Weather Flashcards
DESCRIBE the characteristics of the troposphere
- adjacent to the earth’s surface.
- It varies in height depending on location and time of year.
- Height Varies from 28,000 to 55,000 ft. Average height over the US is 36,000 feet.
- The temperature normally decreases with increasing altitude.
- Large amounts of moisture is found in the troposphere.
- Winds are generally light near the surface and increase with altitude.
DESCRIBE the characteristics of the tropopause.
- transition zone between the troposphere and starosphere.
- Temperature is constant with altitude.
- The strongest winds (jet stream) is just below the tropopause.
- Contrails form and persist.
- Average height of over the US is 36,000 ft.
- Anvil tops of thunderstorms will spread out at the base of the tropopause.
- A haze layer with a definite top frequently exists at the tropopause.
DESCRIBE the characteristics of the stratosphere.
- Increasing temperature with increasing altitude
- Gas ozone plays major part in heating the air at this altitude
- Excellent Visibility
- Air is thin
- General lack of weather
DESCRIBE the flight conditions associated with the troposphere
- Hazardous weather sometimes exists
- Wind is light near the surface but increases with altitude
- Winds of up to 200 knots may occur near the top of the troposphere
- Nearly all weather occurs here
DESCRIBE the flight conditions associated with the tropopause
- The strongest winds (those of the jet stream) occur just below the tropopause
- Moderate to severe turbulence may be associated with wind shear caused by the jet stream
- Contrails form and persist
- Severe thunderstorms may benetrate the tropopause
DESCRIBE the flight conditions associated with the stratosphere
- Smooth flying with excellent visibility
- The air is thin and offers little resistance to aircraft
- The general lack of weather makes for outstanding flying
DEFINE a lapse rate
The decrease in atmospheric temperature with increasing altitude is called the temperature lapse rate. There is also a pressure lapse rate.
STATE the average lapse rate in degrees Celsius
2ºC per 1000 ft (3.5ºF)
DEFINE atmospheric pressure
Pressure exerted on a surface by the atmosphere due to the weight of the column of air directly above that surface.
STATE the standard units of pressure measurement
Inches of Mercury (in. Hg.) and millibars (mb)
DEFINE the standard atmosphere
A hypothetical vertical distribution of the atmospheric temperature, pressure, and density, which by international agreement is considered to be representative of the atmosphere for pressure-altimeter calibrations and other purposes (29.92 in. Hg. or 1013.2 mb)
DIFFERENTIATE between sea level pressure and station pressure
- Station Pressure is the atmospheric pressure measured directly at an airfield or other weather station
- Sea Level Pressure is the pressure that would be measured from the existing weather if the station were at mean sea level (MSL). This could be measured at sea level or calculated using the standard pressure lapse rate.
DEFINE the types of altitudes
Indicated Altitude is the altitude read directly from the altimeter
Calibrated Altitude is indicated altitude corrected for instrument error.
Mean Sea Level (MSL) or True Altitude is the actual height above mean sea level. It is found by correcting calibrated altitude for temperature deviations from the standard atmosphere.
Above Ground Level (AGL) or Absoulte Altitude is the aircraft’s height above the terrain directly beneath the aircraft and is measured in feet above ground level.
Pressure Altitude is the height above the standard datum plane. The standard datum plane is the actual elevation above or below the earth’s surface at which the barometric pressure is 29.92 in. Hg.
Density Altitude is not a height reference, rather it is an index to aircraft performance. Pressure altitude corrected for nonstandard temperature deviations.
DEFINE indicated altitude
The altitude read directly from the altimeter
DESCRIBE the effects of pressure changes on aircraft altimeters
- If an aircraft flies into an area of lower pressure (without adjusting altimeter setting) its true altitude will be lower than the altimeter indicates.
- altimeter reads high
- High to low, look out below
- If an aircraft flies into an area of higher pressure, its true altitude will be higher than the altimeter indicates.
- altimeter reads low
- Low to high, plenty of sky
DESCRIBE the effects of temperature deviations from the standard lapse rate on aircraft altimeters
- Flying from standard temperature to lower temperature, the aircraft will be lower than its indicated altitude.
- altimeter reads high
- High to low, look out below
- Flying from standard temperature to higher temperature, the aircraft will be higher than its indicated altitude
- altimeter reads low
- Low to high, plenty of sky
EXPLAIN the term pressure gradient
The rate of pressure change over a horizontal distance, as indicated by the spacing of isobars on a surface analysis chart. This isobar spacing represents the size of the pressure gradient force (PGF). Closely spaced isobars indicate a steep (strong) PGF, which is the initiating force for all winds.
