Weather

Question 1

Lapse Rate

Answer 1

• the rate at which temperature decreases with altitude
• standard temp lapse rate is 2 degrees C per 1000ft (3.5F)
• dry adiabatic lapse rate is 1.1- 2.8C per 1000ft
• standard pressure lapse rate is 1” per 1000ft

Question 2

High and low pressure systems

Answer 2

Air flows from high pressure (more dense) to low pressure (less dense) which creates wind

Question 3

High pressure systems

Answer 3

• high pressure is more dense so the air moves down, once it hits the ground and has no where to go it spreads outward
• high pressure relative to surrounding air
• air flows clockwise, down and out (screw in wood)
• ridge: elongated area of high pressure
• produces generally favorable weather
• could also produce strong winds because high pressure is trying to equalize with low pressure surrounding it

Question 4

Low pressure systems

Answer 4

• low pressure surrounded on all sides by high pressure
• the low pressure is squeezed by high pressure, the less dense air rises
• airflow counterclockwise, up, and in
• trough: elongated area of low pressure
• associated with bad weather
  1. Col: neutral area between 2 highs and/or 2 lows
  2. Pressure gradient force: air that moves from high pressure to low pressure, perpendicular to the isobars

Question 5

Temperature inversions

Answer 5

• Temperature increase w/altitude- exists in layers
• below is a smooth stable layer of air
• above is unstable
• restricted visibility below inversion
• turbulence above inversion due to unstable air
• 2 types:
  1. Surface based temp inversions
• night: cools ground quickly, cool, clear, calm nights
• morning: heats up air overlying ground first (farm areas)
  2. Frontal temperature inversions
• cool air forced under warm air (definition of cold front)
• warm air spreads over cool air (definition of warm front)

Question 6

Types of clouds: 3 things necessary for formation

Answer 6

1. Condensation nuclei (dust, salt, pollution, particles, etc)
2. Moisture
3. Small temp/dew point spread

Question 7

Low clouds

Answer 7

• Surface to 6500’ AGL
• composed of small super cooled water droplets (water cooled below freezing temps w/o freezing)
• types:
  1. Stratus- grey uniform sheet like cloud with relatively low bases in stable air near surface due to cooling from below
  2. Nimbostratus- grey or dark massive cloud that can be several thousand feet thick and contain large quantities of moisture
  3. Stratocumulus- white puffy clouds that form when stable air is lifted
  4. FOG- base of usually 50ft off the ground
  RIME ICE:
  (-15C to -20C)

Question 8

Middle clouds

Answer 8

• 6500’ to 20000’
• composed of large super cooled water droplets
• Types:
  1. Altostratus: flat dense clouds that cover a wide area, minimal turbulence and can contain moderate icing
  2. Altocumulus: patchy clouds of uniform appearance, light turbulence and icing
  MIXED ICE

Question 9

High clouds

Answer 9

• 20,000 to tropopause (60,000’ AGL)
• composed almost entirely of ice crystals
• Types:
  1. Cirrus: composed of ice crystals that usually form above 30,000ft
  2. Cirrostratus: thousands of feet thick, moisture content is very low and they pose no icing hazard
  3. Cirrocumulus: white patchy clouds, look like cotton, form from shallow convective currents at high altitudes may produce light turbulence
• No icing- the moisture is already frozen

Question 10

Extensive vertical development

Answer 10

• any altitude (sfc to 60,000ft)
• composed of all small and large super cooled water droplets, and ice
• very unstable/turbulent
• Types:
  1. Cumulus: puffy white clouds with flat bottoms and dome shaped tops. Indicate a shallow layer of unstable air. Expect turbulence but little icing and precipitation
  2. Towering cumulus- similar to cumulus except with more vertical development. Contain moderate to heavy turbulence with icing, often develop into thunderstorms
  3. Cumulonimbus: large, vertically developed rain clouds. Containing large amounts of moisture, turbulence, icing, and lightning
• first cloud layer can be calculated by:
  (Temp-dp)x1000= cloud height

