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01-C: Weather Information

Knowledge

K1: Sources of weather data (e.g., National Weather Service, Flight Service) for flight planning purposes

K2: Acceptable weather products and resources required for preflight planning, current and forecast weather for departure, en route, and arrival phases of flight such as

K2a: Airport Observations (METAR and SPECI) and Pilot Observations (PIREPs)

  • METAR

    • indicate surface-level conditions (as opposed to in-flight conditions such as AIRMET/SIGMET/convective SIGMET)
    • sequential following a prescribed format
    • preceeded by Letter K
    • can be update under certain conditions with a SPECI METAR
    • elements
      • contains
        • winds (AGL, to enable easy minimums decisions)
        • visbibility
        • precipitation
        • cloud coverage
        • temperature
        • altimeter setting
    • Weather conditions:
      • BR: Brume (mist, vis >= 5/8 SM)
      • FG: Fog (vis < 5/8 SM)
      • FU: Fumee (smoke)
      • GR: Grele (hail)
      • TSRA: Thunderstorm and Rain
      • RA: Rain
      • SHRA: Showers of rain
      • SHGR: Showers of hail
      • FZRA: Freezing rain
      • FZFG: Freezing fog
    • Quantifiers:
      • +: heavy
      • -: light
    • Remarks:
      • RAB35: rain began at 1835Z

  • PIREPs:

    • codified in https://www.faa.gov/air_traffic/publications/ATpubs/FSS/fss0902.html
    • PIREP: RFD UUA /OV RFD090005/TM 1818/FL015/TP B767/RM +/- 15 KTS ON FINAL
      • UUA or UA (Upper Air)
        • UA: Routine
        • UUA: Urgent
      • /OV: Over - 5 Nautical Miles east of RFD
      • /TM: Time Zulu
      • /FL: Altitude 1500 MSL; UNKN: Unknown; DURC: During Climb; DURD: During Descend
      • /TP: Type (e.g., B767: Boeing 767; BE90: Beechcraft King Air 90)
      • /RM: Remarks
    • PIREP FWN UA /OV SAX030020/TM 0320/FL300/TP E75S/TB CONS LGT OCNL MOD CHOP
      • FWN
        • Sussex Aiport
      • UA:
        • Routine PIREP
      • OV SAX030020
        • 030 (20 Nautical Miles northeast Of VOR SAX)
      • TM 0320
        • at time 03:20 Zulu
      • FL300
        • at Flight Level 3000
      • TP E75S
        • in Type Embraer 175
      • TB CONS LGT OCNL MOD CHOP
        • Turbulence
        • Continuous light, occasionally moderate chop
    • Other codes:
      • /SK: sky condition, ABV: Above; BLO: Below; CLG: Ceiling [in MSL; as opposed to METARs which use AGL to simplify reporting by pilots using their altimeter]
      • /WX: Weather
      • /TA: Air temperature
      • /WV: Wind vector (direction and speed)
      • /TB: Turbulence
      • /IC: Icing; LGT: Light; MOD: Moderate; SEV: Severe

  • SPECI: Special Reports

    • produced between hourly METARs in case of drastic weather changes (Aviation Weather Handbook, Chapter 24 lists the conditions for a SPECI, e.g., a windshift)

  • Categorical Outlooks:

    • LIFR: Ceiling less than 500 feet and/or visibility less than 1 mile
    • IFR: Ceiling 500 to less than 1000 feet and or visibility 1 to less than 3 miles
    • MVFR: Ceiling 1000 to 3000 feet and/or visibility 3 to 5 miles inclusive
    • VFR: Ceiling greater than 3000 feet and visibility greater than 5 miles, or sky clear

  • Further Acronyms: CIG: Ceiling

K2b: Surface Analysis Chart, Ceiling and Visbility Chart (CVA)

  • GFA: "Prog Chart", i.e., Surface Analysis Chart and Surface Prog Chart

    • shows weather of frontal analysis and precipitation
      • current: Surface Analysis Chart
      • forecast: Surface Prognostic Chart
        • Short-Range Surface Chart
    • including
      • precipitation areas
      • high pressure systems (blue)
      • low pressure systems (red)
      • cold fronts (blue with triangles)
      • warm fronts (red with round pips)

  • GFA: "Signficant Weather Chart", i.e. Low-Level Significant Weather Chart (SigWX chart)

