Aviation Weather Flashcards
bIn what ways does weather affect aviators?
Reduces visibility
Create turbulance
Reduces A/C performance
Components of Dry Air
78 % Nitrogen
21 % Oxygen
1 % Noble Gases
Natural Air
Dry Air + Condensation Nuclei + Water Vapor
Atmosphoric Layers
Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere
Three Cell Theory of Atmospheric Circulation
Reasons
Uneven Heating from the sun
Tilt of Earth
Coriolos force
What two additional ingredients does natural air have that dry air does not?
Water vapor, condensation nuclei
Between the 30 - 60 degree N latitude is primarily where the US is located. What is the prevailing wind direction?
Westerly
In which layer of the atmosphere does weather occur?
Tropossphere
Air Mass Classification
Water Vapor Content
c
m
Continental Air Mass (Dry Air)
Maritime Air Mass (Moist Air)
Air Mass Classification
Temperature
A
P
T
E
Arctic Air Mass (70 - 90 degree)
Polar Air Mass (40 - 60 degree)
Tropical Air Mass (10 - 30 degree)
Equatorial Air Mass (0 - 10 degree)
What is a cP
Continental Polar (Dry from 40 - 60 degree)
4 Methods of Heat Transfer
Radiation, Conduction, Convection (vertical), Advection (horizontal)
Temperature Inversion
An altitude where there is warmer air above colder air
Temperature Inversion
An altitude where there is warmer air above colder air
By radiation: Ground radiates heat and cools lowest air layer by conduction. Air layer above is hotter than Ground layer. Clear sky means cold night (Clouds prevents this inversion)
Frontal: Shift of air masses with different temperature below or above each other
Explain the difference between convection and advection
Convection is vertical
Advection is horizontal
In late evening, a thick layer of clouds have moved over your airfield. Will noctural radiation occur?
No. The clouds prevent an inversion from happening by keeping the warmer air near the surface
Atmospheric Pressure is…
… the force excerted by the weight of a column of air per unit area
Standard Day Pressure
29.92 Hg
1013.2 hP or mb
Pressure Systems
High
Sinking air near center
Divergence
Light to moderate wind
Usually no turbulance
Visibility is good, except morning haze, fog
Flying conditions - good
Pressure Systems
Low (Cyclone)
Lifting air near center of low
Convergence
Moderate to strong wind
Turbulance
Visibilty limited by clouds, fog, precipation
All fronts are low pressures
Flight conditions - poor
Isobars
connecting points whith the same pressure, 4 mb apart
Wind directions
High - Clockwise Away from it
Low - Counterclockwise to it
Pressure Gradient Force
Isobar spacing
Isobars closely spaced: strong or steep pressure gradient, moderate to strong wind
vice versa
Pressure Gradient Force
Force exerted by change in pressure per unit of horizontal distance
Coriolis Force
An apparant deflective force resulting from the Earths rotation
Changes in Moisture
Evaporation
Condensation
Fusion (freezing)
Deposition (Gas to Soldi)
Sublimation (Solid to Gas)
Melting
Adiabatic Process
Heating and Cooling due to Compression and Expanding
Types of Clouds
Cumulus
Stratus
Families of Clouds
Low
Middle
High
Low Clouds
Base within 6.500 AGL
Cumulus - CU
Stratus - ST
Stratocumulus - SC
Cumulonimbus - CB
Middle Clouds
Base of Clouds between 6.500 AGL - 20000 AGL
Altostratus - AS
Altocumulus - AC
Nimbostratus - NS
Characteristics
Stratocumulus
Inbetween Cloud
State between stable and unstable
Characteristics
Stratus
Low Level
horizontal
stable
no Precip
Characteristics
Cumulonimbus
Unstable
Thunderstorm
Characteristics
Altostratus
horizontal
middle family
stable
no Precep
Characteristics
Nimbostratus
horizontal
stable
Precipitation
High Clouds
Base between 16.000 - 45.000 AGL
Cirrus - CL
Cirrostratus - CS
Cirrocumulus - CC
Characteristics
Cirrostratus
horizontal
Stable
Characteristics
Cirrocumulus
Unstable
vertical
no Precep
Cloud Indications for Flight
CU, CB: Avoid
ST : Prepare for Alternate Airport
What kind of cloud would you expect at low altitude in unstable environment?
Cumuliform
What kind of cloud would you expect at low altitude in a stable environment?
Stratiform
Dry air consists of?
78% Nitrogen
21% Oxygen
1% Noble Gas
In addition to the gases present in dry air, natural air contains a variable amount of?
water vapor
condensation nuclei
All fronts are….