EXPLAIN and identify gradient winds and Buys Ballot’s Law with respect to the isobars around pressure systems in the Northern Hemisphere
While the Pressure Gradient Force causes air to flow from high pressure to low pressure, the Coriolis effect (due to the earth’s rotation) acts upon wind to divert the air to the right. Thus, gradient winds:
- Which are found above 2000’ AGL,
- Flow parallel to the isobars,
- Flow clockwise around highs, and
- Flow counter-clockwise around lows.
Buys Ballot’s Law states that if wind is at your back, the area of lower pressure will be to your left.
This pattern of flow exists in the Northern Hemisphere. The opposite is true in the Southern Hemisphere.
EXPLAIN and identify the surface wind direction with respect to the gradient winds in a pressure system in the Northern Hemisphere
For winds below 2000 ft AGL, surface friction plays a role in wind direction, in addtion to the PGF and Coriolis effect. Air flows at angles across the isobars from high pressure to low pressure. Surface winds still move clockwise around highs and counter-clockwise around lows, but since they blow across the isobars at a 45° angle, they also have a component of motion that moves air out of the high pressure and into the low.
DESCRIBE the jet stream
The jet stream is a narrow band of of strong winds of 50 knots or more that meanders vertically and horizontally around the hemisphere in wave-liike patterns.
- Average wind speed: 100-150 knots, but may exceed 250 knots.
- Found in segments:
- 1000 to 3000 miles in length
- 100 to 400 miles in width
- 3000 to 7000 feet in depth.
- Average height 30,000 feet MSL
DESCRIBE sea breezes
The difference in specific heat of land and water causes land surfaces to warm and cool more rapidly than water. Thus land is generally warmer than the ocean during the day. Rising air creates a low pressure over land, while descending air creates a high pressure over the water. The result is wind blowing from the sea, known as a sea breeze, with speeds sometimes reaching 15 to 20 knots.
DESCRIBE land breezes
At night, the circulation near the coast is reversed, so that the air movement is from land to sea, producing an offshore wind called the land breeze. It is typically not as strong as the sea breeze.
DESCRIBE mountain winds
At night, air in contact with the mountain slope is cooled by outgoing terrestrial radiation and becomes denser than the surrounding air. As the denser air flows downhill, from the top of the mountain, it is called the mountain wind.
DESCRIBE valley winds
In the daytime, mountain slopes are heated by the sun, and in turn, they heat the adjacent air. The air near the slope becomes warmer than air farther away at the same altitude, and since warm air is less dense, it begins to rise. It cools as it moves away from the ground and settles back to the valley floor. This downward motion forces the warmer air near the ground up the mountain, and since it is flowing from the valley, it is called a valley wind.
DEFINE saturation
The point where the air contains the maximum amount of water vapor it can hold for that temperature.
DEFINE dew point temperature
(TD) the temperature at which saturation occurs. The dew point is a direct indication of the amount of moisture present in the air.
DEFINE dew point depression
The difference between the air temperature and the dew point temperature (AKA dew point spread).
DEFINE relative humidity
(RH) The percent of saturation of the air. The air can be saturated either by the air cooling to the dew point or by evaporation adding moisture to the atmosphere, increasing the dew point.
DESCRIBE the relationship between air temperature and dew point temperature with respect to saturation
The difference between air temperature and dew point provides an indication of how close the atmosphere is to saturation. The dew point will always be the lower of the two. When the dew point spread reaches about 4°F (90% RH), water vapor will begin to condense into fog or clouds. Any further cooling of the air, or evaporation will produce precipitation.
DESCRIBE the three characteristics of precipitation
- Showers: Sudden beginning and ending, abruptly changing intensity or sky conditions. Usually associated with cumuliform clouds.
- Continuous: Steady. Intensity changes gradually. Associated with stratiform clouds.
- Intermittent: Stops and restarts at least once during the hour. May be showery or steady. May be associated with cumuliform or stratiform clouds.
DESCRIBE the types of precipitation
- Drizzle: very small droplets of water that appear to float in the atmospehere
- Freezing drizzle: drizzle that freezes on impact with objects
- Rain: water droplets that are larger than drizzle and fall to the ground
- Freezing rain: rain that freezes on impact with objects
- Hail or graupel: irregular lumps of ice that develop in severe thunderstorms, consisting of alternate opaque and clear layers of ice. Can cause structural damage to aircraft
- Ice pellets or sleet: small translucent and irregularly shaped particles of ice. Form when rain falls through air with temperatures below freezing.
- Snow: white or translucent ice crystals that connect to one another forming snow flakes. Form at temperatures below freezing.
- Snow grains: very small white, opaque grains of ice. Usually fall in small quantities from stratus-type clouds.