    • features
      • icing (blue)
      • turbulence (orange / red)
      • jet stream
      • cumulusnimbus
    • best used to avoid signficant turbulence and freezing
    • symbolism
      • single hat symbol
        • indicates moderate turblence
        • the number and slash (e.g., 180/) indicates the top of the turbulence, not the base

  • GFA: "Observations", i.e., Weather Depiction Chart

    • showing the METARs per station

K2c: Terminal Aerodrome Forecasts (TAF)

  • applicablity
    • specific to an airport and its 5 SM radius
  • elements
    • contains
      • winds (AGL, to enable easy minimums decisions)
      • visbibility
      • obstructions to vision
      • cloud coverage
    • does not contain
      • temperature
      • cloud tops
    • only reported cloud type
      • cumulonimbus

K2d: Graphical Forecasts for Aviation (GFA)

  • radar weather reports
    • indicate a precipitation's
      • location
      • type
      • intensity
      • cell movement
    • do not indicate
      • trend
  • wind flag shows WINDS FROM
    • long lines are +10 kts
    • half lines are +5 kts
    • triangles are +50 kts
    • red lines are gust factors

K2e: Wind and Temperature Aloft Forecast (FB/FD)

  • units: True & Knots
  • encoding: e.g., 2332+02, means winds from 230 True at 32 knots, temperature +2 degrees Celcius
  • 9900 is read as LIGHT AND VARIABLE with winds less than 5kts
  • usage
    • most favorable altitudes regarding winds
    • areas of possible icing: +2 °C to -20 °C
    • temperature inversions
    • turbulence

K2f: Convective Outlook Chart (AC)

  • Implictations
    • Expect:
      • Windshear turbulence to be expected (dangerous)
      • precipitation static / St. Elmo's fire (not dangerous)
    • Don't necessarily expect
      • steady rain

K2g: Inflight Aviation Weather Advisories including Airmen's Meterological Information (AIRMET), Significant Meterological Information, and Convective SIGMETs

  • three types of Inflight Aviation Weather Advisories:
    • AIRMETs
    • SIGMETs
    • Convective SIGMETs
  • AIRMET
    • issued every 6 hours
    • types
      • AIRMET Sierra: ([S]hitty weather / [S]tatute Miles of Visibility Low) IFR/Mountain Obstruction
      • AIRMET Tango: [T]urbuluence/Wind
      • AIRMET Zulu: Free[Z]ing/Icing
  • SIGMETS in the ConUS
    • issued as needed
    • are issued for
      • non-convective weather (i.e., not associated with thunderstorms) that is hazardous to all aircraft
      • triggers:
        • severe version of the respective AIRMETs
          • severe icing not associated with thunderstorms
          • severe or extreme turbulence or clear air turbulence not assocaited with thunderstorms
        • non-standard events:
          • widespread duststorms or sandstorms lowering surface visibility to below 3 miles
          • volcanic ash
      • relevant to all aircraft
      • sole source of forecasts for icing conditions

  • Convective SIGMETs in the ConUS(AIM 7-1-6-e-1)

    • issued hourly at H+55
    • issued for
      • severe thunderstorms (strong winds, large hail, tornardoes), i.e., thunderstorms producing
        • heavy precipitation (affecting > 40% of an area at least 3000 square miles) or
        • 50 kts of winds
        • hail 3/4 inch or greater
      • embedded thunderstorms (thunderstorms obscured by massive cloud layers)
      • line of thunderstorms
      • NOT
        • moderate thundestorms (which are still dangerous)

  • FAA Inflgiht Advisory

    • Center Weather Advisory (CWA)
      • not a forecast, but an active hazardous condition

K3: Meterology applicable to the departure, en route, alternate, and destination under visual flight rules (VFR) in Visual Metereological Conditions (VMC) including expected climate and hazardous conditions such as

  • Every physical process of weather is related to heat exchange.
  • The variations of solar radiations on th Earth's surface create changes in weather.
  • During the summer, the sun is higher in the sky than in winter.

