Let ATC know the type and severity of icing encountered
2. Obtain an amended clearance with a new route away from the icing, or DIVERT if needed.
124
What is Trace icing, what is its rate of accumulation, and what action should be taken?
AIM 7-1-19
1. Trace icing is when icing first becomes noticeable
2. 1/4 inch per hour on outer wing
3. Consider exiting icing conditions before they worsen
125
What is Light icing, at what rate does it accumulate, and what action should be taken?
AIM 7-1-19
1. Light icing requires the occasional cycling of deicing systems
2. 1/4 to 1 inch accumulation per hour
3. Exit icing conditions
126
What is Moderate icing, at what rate does it accumulate, and what action should be taken?
1. Moderate icing requires the FREQUENT cycling of deicing systems
2. 1-3 inches per hour
3. Exit icing conditions ASAP
127
What is Severe Icing, at what rate does it accumulate, and what action should be taken?
AIM 7-1-19
1. Severe icing is occurring when ice protection systems fail to remove the ice and ice accumulates in areas normally not prone to icing
2. More than 3 inches per hour
3. Exit IMMEDIATELY, by regulation
128
What is Clear Ice?
1 . Glossy, translucent ice formed by the relatively slow freezing of large droplets.
2. Clear ice forms as the droplets slowly freeze as they roll backwards on the surface of the aircraft
3. Can forms horns that disrupt airflow
*** MOST DANGEROUS ***
*Usually form in warmer temps than Rime ice
128
What is Rime Ice?
Rough, milky, ice formed by the rapid freezing of supercooled droplets upon impact.
**Most common type.
**Rime ice gets its milky appearance from air bubbles trapped in-between the ice as it rapidly freezes
128
When are you most likely to encounter Rime Ice?
1. Usually forms in colder temps
2. In stable conditions like Stratus clouds
129
What is Mixed Icing?
1. A mix of Clear and Rime ice that forms when flying through varying conditions of cold, and moisture.
2. Can form horns
130
What is the most dangerous type of icing to encounter and why?
Clear Ice
- Heavy, adds weight
- Ice can accumulate behind where the de-icing equipment is installed
- Hard to see
- Forms horns that further disrupt the airflow
131
What are Super Cooled Water Droplets?
1. Pure water that does not freeze until -20c, due to surface tension
2. They will freeze instantly if sufficiently disturbed (like by an aircraft flying into them)
132
What are the two main categories of Aircraft Icing?
1. Induction icing (engine)
2. Airframe icing
133
At what temperatures will it be too cold for icing to occur and why?
1. Usually less than -20c
2. Because most water content is already frozen as ice crystals
134
At what temperatures are you mostly likely to encounter Rime, Clear, and Mixed icing respectively?
Rime = Temps less than -15c
Clear = 0c to -10c
Mixed = -10c to -15c
135
In Stratiform type clouds, what type of icing can you expect, and at what intensity, and what can be said about the thickness of the icing layer?
1. Rime and Mixed
2. Trace and light
3. Generally, the icing layer in a Stratiform cloud is about 3,000-4,000ft thick, so climbing above it is an option.
136
In Cumuliform type clouds, what type of icing can you expect, and at what intensity, and where will the worst icing be?
1. All types of icing
2. All intensities
3. Worst icing will occur near the top of the Cumuliform formation
137
What is the worst weather phenomenon to encounter in regards to aircraft icing?
Freezing rain
138
In what scenario would it be possible to achieve multiple freezing levels over one area?
AC-91-74
A temperature inversion
139
What are some good preflight planning things to consider when the possibility of encountering icing is present?
AC-91-74
1. Pre-determine exit strategies, will a climb or descent, or turn-around be most appropriate given the conditions?
2.Extra fuel may be needed due to the drag that icing may cause or due to drag from de-icing systems
3. When choosing alternate airports, remember that icing will require a higher approach speed and therefore, a longer RWY!
140
How can you visually identify the Jet Stream (and possible Clear Air Turbulence)?
Long streaks of Cirrus clouds
| Shephard Air: Commercial question
141
Why would you expect lower aircraft performance when Relative Humidity is high?
Because water vapor is LESS DENSE than air, and since there is a lot of water in the air durring High Relative Humidity conditions, the air also becomes LESS DENSE due to the excess moisture.
142
When are convective currents most active?
Warm Summer afternoons when winds are Light
| Aviation Weather Handbook
143
What two conditions would cause an air mass to become unstable?
High Temps & High Humidity
144
You approach a mountanous area at 10,000ft from the East with winds 50kts from the West, you also see flat, lense shaped clouds ahead. What is this an indication of?
Very strong Mountain Wave Turbulence.
Avoid
145
Your weather investigating has revealed that there is High Humidity, Higher than average Lapse Rate, & Turbulent conditions.
What do these signs point to?
The possibility for..
* 1. Thunderstorm activity
* 2. Unstable air
146
When are you most likely to encounter Clear Air Turbulence (CAT)?
Between 20,000 and 50,000ft, in a cloud-free area
| Aviation Weather Handbook
147
What weather conditions indicate the passage of a cold front?
High Dew Point
Falling pressure
| PHAK 12-20
148
What should you do if you encounter moderate or severe turbulence?
Slow to Manuevering Speed (Va) and maintain wings level
| You should accept altitude and speed deviations
149
What are two clues that Windshear associated with frontal activity may be present?
1. The temp difference at the surface on either side of the front is greater than 10c
2. The front is moving at a speed of 30kts or more
| Source: Boldmethod
## Footnote
https://www.boldmethod.com/blog/lists/2023/09/four-most-common-sources-of-wind-shear-at-low-altitude/
150
What is the difference between Freezing Drizzle & Freezing Rain?
Drizzle is rain with droplets .02 inch in diameter or smaller, Rain will be larger than .02 inch
* The freezing aspect refers to water existing in liquid form at or below freezing temperatures.
* The Freezing Drizzle/Rain will form ice on contact with a surface
151
Does flying through snow count as 'known icing'?
It depends:
* Flight in light, ***DRY*** snow, with temps below -5c offer low icing risk
* Wet snow in temps from -0c to -5c, OR flight into clouds while its snowing will offer greater icing risk
| Source: Boldmethod
## Footnote
Source: https://www.boldmethod.com/learn-to-fly/weather/is-flying-through-snow-considered-known-icing-conditions-flight-winter-imc/#:~:text=In%202006%2C%20the%20FAA%20published,determinative%20factor%20in%20this%20definition.
152
At what point does Fog bcome Clouds?
1. Fog are clouds below 50ft AGL, once the fog lifts above 50ft, it is considered a cloud (Weather.gov)
2. However, a METAR will report fog when visibility is reduced to 5/8 statute mile or less (AIM Ch 7)
| Source: Weather.gov, AIM Ch 7
## Footnote
https://www.weather.gov/source/zhu/ZHU_Training_Page/clouds/cloud_development/clouds.htm#:~:text=There%20is%20no%20difference%20between,radiation%20fog%20and%20advection%20fog.