DESCRIBE the four principal cloud groups
- Low clouds: range from just above the surface to 6,500 ft AGL
- Middle Clouds: bases between 6,500 and 20,000 ft AGL
- High Clouds: found above 20,000 ft AGL
- Special Clouds: extensive vertical development
The height of the cloud base, not the top, determines the classification.
Each group is subdivided into cumuliform and stratiform
DESCRIBE the weather conditions associated with low clouds
- Altitude: Just above the surface to 6500’ AGL
- Composition: Water droplets
-
Hazards:
- Proximity of base to surface (most dangerous)
- Collision with terrain dangerous
- Hide thunderstorms
- Icing: accumulates faster in low clouds since they are generally denser than middle or high
- Visibility: Poor
- Precipitation: Light Rain or Drizzle
DESCRIBE the weather conditions associated with middle clouds
Middle Clouds: (ALTO-)
- Altitude: 6500 - 20000 ft AGL (have prefix of Alto)
- Composition: Ice crystals, water droplets, or mixture of two
-
Hazards:
- Dark and turbulent -> formation flying hard
- Icing: Common due to the presence of super-cooled water droplets.
- Visibility: ½ mile to few feet
-
Precipitation:
- Virga: Rain or Snow that evaporates before reaching the ground can be encountered below these clouds
- Rain
- Rain and Snow mixed
- Snow
DESCRIBE the weather conditions associated with high clouds
- cloud bases between 20,000 to 40,000 feet AGL
- prefix “cirro-“ or word cirrus
- Very little effect on flying except for moderate turbulence and limited visibility associated with dense jet stream cirrus.
- Composed mostly of ice crystals
- little or no precipitation
- No icing hazard
- Severe or extreme turbulence found in the anvil cirrus of thunderstorms.
DESCRIBE the weather conditions associated with special clouds
Towering cumulus
- Bases are found at the low to middle cloud heights, but tops extend through the high cloud category
- nearing the thunderstorm stage
- produce heavy rain showers and moderate turbulence in and near the cloud
- Icing is common above the freezing level
Cumulonimbus clouds (CB)
- Thunderstorm clouds
- exceedingly dangerous due to extreme turbulence, hail, icing, and lightning
Nimbostratus
- bases down to 1000 ft AGL
- fog is often present
- Produces continuous rain, snow or ice pellets
- poor visibility and low ceilings, slow in clearing
DESCRIBE the types of atmospheric stability
- Stable: lifted air that is colder than the surrounding air and settles when the lifting action is removed
- Unstable: lifted air that is warmer than the surrounding air and continues to rise after the lifting action is removed
- Neutrally Stable: Lifted air that has the same temperature as the surrounding air and remains at the point where the lifting action was removed.
DESCRIBE the four methods of lifting
- Convergence: convergence of two air masses force the air upward because it has nowhere else to go.
- Frontal: due to the shape of cold fronts, they will lift the air ahead of the cold air mass.
- Orographic: the force of the wind against a mountainside pushes the air upward.
- Thermal: (AKA convective) cool air over a warm surface is heightened by intense solar heating.
DESCRIBE the flight conditions associated with a stable atmosphere
- warm fronts
- warm air mass
- smooth flying
- poor visibility
- rime icing
- steady precipitation
- steady winds
- stratus clouds
- temperature inversions
- low fog
- rising air temperature while climbing
DESCRIBE the flight conditions associated with an unstable atmosphere
- Cold fronts
- Cold airmass
- Turbulence
- Good visibility
- Clear ice
- Showery precipitation
- Gusting winds
- Cumulus clouds
- Thunderstorms
- Towering clouds
- Dust devils
- Rapidly decreasing air temperature while climbing
DEFINE the term air mass
A large body of air that has essentially uniform temperature and moisture conditions in a horizontal plane
- No abrupt temperature or dew point changes within the air mass at a given altitude
- May vary in size from several hundred to several thousand square miles
DEFINE the term front
An area of discontinuity that forms between two contrasting air masses when they are adjacent to eachother
- May be thought of as a boundary between air masses
- May be hundreds of miles long
- Surface front is where the front contacts the ground
DESCRIBE the structure of a front
- Fronts are located in troughs of low pressure.
- Pressure falls, then rises as a front passes.
- Fronts move perpendicular to their depicted line.
- Cold fronts move faster than warm fronts.
- The Greatest contrst between air masses exists at the surface.
- Generally see a 90° wind shift as the front passes.
DESCRIBE the discontinuities used to locate and classify fronts
-
Temperature
- Front is named after temperature change.