K3a: Atmospheric composition and stability

  • atmosphere

    • composition

      • troposphere (tropos: mixing/changing -> weather layer)
      • tropopause
        • weather cap line
        • at around 10km (polar) to 17km (equatorial) MSL
      • stratosphere (stratos -> spread out layer)
        • temperature rather stable
        • temperature inversion twoward the top increasing to 0 °C again due to UV absoroption
      • stratopause:
        • line of 0 degrees of temperature
        • approx at 50km MSL
      • mesosphere (3rd = middle out of five layers)
      • Karman line: airglow
        • line of airglow
        • aurora line
        • line between airspace and outer space
      • thermosphere: 100 - 500 km
        • International Space Station (440km)
      • exosphere
        • 500 km to 10000km

    • ISA standard atmospheric model

      • standard temperature: 15 °C = 59 °F
      • standard pressure: 29.92 inHg = 1013.2075 mbar aka hPa
      • pressure altitude
        • indicated altitude + (29.92 − altimeter Setting) x 1000
        • assumption: lapse rate of 1 inHg per 1000 feet
      • density altitude
        • ISA Temp: 15 − ((pressure altitude / 1000) x 2)
        • density altitude: pressure altitude + 120 x (Outside Air Temp − ISA Temp)
        • assumption: lapse rate of 2 degrees Celcius per 1000 feet

K3b: Wind (e.g., windshear, mountain wave, factors affecting wind, etc.)

  • Katabatic ("downslope") winds are cool, dense air currents that rush downslope due to gravity, often starting from high, cold plateaus or glaciers
    • Examples:
      • Chinook winds are warm, dry, gusty winds that descend the eastern slopes of the Rocky Mountains
      • Mistral (Wind from Central France down to the Mediterranean)

  • Dust Devils (Kleintrombe)

    • requires immediate go-around
    • be preapared to take evasive action

  • orographic lifting:

    • arm air being lifted aloft across a mountain
    • results in adiabatic cooling

  • Windshear

    • definition: a change in wind speed or direction
    • can occur at all altitudes, in all directions
    • Non-convective LLWS: low-level windshear
      • defnitory elements: windshear
        • within 2,000 feet of the surface
        • at least 10kts
      • can be expected in areas of
        • low-level temperature inversion,
        • frontal zones, and
        • clear air turbulence
        • strong upper-level winds (greater than 25 kts)
        • in a temperature inversion zone
    • Higher level winshear:
      • often associated with clear air turbulence (CAT)
    • Severe windshear
      • at least 500 FPM or 15 kts
    • information sources
      • direct
        • Convective SIGMETs
        • PIREPs
        • LLWAS (low-level wind shear altert systems, installed at more than 100 airports)
        • TAFs
      • METARs

  • Turbulence

    • can be expected
      • when frontal passages from stratocumulus clouds
      • when stable air crosses a mountain barrier forming
      • mountain waves
      • in lenticular clouds behind the mountain high above the moutain alitude
        • lens or almond shaped
        • winds of 40/50 knots or more
        • standing type of altocumulus cloud
      • below rotor clouds, i.e., inside the rotor circulation, at or below summit altitude
      • in cap clouds obstructing the summit altitude

  • Sea breezes move inland

    • Cool, dense air from the water moves inland to replace warm air that has risen over the land.
      • Land is more responsive to the sun (see knowledge area K3c below)
      • During the day:
        • The land heats up much faster than water.
        • Therefore, the air above the land becomes warmer and less dense quicker than the air over the water.
        • The lower air density causes it to rise upward (convection).
        • This leaves a lower surface pressure behind.
        • The cooler air over the ocean is denser and has higher pressure.
        • Air moves from high pressure to low pressure.
        • At higher altitude, the risen air over alnd circulates to the ocean.
      • During the night:
        • The air over the land becomes colder much quicker than over water.
        • The air over the water still rises, leaving behind lower surface pressure.
        • The high-pressure air over land moves from land to sea.
        • At higher altitude, the risen air over the sea circulates to the land.

  • Surface friction

    • leads to small differences between wind directions at the surface and winds aloft
    • decreases the effect of the Coriolis force at the surface

K3c: Temperature and heat exchange

  • Land is more responsive to the sun than water (thnk: the pot is hot after seconds long before the water is)

    • water has a higher specific heat capacity (energy first breaks dense H2O bonds into less dense H20 before increasing molecular kinetic energy), thus storing much more energy than solid land which starts vibrating immediatley
    • water changes its aggregate phase when energy enters, immediately loosing the energy it received, thus responding slower
    • water is transparent and distributes the energy of a larger volume, thus the top layer of water doesn't take it all

  • Air over land cools down quicker than air over water.

    • Water has a a higher heat capacity than land.