Question 11

Fog is formed by

Answer 11

• adding moisture to the air

- reducing temperature to dew point

Question 12

Steam fog

Answer 12

• forms when cold dry air moves over warm water
• the warm water evaporates and rises up (water is added to the overlying cold air and it saturates it)
• Ex. Lakes in the morning

Question 13

Upslope fog

Answer 13

• moist air is lifted by rising terrain
• cools with altitude and condenses
• required a 15kts+ wind
• air is adiabatically to its dew point

Question 14

Radiation fog

Answer 14

• forms on cool, calm, clear humid nights
• as surface is cooled by radiation, the overlying air is also cooled to its dew point
• morning warm up “burns off” the fog

Question 15

Advection fog ( often called coastal fog)

Answer 15

• warm moist air moves over a cooler surface
• sfc cools air to DO and condenses
• most often occurs when wind transports air from warmer water to cooler land
• requires wind to develop (15kts+)

Question 16

Precipitation fog

Answer 16

• warm rain falls into a cool pool of air and it saturates it
• adds moisture to the cooler air

Question 17

5 types of fog

Answer 17

1. Steam fog
2. Upslope fog
3. Radiation fog
4. Advection fog
5. Precipitation fog

Question 18

Temperature/ dew point

Answer 18

• when temp and DP are equal, a parcel of air can no longer hold anymore water and visible moisture occurs
• the temp at which air can no longer hold any more moisture (saturated)
• the DP is where a parcel of air becomes fully saturated
• if the temp=DP, 100% relative humidity resulting in fog, rain, ect…
• relative humidity: amount of moisture in air to what it can hold
• effected by humidity
• hot air can hold more moisture then cold air

Question 19

Stable air

Answer 19

(Cool dry air, ie. Arctic winter)

• poor visibility
• stratus clouds (low level 0 to 6,500)
• little to no turbulence
• rime ice (-15 to -20C)
• steady precipitation
• high pressure

Question 20

Unstable air

Answer 20

(Warm, moist air, ie. Tropical, T-storms)
- good visibility 
- cumulus clouds (exist at any altitude)
- rough turbulence 
- clear ice (0 to -10C)
- showery precipitation 
- low pressure 
Stability: the resistance to upward moving air (vertical air)

Question 21

Thunderstorms 3 conditions necessary for formation

Answer 21

1. High moisture content
2. Lifting action (topographic, frontal, thermals)
3. Unstable air

Question 22

3 stages of the life cycle of a thunderstorm

Answer 22

1. Cumulus stage
   - mostly updrafts
   - building of clouds
   - rising air cools to dew point
   - heat released by condensation of moisture helps sustain upward movement of air
2. Mature stage
   - moisture becomes too large and heavy to be supported by the updrafts and begins to fall
   - consists of updrafts and downdrafts
   - most intense stage
   - anvil top to the clouds
   - downward motion of moisture creates downward movement of air
   - air spreads outward at surface producing temp drop and pressure increase
   - surface winds become strong gusty and turbulent
3. Dissipating stage
   - downdrafts increase to overcome updrafts
   - the storm begins to weaken
   - as the lifting capacity is diminished, so is the strength and existence of the storm
   - it starts to kill itself

Question 23

Standard temp and pressure

Answer 23

Unequal heating of the earths surface causes changes in pressure

• 29.92” Hg (in Mercury) at sea level
• 15 degrees C or 57F
• 1013.9 MB
• 14.7 PSI

Question 24

Types of thunderstorms

Answer 24

1. Single cell
   - single thunderstorm
   - usually lasts an hour
2. Multi cell
   - cluster of thunderstorms
   - different stages of development
3. Super cell
   - extremely large single thunderstorm
   - 2 hour duration
4. Embedded
   - a thunderstorm obscured by a massive cloud layer
5. Squall line
   - line of thunderstorms
   - embedded or hidden in the clouds
   - most dangerous and up to 700 miles wide

Question 25

Thunderstorm hazards

Answer 25

Stay clear of thunderstorms by at least 20 NM because the turbulence and hail can extend out to 20 NM

• hazards of thunderstorms:
  1. Turbulence
  2. Hail
  3. Microbursts
  4. Updrafts/downdrafts
  5. Tornados
  6. Icing
  7. Reduced visibility (clouds, precip, haze)