- Amount and rate of change partially indicates the front’s intensity
-
Dew Point
- Used to determine air mass boundary
- Larger contrast produces more severe weather
- Cold air masses will generally have a lower dew point than warm air masses
-
Wind
- 90° clockwise rotation after frontal passage
-
Pressure
- Falls ahead and rises after frontal passage
Mnemonic: Terrorists Don’t Want Peace
DESCRIBE the factors that influence frontal weather
- The amount of Moisture available (shown by dew point)
- The Contrast in the amounts of temperature and moisture between the two air masses
- The degree of Stability of the lifted Air
- The Slope of the front
- The Speed of the frontal movement
Mnemonic: Marine Corps Saves Salty Sailors
DESCRIBE the conditions associated with a cold front
- Leading edge of advancing cold air mass
- Sometimes violent and unstable conditions develop
- T-Storms (Cumulonimbus)
- Severe turb
- Stability: Unstable (Cumuliform)
- Move: SE at 20kts (average)
- Wind Shift: SW to NW
- Turbulence: Severe
DESCRIBE the characteristics of a squall line
- Line of severe thunderstorms
- Exact cause is unknown
- Forms 50-300 miles ahead of a cold front
- Sometimes forms without a cold front
- Contains severe hazards to aviation
DESCRIBE the characteristics of a warm front
Warm Front:
- Boundary of advancing warm air mass that overtakes and replaces colder air mass
- Creates broad area of cloudiness by overriding cold air mass
- From the fronts surface position to 500-700 miles in advance of it
- Moves about 15 knots, slower than cold front.
- Gradual frontal slope
-
Stability: Stable (Stratiform cloud is the most easily recognizable)
- Cirrus, cirrostratus, altostratus, nimbostratus, stratus, rain, and fog
- Move: NE
- Wind Shift: SE to SW
- Turbulence: Little to None
-
Ceiling and Vis:
- Moisture ahead of Warm front saturates cold air mass
- 300 - 900 ft ceilings
- Vis: drop to zero with drizzle and fog
- Worst in the winter when ground is cold and air is warm
-
Turb and Thunderstorms:
- IF moist: Unstable altocumulus and cumulonimbus clouds can be embbed (VERY DANGEROUS)
- Only Turb should be from embedded tstorm
-
Precip and Icing:
- Begins in middle cloud deck (6500 - 20,000’ AGL)
- Virga forms here and doesnt reach deck
- Virga often forms when going from cold side towards W front
- Drizzle, freezing drizzle, rain, freezing rain, ice pellets, and snow are all possible in a W front
- Shallow slope + wide thick stratiform create large areas of icing
DESCRIBE the conditions associated with a stationary front
- Alternating cold and warm front symbols
- Weather similar to warm front
- Align in any direction
- 180° wind shift across the frontal boundary
DESCRIBE the conditions associated with occluded fronts
Occluded: Faster moving cold front overtakes a slower moving warm front
-
Types: Cold and Warm
- Which front remains in contact with the ground determines type
- Aligned: NW to SE
- Move: NE at speed of front on the ground (Cold- 20knots, Warm- 15 Knots)
-
Wind Shift: 180*
- SE to NW
- Ahead: Same as those ahead of warm front (SE)
- Behind: Same as those behind cold front (NW)
- SE to NW
- Weather conditions a combo of cold and warm fronts
- From the west: Weather associated with cold front
- From the East: Weather associated with warm front
- Most severe weather: 100NM south to 300NM north of the frontal intersection
DESCRIBE the conditions associated with an inactive front
- Also known as dry fronts
- No clouds or precipitation
- Wind shifts and temperature change still occurs
- Marks area of potentially unfavorable flying conditions
LIST the classifications of turbulence used in Pilot Reports (PIREPs)
- Mechanical
- Thermal
- Wind Shear
- Frontal
LIST the intensities of turbulence used in Pilot Reports (PIREPs)
- Light
- Moderate
- Severe
- Extreme
DEFINE the terms used to report turbulence with respect to time
- Occasional: Less than 1/3 of the time
- Intermittent: 1/3 to 2/3 of the time
- Continuous: More than 2/3 of the time
DESCRIBE how thermal turbulence develops
- Also called convective turbulence
- Result of heating from below
- Solar heating
- Cold air moving over a warm surface
- Strength depends on the type of surface
DESCRIBE how mechanical turbulence develops
- Caused by the passage of wind over obstructions
- buildings
- irregular terrain or mountains
- Strength and Magnitude depend on:
- Wind speed
- Rougness of terrain
- Stability of the air
DESCRIBE the cloud formations associated with mountain wave turbulence
- Rotor Cloud
- Forms downwind from and parallel to the mountain range
- Cylindrical shape
- Downward flow has been known to reach the ground
- Cap Cloud
- Cover the top of the mountain
- Remain stationary
- Lenticular Cloud
- Forms on leeward side of the mountain from standing waves
DESCRIBE techniques for flight in the vicinity of mountain waves
- Avoid the turbulence if possible
- Either fly around or at least 50% higher than the height of the highest mountain range
- Avoid the rotor, lenticular, and cap clouds
- Approach at a 45° angle so that a quick turn around can be made
- Avoid the leeward side of the mountain ranges where strong downdrafts may exist
- Be wary of pressure altimeter readings near mountain peaks
- Could indicate more than 2500 ft higher than true altitude
- Fly recommended airspeed for turbulence in your aircraft
DESCRIBE how frontal lifting creates turbulence
- Turbulence is caused by warm air being lifted by the cold front
- Abrupt wind shift between air masses
- Strong vertical currents when warm air is moist and unstable
- It is most severe in fast moving fronts
- No turbulence in a warm front due to little or no lifting
DESCRIBE how temperature inversions are examples of wind shear turbulence
Although an inversion creates a stable atmosphere, strong winds above the calm air in the inversion can cause a wind shear turbulence at the boundary layer between the inversion and the surrounding atmosphere
DESCRIBE how jet streams are examples of wind shear turbulence
- The jet stream could have winds of over 250 knots.