  • physical process:

    • temperature changes occur due to energy changes of the individual particles
      • diabatic energy change: heat transfer into or out of the volume (thermal energy to thermal energy)
      • adiabatic energy change: no heat transfer, but marcoscopic compression or decompression of the volume due to changes in surrounding pressure (thermal energy to potential energy or potential energy to thermal energy)
        • adiabatic cooling: an air parcel rises, decompresses and thus transfers its thermal energy into kinetic energy of the overlying air, thus losing its thermal energy, i.e., losing temperature
        • adiabatic warming: an air parcel sinks, is compressed by higher pressure air at lower altitude, thus the particles bounce against the higher pressure surroundings, speeding them up, and increasing their temperature

  • (low-level) inversion = low-level temperature inversion (think: Los Angeles)

    • definition: temperature rises with increasing altitude rather than decreasing as normal
    • most frequent type:
      • terrestial radiation on a clear, relatively still night
    • properties:
      • are stable and suppress convection
      • trap smoke and pollutants, causing bad visibliity
      • smooth air
      • poor visibility due to fog, haze, low clouds
      • can create windshear across inversion layers
      • is associated with a stable layer of air

  • thermals:

    • heating of the earth's surface
    • warm ground transfers heat to the cooler overlying air
    • the heated air expands rises, forming a thermal

  • Fahrenheit to Celsius

    • 0 °C = 32 °F
    • 16.6 °C = 62 °F
    • 22 °C = 72 °F

K3d: Moisture/precipiation

  • moist air: air that contains water, but in gaseous instead of liquid state

  • condensation: turning water vapor into liquid

  • moisture is added to unsaturated air by

    • evaporation: from liquid to vapor
    • sublimation: from ice to vapor bypassing liquid state

  • at 100% relative humidity, first results in supersaturation and then forces condensation if condensation nuclei are present

  • steady precipitation preceeding a front is indicative of

    • stratiform clouds with little or nor turbulance

  • showery precipitation is indicative of

    • cumuliform clouds

  • The amount of water vapor which air can hold depends on the air temperature.

    • Cold air contains less water vapor than warm air
    • Every 20 °F increase in temperature doubles the amount of moisture the air can hold.

  • dew point

    • temperature to which air must be cooled (at constant pressure and water vapor content) to become saturated; further cooling leads to condensation.
    • temperature below which water will condensate due to reaching maximum saturation.
    • small dew point vs temperature spread causes fog

  • Cloud, fog, or dew form when water vapor condenses.

  • ice pellets ("freezing rain", Graupel/Eisregen)

    • definition: rain drops freezes as they move to the ground
    • implications:
      • temperature inversion where the higher rain layer is warmer and the lower freezing layer is colder

K3e: Weather system formation, including air masses and fronts

  • pressure

    • static pressure aka ambient pressure is always present, whether an aircraft is moving or at rest
    • the effect of a temperature increase at constant pressure altitude is a density altitude incrase
    • altimeter settings
      • are corrected for terrain elevation therefore do not cause variations in altimeter setting
      • vary due to unequeal heating of the earth's surface
    • effects of pressure changes on the altimeter
      • from high to low, watch out below
        • the altimeter will indicate too high (= higher than actual), so we have to look down to the terrain to avoid colliding with it
      • from low to high, look to the sky

  • low-pressure and high-pressure systems (referring to the pressure at the surface level)