Question 26

Wind shear

Answer 26

• A sudden drastic change in wind velocity and or direction
• Can occur at any altitude
• Most dangerous at low level (final approach)
  Occurs in:
• frontal zones: opposing wind direction between air masses
• low level temperature inversions: cold still air is covered by fast moving warm air
• clear air turbulence (CAT)
• wake turbulence

Question 27

Microburst

Answer 27

• most dangerous type of wind shear
• can produce vertical and horizontal wind shear
• small scale intense downdraft that spreads out in all directions when reaching the surface
• less then 1 NM wide
• last no longer then 15 minutes
• 6,000ft p/minute downdrafts
• 100kt wind sheer possible (50kts in one direction and 50 in another)

Question 28

To protect against wind shear threats, many airports have LLWAS

Answer 28

• low level wind shear alert system
• provides warning against possible wind shear condition
• takes measurements from multiple locations around airport

Question 29

Turbulence 5 types

Answer 29

Anything from light bumps to extreme jolts

1. Mechanical
2. Frontal
3. Convective
4. Wake turbulence
5. Clear air turbulence

Question 30

Mechanical turbulence

Answer 30

• obstructions or terrain that disrupt airflow

Question 31

Frontal turbulence

Answer 31

• up/down drafts created by frontal impact

Question 32

Convective (thermals) turbulence

Answer 32

• hot pockets of rising air

- ground heats up unevenly, creates thermals

Question 33

Wake turbulence

Answer 33

• created off airfoils
• must be avoided for safe flight
• quartering tail wind keeps vortices over runway longer
• heavy, clean, and slow creates the strongest vortices
• stay 3X the diameter of the rotor away when taxiing

Question 34

Clear air turbulence (CAT)

Answer 34

• typically at higher altitudes (above 15,000’)
• air layers slide over each other
• faster moving top layer creates waves

Question 35

Virga

Answer 35

• precipitation that evaporates before hitting the ground
• creates downdrafts
• cool air sinks faster creating downdrafts
• latent heat of vaporization
• heavy downdrafts up to 6000ft p/min

Question 36

Structural icing

Answer 36

• must have visible moisture
• surface of aircraft must be at or below 0 degrees C
• OAT may be 5 to -20 degrees Celsius
• 5C aircraft (especially rotors) may be colder due to reduced pressure of faster moving air, lowering temperature at point of contact (aerodynamic cooling)
• Venturi effect- velocity of air increases
• Bernoulli principle- as velocity increases, pressure decreases
• boyles gas law- as pressure decreases, temp decreases

Question 37

4 types of structural ice

Answer 37

1. Rime ice
2. Clear ice
3. Mixed ice
4. Frost

Question 38

Rime ice

Answer 38

(-15 to -20 degrees C) temp of AC surface

• small super cooled water droplets that freeze instantaneously upon impact with the surface
• opaque appearance due to air being trapped in the water droplets as they freeze
• brittle
• changes aerodynamics of whatever it forms on (ie airfoils)
• stratus clouds

Question 39

Clear ice

Answer 39

(0 to -10 degrees C)

• large super cooled water droplets freeze slowly
• big rain drops hit surface, blow back as they freeze
• worst heavy, hard to remove, break off in sheets
• rapidly and significantly alters shape of the airfoil
• cumulus clouds or freezing rain

Question 40

Mixed ice

Answer 40

(-10 to -15 degrees C)

• combination of rime and clear ice
• varying size of water droplets that strike and freeze at different rates
• cumulus and or stratus clouds

Question 41

Frost

Answer 41

• forms when water vapor changes directly to ice on sfc that is below freezing (gas–>solid)
• occurs on the ground
• changes aerodynamics: affects ability to produce lift

Question 42

Hazards of structural icing

Answer 42

1. Reduces lift
2. Reduces visibility- forms on windscreen
3. Reduces reception- ice forms on antennas
4. Adds weight/disrupts balance/disrupts airflow
5. Shedding- ice sheds and contacts critical components
6. Instruments- pitot blockage
7. Dynamic rollover- skids freeze to ground