… Low pressure
During stagefield training and frontal passage, what would you expect to happen to wind direction and speed?
an approx. 90 degree shift in wind direction and wind speed based upon current pressure gradient force
What happens as warm air is lifted over a cold air mass?
It lifts, cools with altitude, condesnes, creates clouds and makes weather
Cold Fronts
Steepness of slopes
Steeper Fronts cause more severe weather
Cold Fronts
Speed
average 25 - 35 kts
Cold Fronts
Direction
SE
Warm Fronts
Speed
Slower than Cold Fronts
Warm Fronts
Direction
NE
The entire local flying area is covered in ST, NS and AS clouds. What type of front?
Stable warm front
You are approaching the clouds in the following order: CS, AS and NS. What changes in ceiling, visibility and chance of precipitation can your expect?
ceiling and VIS decreases
chance of precipitation
Stationary Fronts
Winds
Parallel to front
180 degree shift
Stationary Fronts
Speed
less than 5 kts
Stationary Front
Direction of Movement
unpreditable
Why is the occluded front considered more complex than the others
It is a combination of both cold and warm front weather
Flight Procedures
Cold Fronts/ Squall Lines
LAND and WAIT for it to pass!
Flight Procedures
Warm/ Stationary Fronts
Prepare for alternate Airport
Flight Procedures
Frontal Wave
Handle each front individually
Flight Procedures
Occluded Fronts
WARNING! Circumnavigate or land.
Fog visibilty
less than 5/8 sm
mist visibilty
equal or greater than 5/8 SM
describe the formation of advection fog
prevailing wind blows moist air over colder ground
What kind of fog would you expect as air is lifted on the the windward side of a mountain
Upslope fog
types of icing
Frost
Rime Ice
Frost
Ice crystals formed by deposition of water vapor contacting a cold surface
Rime Ice
Forms from supercooled water droplets
Clear icing
Forms from LARGE supercooled water droplets
Mixed Ice
Combination of Rime and Clear Ice
Freezing Rain
Freezing rain froms when rain droplets fall thru a frontal inversion int a layer of air which has subzero termperature
Categories of Icing
Trace - no hazard < 1 hr w/o de-icing equip
Light - may cause problem > 1 hr
Moderate - contact is dangerous, de-icing needed
Severe - de-icing equipment fails
Hazards of icing
Loss of autorotative capability
Reduces lift
Increases drag and weight
Reduces the speed at which the rotor will stall
Reduces VIS when ice forms on windshield
Reduces airflow to engines when ice forms on screens
Pitot and/ or static source icing results in instrument error
Where would be a likely frontal location to find freezing rain
Ahead of warm fronts
Does severe icing impact your flight?
Yes
Thunderstorm development factors
Unstable or conditonally unstable air
High moisture content
Lifting action
Thunderstorm Types
Air mass - Surface heating/ Convection
Orograhpic - Terrain effects
Frontal - Caused by fronts
Thunderstorm Stages
Towering Cumulus
Mature Stage
Dissipating Stage
The most important element of weather, usually not found above the troposhere is?
water vapor
Atmospheric circulation occurs in all three-cell pattern because of uneven heating of the Earths surface, the 23.5° tilt of the Earth and?
Coriolis Force
The prevailing wind direction between the 30° and 60° latitudes moves FROM which direction?
West
What is a source of warm, moist air mass?
Gulf of Mexcio
What classification would describe a cold, dry air mass?
cP
List four types of heat transfer
Radiation
Conduction
Advection
Convection
How is heat transferred by radiation?
electromagnetic waves
Standard temperature lapse rate?
2°C
A layer of air with an increase of temperature with altitude
Temperature Inversion
What would prevent noctural temperature inversion?
Overcast Sky, Greenhouse Effect
Cold, dense air lifting warmer, less dense air is what Temperature Inversion?
Frontal
Standard MSL pressure
29.92 Hg or 1013.25 hP
Sky conditions associated with low-pressure areas are normally produced by?
rising and cooling of the air
What is an isobar?
An isobar is a line connecting points of equal pressure corrected to mean sea level, drawn 4 mb apart
Wind moves approx. in which direction along isobars?
parallel
Wind direction for Highs
Clockwise away from the High, ~ parallel to isobars
What causes the shift in wind, flowing across the isobars rather than parallel to the isobars?
Surface friction
Wind from left means?
Flying to a Low
Closer Isobars are causing?
Stronger winds
Vapor to solid?
Solid to Vapor?
Deposition
Sublimation
Large Dewpoint spread?
Low relative humidity
Temperature changes caused by density changes are which process?
Adiabatic process
Two basic cloud types?