    • summary
      • low pressure: inward (low pressure takes in high pressure systems), upward (low pressure rises), and counterclockwise
      • high pressure: outward, downward, clockwise
      • a high-pressure area or ridge is an area of descending air
      • a low-pressure area or trough is an area of rising air
    • explanation
      • https://www.weather.gov/source/zhu/ZHU_Training_Page/winds/pressure_winds/Pressure.htm#FORCES
    • step 1: creation of a low-pressure system at the surface and resulting front physics
      • due to the sun's heating of the earth surface, air rises in some regions
      • the rising air
        • displaces air sideways in that column (divergence aloft), thus reducing pressure at the ground
        • at the surface, the air below is "refilled" (convergence at surface) from its surroundings
      • a low pressure region is created
      • the pressure gradient pulls in surrounding air masses, but these air masses may have different temperatures (air masses from over waters, from desert regions, from mountains, etc.)
        • some of the pulled in air masses are colder than the center of the low-pressure system, creating a cold front
        • some of the pulled in air masses are warmer than the center of the low-pressure system, creating a warm front
      • the moisture in the rising air condensates forming clouds, precipitation, and bad weather
    • step 2: creation of a high-pressure system at the surface
      • as cool air travels sideways, it hits warmer surrounding air
      • its higher density lead the cool air to sink
      • pulling in more air above (convergence aloft)
      • but displacing air at the ground (divergence at the surface)
      • as the cool air sinks, it gets further compressed, heating it up adiabatically (see definition above)
      • this leads to warm weather at the surface
      • and to higher pressure at the surface
      • the increase temperature decreases relative humidity and dissipates cloudiness
    • top-down view
      • step 3: pressure gradient flow
        • air flows from the high-pressure system to bordering low-pressure systems
        • this means - air flows out of the high-pressure system - air flows in to the low-pressure system
        • isobars = line of equal pressure
          • closely placed isobars = steep pressure gradient = stronger winds
          • widely place isobards = shallow pressure gradient = calmer winds
      • step 4: rotation
        • in the northern hemisphere, all air motion vectors are deflected to the right due to the coriois force
        • motion vectors out of high-pressure systems are deflected to the right, leading to clockwise rotations
        • motion vectors into low-pressure systems are deflected to the right, leading to counter-clockwise rotations,
<--- H --->
is converted to
^     
\ -  H - \
        v


 ---> L <--- 
is converted to
            ^ 
- \   L   \ -
    v

  • side-view:

    • step 5:
      • pressure gradient flow from high to low at the surface
      • is equalize by flow from low to high aloft

  • fronts:

    • front definitions:
      • zone between constrasting air masses
      • boundary between air masses
    • stark discontinuity in
      • temperature (thus actual lapse rate is a good indicator of air mass stability)
      • wind direction
    • less stark change in
      • precipitation
      • cloud coverage
      • relative humidity
      • stability of the air mass
    • types of fronts (https://www.wpc.ncep.noaa.gov/html/fntcodes2.shtml, https://www.noaa.gov/jetstream/wxmaps)
      • Cold front:
        • color: blue
        • shape: triangule pips/barbs (think: triangular, sharp mountains -> cold)
        • direction: pips point toward movement
        • effect: slider under and thus massively pushes up warm volumes of air, thus creating massive lifting action, resultng in
          • cumulus and cumulonimbus clouds
          • heavy rain
          • thunderstorms
      • Warm front:
        • color: red
        • shape: round pips/barbs (think: round, rolling hills -> warm)
        • direction: pips point toward movement
      • Stationary front
        • color: blue and red
        • shape: triangular and round
        • direction: stationary
      • Occluded front
        • pink
        • alternating triangles and semicircles
      • Trough
        • elongated area of realtively low atmoshpheric pressure at the surface
        • low pressure at the surface pulls in air that needs to rise
        • rising air can create cloudiness and precipitation
      • Ridge
        • elongated area of realtively high atmoshpheric pressure at the surface
      • Squall line
        • shape: double ellipses separated by a dash
      • Dry line
      • Tropical wave
      • Frontogenesis
        • shape: dashed line with a pip (triangle or semicircle) on EACH segment
      • Frontolysis
        • shape: dashed line with a pip (triangle or semicircle) on EVERY OTHER segment

  • air mass:

    • definition:
      • large bodies of air with uniform temperature and moisture
    • stability
      • definition
        • the airmass' resistance to vertical matopmotion
        • rising and uplifting motion of airmasses
      • determines type and vertical extent of clouds
      • can be best determined by
        • observing the cloud formations and types of precipitation
          • cumulus clouds: instable air, showery rain
          • stratus clouds: stable air, continuous rain
      • increases
        • as dryness increases (think: desert)
        • from cooling from below
      • decreases
        • as moistness increases (think: Florida summer storms)
        • from warming from below (rising of warm air)
    • stable air
      • has no vertical motion and thus allows clouds to settle, but air is smooth
      • restricted visibility
      • stratiform (= stratus type) clouds
      • precipitation if existing would be continuous or steady rather than showery
    • unstable air causes
      • vertical motion, thus creates a bumpy ride, but pushes clouds up
      • rough turbulence
      • cumuluiform clouds
      • good surface visibility
      • showery precipitation
      • unstable, moist air leads to cumuliform clouds and showery precipiation