- This change in wind speed in a short distance can creat a significant amount of wind shear.
- Vertical shear is more significant than horizontal shear
- Exit by turning South or changing altitude
DESCRIBE the recommended procedures for flying through turbulence
- Establish and maintain thrust setting consistent with turbulent air penetration airspeed
- Trim the aircraft for level flight
- Control pitch and bank with reference to the attitude indicator
- Don’t make abrupt control inputs
- Don’t chase the altimeter, allow altitude to vary
DESCRIBE structural icing
- Forms on external surfaces of aircraft
- 4 types of icing:
- Clear
- Rime
- Mixed
- Frost
*
STATE the requirements for the formation of structural icing
- Atmosphere must have supercooled visible liquid water droplets (typically clouds)
- Free air temperature and the aircraft’s surface temperature must be below freezing
STATE the temperature range most conducive to structural icing
between 0°C and -20°C
DESCRIBE icing conditions associated with fronts
- Warm fronts:
- Stratiform clouds
- Rime icing
- low rate of accumulation
- widspread area of icing
- Cold fronts
- cumuliform clouds
- clear icing
- high rate of accumulation
- limited area oficing
- Occluded front
- Mixed stratus and cumulus clouds
- Rime, clear and mixed icing
- Rapid and havy accumulation
- widespread area of icing
IDENTIFY the hazards of aircraft icing
- Alters shape of airfoil, changing the stall AOA (most hazardous aspect of structural icing
- Decreases lift, thrust, and range
- Increases drag, weight, fuel consumption, and stall speed
- faulty pitot-static instrument indications
- Inhibits control surface movements
- Disrupts radio antenna communication
DESCRIBE the types of engine icing
-
Induction Icing (AKA inlet icing)
- May occur with clear skies and above freezing temperatures
- Taxi and departure
- Reduced pressures in intake system lowers temperature, causing condensation and ice formation
- Can happen at +10*C
-
Compressor icing
- Forms on inlet screens and compressor inlet guide vanes
- Noticed by a loss of thrust and rapid rise in exhaust gas temperature (EGT)
Both induction and compressor icing could restrict airflow and cause FOD
DESCRIBE ground icing hazards
- Frost
- Usually found first thing in the morning
- Must remove prior to flight
- Deicing fluid is highly corrosive and should not be sprayed down intakes or other openings
- Taxiing through mud, slush, or water
- Splashed on aircraft surfaces
- Can freeze later at higher altitudes and colder temperatures
- Runway braking conditions
- Ice on the runway would make it hazardous to control the aircraft during braking
IDENTIFY the procedures to minimize or avoid the effects of icing
- Avoid known icing conditions
- Visible moisture
- 0 to -20°C
- Avoid low clouds above mountain ridges
- Climb
- Out of visible moisture
- To colder temperatures, since frozen moisture is not an icing hazard
- To warmer temperatures, if you are below a warm front or a temperature inversion
- Descend
- Out of visible moisture
- Below the freezing level
- If visible moisture or the freezing level is on the surface, descending is not an option
- Don’t fly parallel to a front while in icing conditions
- Avoid high AOA or steep turns
- Expect to use more power on final approach
- Always remove ice from airfoils before attempting to takeoff
LIST the intensities of icing used in Pilot Reports (PIREPs)
- Trace: perceptible, but not hazardous. 1 hour
- Light: May create a problem if flight is prolonged in this environment. Occassional use of deicing/anti-icing equipment may be necessary.