Stratiform und Cumuliform
Clouds for noctural cooling process?
Low Stratus and Fog
Nimbostratus
NS
Stratus
ST
Cirrus
Cl
Cumulus
CU
Altostratus
AS
Cirrocumulus
CC
Cirrostratus
CS
Stratocumulus
SC
Cumulunimbus
CB
Altocumulus
AC
CU
Low altitude
unstable
vertical cloud w/o precipitation
CB
Low altitude
unstable
vertical cloud producing rain
possible hail
icing
Lightning
SC
Low altitude
conditionally unstable cloud having both horizontal and vertical movement
NS
Middle altitude
stable
horizontal cloud producing rain
ST
Low altitude
stable
horizontal w/o rain
Primary reason for frontal weather
the lifting of warm air by colder air
The frontal inversion of any front always slopes over the _____ air and the precipitation is associated with it normally occurs in the ____ air
cold, cold
Types of air masses in the USA for fronts
Polar and Tropical
All fronts have temperature inversions?
True
Four discontinuities of Fronts
Temperature change
Dew Point change
Pressure change
Wind shift
Define a cold front
Leading edge of a cold air mass
Speed and Slope of a cold front
25 - 35 kts
1:80
Cloud type and width of a cold front
Cumuliform and narrow
Cold fronts move to the?
SE
Wind behind and in front of a Cold Front
NW
SW
Sever line of thunderstorms, with destructive wind, possible hail and CB clouds are called ___?
Squall lines
Procedure in the vicinity of a cold front
Land and wait
Define Warm Front
The trailing edge of a retreating mass of cold air; with warm air moving in behind the frontal symbol
Slope of a Warm Front
1:200
Warm fronts move to?
NE
Wind behind and in front of Warm front?
SW
SE
Weather for Warm fronts
large area of ST, NS, AS w/ rain and fog
Location of warm front weather
80 miles behind the front w/ possible breakes
Conditions for embedded thunderstorms in CB
Warm air lifted by warm front is unstable
Flight planning in vicinity of warm fronts
Alternate airport and fuel for it
Weather for Stationary Front
Same as Warm Front but less intense
Wind direction for Stationary Front
parallel to Stationary front line
Stationary Front Speed
0 - 5 kts
Stationary Fronts can become
Frontal waves
Frontal waves may become
Occluded fronts
Cold front catches up with warm front becomes?
Occluded front
Why has an occluded Front the most severe Weather?
Warm and Cold Front weather occurs at the same time and location
Procedure for Occluded Fronts?
Fly around or land
Four conditions for (Radiation) Fog
Small Temperature/ Dew Point spread
Abundant condensation nuclei
Light sfc wind
Cool land sfc w/ warm air above
Dissipation factors of fog
Heating
Strong wind
Greenhouse effect/ OVC
Formation of radiation fog
At night, terrestrial radiation cools the sfc. The sfc cools the lower layers of air to the dew point.
Formation and location of precipitation fog
Precipitation-induced fog is created as rain falls through a frontal inversion and saturates the cooler air below.
Found ahead of a warm front or behind of a cold front
2400L, SKC, wind @ 4kts, 2°C Temp/DewPoint spread makes?
What happens when faster winds occur?
Fog
SKC
Guld Coast, cold ground, warm & moist air inbound (~5kts)
Advection Fog for a large area
Moist air is mechanically lifted
Upslope Fog
OVC over late evening Fog
Slows down dissipation of Fog
Milky, granular shaped icing?
Rime
Clear Ice droplet size?
Large
Ice intensity that forces an immidiate diversion from altitude?
Severe
Location for Freezing rain
Warm front
Weather to expect close to a High
Sinking air
SKC
weak pressure gradient force
Wind directions
High
Low
Clockwise away
Counter-clockwise towards
TS Conditions
Unstable air
Low Temp/DewPoint spread
lifting action
A severe line of TS that form ahead of a fast moving cold front
Squall lines
Summertime TS forming every day afternoon
Air Mass TS
Mechanical lifted TS on Mountains
Orographic TS
Three stages of a TS
Cumulus
Mature
Dissipating
Most turbulent stage of TS
Mature
Indication for start of Mature Phase of TS
Rain and downdrafts
Flight Procedure for TS induced by thermal activity?
Circumnavigate or land
The OWS Turbulence Chart is dran for what CAT?
CAT 2
If a/c is rated CAT 3… Turbulences stronger or weaker than depicted?
weaker
Microburst in rain
Wet microburst
Microburst with virga
Dry
Dry microburst conditions
CU
Afternoon (hottest part of day)
Hottest time of the year
Ceilings in JET
See METAR
High moisture means
less density