  • Water radiates heat slower than the land

  • coriolis force

    • core observation:
      • the earth moves east bound (the horn of africa points in the direction of the rotation)
      • difference in surface point speed 0 km/h
        • a human on the earth's surface on the equator has a velocity of 40'000 km / 24 h = 1666 km/h
        • at the northpole, the surface point velocity is 0 km/h
    • northbound motion in the nothern hemisphere:
      • an mass that is created at the equator moves at 1666 km/h, and as it moves northbound it carries that energy while the earth below is moving slower
      • thus it appears as if the mass is deflected east bound (i.e., right as drawn from the perspective of the motion vector)
    • southbound motion in the northern hemisphere (vice versa):
      • a slow mass that starts somewhere and moves southbound will move slower than the earth below it
      • thus appears to be deflected westward (i.e., again right as drawn from perspective of the motion vector)
    • eastbound motion in the northern hemisphere:
      • we see where the above is going: moving masses are deflected right in the nothern hemisphere, but it's let's obvious for eastward and westward motion
      • this is a difficult case that is surprisingly not discussed much (except, see here: https://physics.stackexchange.com/questions/830024/what-is-an-intuitive-explanation-for-the-east-west-component-of-the-coriolis-for)
      • it uses a different reasoning that the northbound and southbound motion, and so I am not sure if the force strength is equal or not
      • suspected reasoning:
        • assume an air mass is created somewhere in the nothern hemisphere and moves eastward moves tagentially along a latitude circle
        • if not for gravity, the air mass would lift off the ground and keep moving along the local tangent plane
        • but gravity pulls it toward the earth center
        • the line that connects
          • the point on the local tagennt plane far off the ground of earth with
          • the earth center lies right of the latitude circle
        • in conclusion, the eath's center of gravity has pulled the mass down from the latitude circle
        • this reasoning is not about preservation of kinetic energy in comparison to underlying earth motion
    • westbound motionin the northern hemisphere:
      • on a line from a point on the local tangent plane ...
      • ... to an point on the local tangent plane westward ...
      • ... projected onto earth's surface in direction of earth's center is right of the latitude circle
      • thus, the mass is again pushed right
    • the inverse is true on the southern hemisphere:
      • i.e., masses are pushed left from the perspective of the motion vector

K3f: Clouds

  • Cloud taxonomy: divided on the first level by their height range
    • High-level (pre-fixed with cirro/cirrus) [above 20'000 ft]
      • Cirrus (Ci) [wisps, also called Mares' tails]
      • Cirrocumulus (Cc) [fluffy]
      • Cirrostratus (Cs) [uniform base]
    • Mid-level (pre-fixed with alto-) [between 6'000 and 20'000 ft]
      • Altocumulus (Ac) [uniform base]
      • Altostratus (As)
    • Low-level [below 6'000]
      • Cumulus (Cu) [fluffy cotton balls, detached from each other; good visibility; bumpy ride]
      • Stratus (St) [grayish with uniform base; think: English weather; bad visibility; smooth ride], layered clouds, stable air mass
      • Stratocumulus / Cumulostratus (Sc) [Cumulus clumped together to a thick layer]
      • Nimbostratus (Ns) [Nimbo = rain-bearing = gray rain cloud]
    • Towering vertically:
      • Cumulonimbus clouds (thunderstorm cloud in anvil shape)
        • formation requires
          • lifting action
          • unstable, moist air
        • not needed
          • excess of condensation nuclei
        • can cause mammatocumulus or mammatus clouds at its base of the anvil cloud
          • bulge hanging out of the cumulonimbus cloud formed by localized downdrafts
          • indicative of a strong thunderstorms, and strong updrafts, downdrafts, and severe turbulence
  • formation
    • Moist, stable air flowing upslope forms stratified/stratiform/stratus type clouds.
  • precipitation
    • significant precipitation requires at least 4'000 ft thickness

  • cloud effects on the flight:

    • Cumulus clouds (think: cumulating/rising air that travels upward and creates bumps):
      • Unstable air with clearer visibilities
      • Bumpy flight with good visilbyt
      • produces showers
      • turbulunces
    • Stratus clouds:
      • stable air with poor visibility
      • produce steady rain
    • Stratocumulus clouds:
      • Bumpy ride

  • problematic cloud flight strategies

    • scud running: ill-fated attempt to maintain visual contact with the terrain in low visibility and ceiling
    • duck-under syndrome: sneak a peek by descending below minimums during an instrument approach