- Moderate: Even short encounters are potentially hazardous. Use of deicing/anti-icing equip. or diversion is necessary.
- Severe: Deicing/antiicing equipment fails to control the hazard. Immediate diversion is necessary.
LIST the types of icing used in Pilot Reports (PIREPs)
- Rime ice - rough, milky opaque ice formed by the instantaneous freezing of small super-cooled water droplets
- Clear ice - glossy, clear or translucent ice formed by the relatively slow freezing of large super-cooled water droplets
- Mixed ice - A combination of rime and clear ice
DEFINE the types of visibility
- Visibility: The ability to see and identify prominent unlighted objects by day and prominent lighted objects at night (expressed in statute miles, hundreds of feet, or meters)
- Flight Visibility: The average forward horizontal distance, measured in statute miles, from the cockpit of an aircraft in flight, at which a pilot can see and identify prominent unlighted objects by day and prominent lighted objects by night
- Prevailing Visibility: The greatest horizontal visibility, measured in statute miles, equalled or exceeded throughout at least half the horizon circle, which need not be continuous. (This visibility is what is referenced in METARs)
- Slant Range Visibility: The distance on final approach when the runway environment is in sight
- Runway Visual Range (RVR): The horizontal distance, expressed in hundreds of feet or meters, a pilot will see by looking down the runway fron the approach end.
DEFINE obscuring phenomena
Any collection of particles (other than precipitation) that reduce horizontal visibility to less than 7 miles. (e.g. fog, haze, smoke, volcanic ash, or blowing spray)
DESCRIBE the sky coverage terms that define a ceiling
A ceiling is the height above ground level (AGL) ascribed to the lowest broken or overcaset layer, or the vertical visibility into an obscuring phenomenon (total obscuration).
- Broken is reported when sky cover is 5/8 to 7/8
- Overcast is reported when sky cover is 8/8
- Vertical visiblity is the distance that can be seen directly upward from the ground into a surface based obscuring phenomenon.
DESCRIBE the parameters that define fog
Fog is a visible aggregate of minute water droplets that is
- based at or within 50 feet of the surface,
- greater that 20 feet in depth, and
- reduces the prevailing visibility to less than 5/8 of a statute mile
STATE the requirements for fog formation
- Condensation Nuclei must be present in the air
- the air must have a high water content (low temp/dew point spread)
- light surface winds must be present (1 to 10 kts)
DESCRIBE the two main types of fog
- Radiation Fog occurs due to nocturnal cooling, usually on clear nights when the earth releases relativley large amounts of radiation into the atmosphere, cooling the surface. Fog or low clouds will develop if the temperature reaches dew point. Winds greater than 10 knots will normally dissipate the fog.
- Advection Fog occurs when warm, moist air moves over a cold surface and the air is cooled to below its dew point. Common in coastal areas. Becomes denser as wind speed increases. Can persist for weeks.
DESCRIBE the aviation hazards of ash clouds
Volcanic Ash has severe effects on aircraft and ability to remain airborne. If the eruption occurs at night, or near your time of flight, presence may be unkown until entering the ash cloud. Radar detection is unlikely. Flight in volcanic ash is indicated by torching from engine tailpipe, St. Elmo’s Fire, bright glow in the engine inlets.
Hazards:
- May cause engine malfunctions including flameout
- Will effect all engines of a multi-engine aircraft
- Pitted windscreen, affecting cockpit visibility
- Sandblasting external surfaces
Make 180° turn to escape
What are the basic requirements for thunderstorm formation?
- Moisture
- Unstable air
- Some type of lifting action
- Building up through the freezing layer
Describe the life cycle of a thunderstorm
- Cumulus: updrafts
- Mature: updrafts, downdrafts and hazards
- Dissipating: downdrafts and hazards
DESCRIBE the hazards associated with thunderstorms
Extreme turbulence
- Can cause changes in altitude
- structural damage
- extra stress on the airframe
- effects depend on severity of turbulence and aircraft speed
- Most sever hazard associated with thunderstorms
Gust Front
- Forms on the surface at the leading edge of an advancing thunderstorm
- Can travel 5-20 miles from the thunderstorm
Roll and Wall Clouds
- occur in severe and fast moving thunderstorms
- Indicate the presence of low level wind shear and extreme turbulence
Lightning and Electrostatic Discharge
- Results from separation of positive and negative charge, from water and ice passing in up and down drafts
- Static charge builds up on aircraft while in the clouds
- Can strike aircraft flying in the clear
- strucutral damage is possible
- catastrphic fuel ignition possible
- pilots can experience flash blindness
- static buildup sometimes realeased through St Elmos fire
Tornadoes
- Violent destructive whirling wind accomplished by a funnel shape cloud
- Tornado - touches the ground
- Funnel cloud - doesn’t reach the surface
- Water Spout - touches water surface
Acronym: HIMELT (Hail, Icing, Microburst, Extreme turbulence, Lightning, Tornadoes)
DESCRIBE the signs and hazards associated with microbursts
Signs
- Virga
- Localized blowing dust
- shaft of rain which diverges closer to the ground
- Severe thunderstorms
- heavy rain
- low or no visibility
- gusty winds
- frequent lightning
- tornado activity
hazards
- 2000-6000 fpm downdrafts
- wind velocities ranging from 20 to 200 kts
- area 1/4 to 2 1/2 miles
- last 5 to 10 minutes
- emenates from any convective
- Strong winds are destructive to ground objects
- Many aircraft mishaps have been attributed to microbursts
EXPLAIN how radar can aid a pilot when flying in the vicinity of thunderstorms
- Ground-based weather radar is the most accurate means of tracking thunderstorms. NEXRAD Doppler radar is capable of detecting microbursts and wind shear.