  • Cloud reporting:

    • Okta scale (eights of coverage)
      • 0: Sky clear
      • 1, 2: Few
      • 3, 4: Scattered
      • 5, 6, 7: Broken
      • 8: Overcast
    • ceiling (acronym: CIG)
      • the lowest broken or overcast layer of vertical visibility into an obscuration
      • Broken or Overcast are considered ceilings

  • lowest cloud layer computation

    • known
      • lapse rate: 2 °C / 1000 ft = 3.5 °F / 1000 ft
    • given
      • surface MSL: 1000 ft
      • surface tmp: 70 °F
      • surface dewpoint: 48 °F
    • computed
      • spread: 22 °F
      • 22 °F spread / 3.6 °F lapse rate ~ 6
      • 6 * 1000 = cloud layer at 6000 AGL
      • ~ 7000 MSL
    • other example wants 4.4 °F of lapse rate

K3g: Turbulence

  • types / causes
    • clear air turbulence (cumulus clouds weather)
    • caused by rotary circulation below mountain waves
    • mechanical mixing
    • mountain wave turbulence
      • conditions (AND)
        • winds of 40 kts or greater
        • blowing across a ridge
        • at stable air
      • extension
        • 100 miles downwind of the mountain
  • flight strategy
    • DO
      • maintain level flight attitude to ride the waves
    • DO NOT
      • try to control altitude or airspeed as this increases stress on the aircraft
      • try to maintain angle of attack as it is too difficult (relative airflow changes continously)

K3h: Thunderstorms and microbursts

  • requirements:

    • high humidity
    • lifting force
    • unstable conditions

  • thunderstorms

    • cumulus stage (developing stage)
      • warm, moist air rises paridly creating strong updrafts
      • no precipitation reaches the ground yet
      • growing cloud
    • phase transition
      • non-continuous downdrafts
      • precipiation
    • mature stage (active storm)
      • both updrafts and downdrafts occur together
      • greatest intensity
      • cumulonimbus cloud
      • weather conditions
      • heavy rain
      • lightning
        • always associated with a thunderstorm, produced by a cumulonimbus cloud
      • strong winds / gust fronts
      • hail
        • ice balls formed in thunderstorm clouds
        • phenomenon:
          • updrafts push rain droplets up in higher freezing layers
          • more and more rain drops freeze onto as they move up and down resulting in larger artifacts
      • tornados
      • turbulence
      • icing
    • phase transition:
      • anvil top formation
    • dissipating stage
      • continuous downdrafts
      • rain-cooled air cuts off warm air supply

  • types of thunderstorms

    • most intense
      • squall line thunderstorms:
        • a continuous line of steady-state thunderstorms along a fast-moving cold front
        • a non-frontal narrow band of active thunderstorms
    • less intense
      • a single steady-state thunderstorms
      • warm front thunderstorms

  • can be caused by

    • fast-moving cold fronts
    • humid air at the surface in summer

  • phenomena in the vinicinty of a thunderstorm

    • lightning always results from (thus is associated with) a thunderstorms
    • wind-shear turbulence

  • flight planning

    • thunderstorms ahead
      • divert
      • overfyling impossible due to altitude tops of 60000 feet
      • flying under them is dangerous

K3i: Icing and feezing level information

  • freezing level
    • the lowest altitude over a location at twhich the air temperature reaches 0 °C
  • conditions for structural icing:
    • 1) Visibile moisture and
    • 2) Temperature at or below freezing (0 °C = 32 °F)
  • dangers
    • affects all forces of flight
      • main dangers
        • reducing lift due to alteration of airflow pattern around the wing, prop, and tail (main danger)
        • increases drag due to increse of air-to-skin friction, adding drag (up to 2x the drag)
      • additional dangers:
        • increases weight and changes balance
    • other effects
      • induce misbalance in the prop or the wings
      • blockage of the sensors (pitot tubes)
  • flight implications
    • Faster than normal approach and landing speed
  • types of icing:
    • based on ice type
      • in-flight strucutral icing
        • Clear Ice / rain ice (PIREP code: CLR):
        • Rime Ice (Raueis) (PIREP code: RIME)
        • Mixed Ice (PIREP code: MX)
      • ground icing
        • Frost Ice
    • based on icing location
      • structural icing
        • wings
        • prop
      • induction system icing
        • air intake
        • carburetor
      • instrument icing
        • pitot tubes
  • accumulation rate
    • highest
      • freezing rain (due to large size)
    • less high
      • cumulus clouds with below freezing temperatures
      • freezing driizzle (might cause lighter rime ice)
  • can be obtained
    • current: from PIREPs
    • forecast: from GFA's flight AIRMET and SIGMET
  • AC:

K3j: Fog/mist

  • Fog (FG)
    • surface-level cloud
    • visibility less than 5/8 SM

  • Mist (BR)

    • visibility: between 5/8 SM and 10/8 SM

  • Fog forms when water vapor in the air cools to its dew point, causing it to condense.

  • Types of fog are differentiated based on the reason of cooling.
    • radiation fog:
      • ground cools overnight and cools the air above it to its dew point
      • most likely form of inland fog
      • no body of water needed
      • most conducive setup
        • warm, moist air over low flatland areas on clear, calm nights
      • conditions
        • high humidity (i.e., a small temperature/dewpoint spread)
        • temperature at around 62 °F (16.6... °C)
        • clear skies
        • calm winds / stable atmosphere that do not transport the fog away
        • small temperature / dew point spread
      • special types:
        • valley fog
    • advection fog:
      • warm, moist air moves over a colder surface
      • driven by winds
      • example
        • an air mass moving inland from the coast in winter
    • upslope fog:
      • driven by winds
      • air cools as it rises along terrain.
    • evaporation (steam) fog:
      • cold air moves over warmer water; moisture evaporates into the air and then condenses.
      • flight implications
        • low-level turbulence
        • icing
    • frontal / precipitation / rain-induced fog:
      • warm rain falling through cooler air near the surface.
    • freezing fog
      • droplets of water condensating on contact (at a condensation nucleus) at 15 °F (-10 °)
    • ice fog
      • requires extreme temperatures, usually in arctic regions (-30 °F to -45 °F)
  • winds
    • required for advection fog and upslop fog

K3k: Frost

  • should be removed prior to flight as it disrupts airflow and reduces lift
  • formation of frost:
    • required conditions:
      • the temperature of the collecting surface is at or below the dewpoint of the adjacent air
      • the dew point is below freezing

K3l: Obstructions to visiblity (e.g., smoke, haze, volcanic ash, etc.)

K4: flight deck instrument displays of digital weather and aeronautical information

  • en-route weather information

    • ATIS
    • ATC
    • FIS-B
      • Flight Information Service Broadcast
      • weather from ground station
      • lags approx. 15 minutes
    • FSS on 122.2

  • weather observation stations

    • ASOS station
      • under NWS (National Weather Surface) control
      • provides the information similar to an AWOS3-PT
      • basis for TAFs
    • AWOS stations
      • under FAA control
    • ATIS broadcast
      • D-ATIS = Digital ATIS
      • absence of sky condition and visibility indicates
        • ceiling at least 5000 feet
        • vsibility at least 5 miles
AWOS Levels reports
AWOS-A altimeter setting
AWOS-AV altimeter setting, visiblity
AWOS-1 wind, temperature, dew-point, density altitude
AWOS-2 AWOS-1 plus visiblity
AWOS-3 AWOS-2 plus clouds and ceilings
AWOS-3P AWOS-2 plus precipitation
AWOS-3PT AWOS-3P plus thunderstorms
AWOS-4 AWOS-3 plus precipitation discriminator, type, accumulation, thunderstorms, and runway surfaces sensors

Risk

R1: Making the go/no-go decision and continue/divert decisions, including

R1a: Circumstances that would make diversion prudent

R1b: Personal weather minimums

  • Ceilings: 3500ft (XC)
  • Visibility: 8SM -> 6SM
  • Winds: 8 kts -> 12 kts -> 17 kts max
  • Cross-winds: 5 kts -> 8 kts -> 7 kts max
  • Gusts: 0 -> 5 kts

1c: Hazardous weather conditions, including known or forecast icing or turbulence aloft

R2: Use and limitations of

R2a: Installed onboard weather equipment

R2b: Aviation weather reports and forecasts

R2c: Inflight weather resources

Skills

S1: Use available aviation weather resources to obtain an adequate weather briefing

S2: Analyze the implications of at least three of the conditions listed in K3a through K3l, using actual weather or weather conditions provided by the evaluator

S3: Correlate weather information to make go/no-go decision