- A direct relationship exists between the strenth of the radar echoes, the presence of aircraft icing and the intensity of turbulence.
- Echo tops above 35,000 ft often contain extreme turbulence and hail
- Ground-based weather radar is most valuable when there are numerous thunderstorms that are obscured by multiple cloud layers. But, information received before takeoff may be worthless by the time the storms are encountered.
- Airborne weather radar can be used to avoid the worst conditions, but still should not be used to penetrate severe thunderstorms.
- Weather radar information that is not up-to-the-minute should not be relied upon.
DESCRIBE the recommended techniques for avoiding thunderstorm hazards
Options in order of priority (Acronym COUT)
- Circumnavigate
- Fly Over the top of the storm (at least 1000 ft above for every 10 kts of wind)
- Fly Under the storm (At 1/3 distance from ground to cloud base)
- Fly Through the lower 1/3 of the storm
- Avoid thunderstorms if at all possible
- Do not venture within 20 miles of any storm cloud with anvils because of the possibility of hail
- Do not attempt to fly under thunderstorms in mountainous regions
- Avoid flying upnder any thunderstorm if possible
- Do not take off or land if a thunderstorm is approaching
- Do not fly into a cloud mass with embedded thunderstorms without airborne weather radar
Penetration:
- Fly perpendicular to minimize time in storm
- At or below freezing level or above the -20°C level.
- Minimum altitude should be 4000 to 6000 feet AGL above the highest terrain
- Establish recommended turbulent air penetration speed
- expect significant deviations in attitude and altitude
- disengage the autopilot
- avoid abrupt control inputs
- secure all loose objects
- tighten lap belt or should harness
- Turn cockpit lights up (in case of lightning)
- turn on pitot heat
DESCRIBE the use of METARs in flight planning
METARs are used to communicate the latest observed weather to meteorologists and aircrew so they can determine the existing weather at the destination or alternate, and whether a field is IFR or VFR. They can also indicate weather trends as well as a comparison between observed and forecast weather.
INTERPRET weather conditions from a METAR
METAR KNPA 082255Z 27004KT 7/8SM R04/4500FT DZ FG SCT000 BKN011 OVC380 19/18 A2997 RMK VIS1/2V1 CIG009V013 FG SCT000 BKN TOPS 027 SLP149
SPECI KNPA 082317Z 31020G30KT 3/8SM R04/2500FT VCTS SCT000 BKN006 OVC380 17/17 A2993 RMK VIS1/8V1 CIG004V008 FG SCT000 BKN TOPS 350 SLP136
DESCRIBE the use of TAFs in flight planning
The TAF gives the forecast weather for your destination and will aid you in planning the type of flight (IFR/VFR), type of approach you require, determining if an alternate is required, and the selection of the best alternate.
DESCRIBE differences in U.S. civil, military, and international TAFs
U.S. civil stations
- include date and time of transmission prior to forcast period (military does not include this)
- Report visibility in statute miles (military uses meters)
- May include probablity of precipitation occurance
- Generally will not forecast an altimeter setting (military forecasts altimeter setting)
International stations:
- Report altimeter setting in millibars and use Q for indicator (e.g. Q1013) (military uses in-Hg and uses the code QNH, e.g. QNH2998INS)
Military stations:
- When stations amend, correct, or have a routine delayed forecast, a remark will be appended to the last line of the forecast with the appropriate time (e.g. AMD2218)
INTERPRET forecast weather conditions from a TAF
KNSE TAF 260909 28004KT 9000 HZ SCT020 SCT200 QNH2998INS
FM1200 26007KT 9000 HZ SCT025 SCT080 BKN250 QNH2996INS VCSHRA
BECMG 1416 9999 SCT025CB SCT250
BECMG 1718 23015G25KT 530004
TEMPO 1902 8000 TSSHRA SCT010 BKN025CB
FM0200 27010KT 9999 SCT030 BKN080 BKN250 QNH3001INS 20/09Z
DESCRIBE the use of Surface Analysis Charts
The surface analysis chart depicts pressure centers, fronts, and barometric pressure lines. It depicts observed weather (past history).
INTERPRET Surface Analysis Charts
DESCRIBE the use of Low Level Significant Weather Prognostic Charts
Depict predicted positions of fronts and pressure centers as well as forecast weather across the country.
DESCRIBE displayed data METARs
A graphic presentation of METARs where reporting stations are depicted on the chart using station models
DESCRIBE weather data on NEXRAD
Precipitation is displayed in varying colors that represent the energy of radar returns, which relates to the intensity of precipitation.
NEXRAD can also display areas of tornadoes, wind shear, and microbursts
DESCRIBE weather data on satellite imagery
Through satellite imagery, one can determine the type and height of clouds as well as the temperature and thickness of cloud layers.
Two types are infrared (IR), which shows temperature diferences between cloud tops and the ground, and visible imagery, which displays the clouds and the earth reflecting sunlight back to the satellite.
DESCRIBE the use of Winds-Aloft Prognostic Charts
Winds-aloft prognostic charts present observed and average forecast flight level winds aloft
DESCRIBE the use of Winds-Aloft Forecasts
The winds aloft forecast can be used to determine expected winds along the route and altitude of flight.
Winds aloft text presents information listed by reporting station, with columns for different altitudes.
Wind info is given four digits, the first two represent the true wind direction to the nearest ten degrees, and the last two represent speed in knots. This is followed by a temperature in celsius.
- 9900 indicates winds are light and vairiable
- 7409 indicates winds of 240°T at 109 knots (subtract 5 from the first digit and add 100 to wind speed)
- 8299 indicates winds of 320°T at 199 knots or greater
DESCRIBE the use of Severe Weather Watch messages
Aviation Severe Weather Watch Bulletins are issued for funnel clouds or tornadoes, or thunderstorms defined by frequent lightning and one or more of the following: 50 knots of wind or greater, or 3/4 in diameter hail or larger
DESCRIBE the use of In-Flight Weather Advisories
SIGMETs (WS) advise of significant meteorological information other than convective activity that is potentially hazardous to all aircraft.
- Valid for 4 hours
- Any of the following weather phenomenon occur or are forecast over an area of at least 3000 sq miles:
- Severe or extreme non-convective turbulence or CAT not associated with thunderstorms
- Severe icing not associated with thunderstorms
- Widespread dust or sand storms lowering visibility to less than 3 miles
- Volcanic erruption and ash clouds
Convective SIGMETs (WST) are issued only for a thunderstorm and related convective phenomena
Convective SIGMET outlook is valid for up to 4 hours beyond the end of the WST and are issued whenever any of the following are expected to occur for 30 minutes or more:
- Tornadoes,
- a line of thunderstorms (60 miles long, 40% of length)
- embedded thunderstorms,
- thunderstorms greater than or equal VIP 4 with 40% coverage
- hail greater than or equal to 3/4 in diameter or wind gusts to 50 knots or greater
The presence of thunderstorms implies the associated occurance of severe or greater turbulence, severe icing, and low-level wind shear
AIRMETs (WA) advise of significant weather phenomena other than convective activity, but at lower intensities than those that trigger SIGMETs. Intended for all pilots in the enroute phase of flight as well as for preflight planning. Valid for 6 hours.
Three types that are issued when condition affects an area of at least 3000 sq miles:
- AIRMET Sierra: widespread IFR (ceillings less than 1000 ft or visibility less than 3 miles) affecting 50% of area or for extenssive mountain obscuration
- AIRMET Tango: moderate turbulence or sustained surface winds of 30 knots or more
- AIRMET Zulu: moderate icing or freezing level data
STATE the letter identifiers of each of the In-Flight Weather Advisories
WS - Sigmet
WST - Convective Sigmet
WA Sierra - Airmet for IFR
WA Tango - Airmet for turbulence
WA Zulu - Airmet for icing
DESCRIBE the use of Pilot Weather Reports (PIREPs)
PIREPs are a valuable source of information used to supplement ground station weather observations.
Pilots are required to submit a PIREP under the following conditions:
- In flight when requested
- When unusual or unforecast weather conditions are encountered
- When weather conditions on an aIFR approach differ from the latest observation
- When a missed approach is executed due to weather
- When wind shear is encountered on departure or arrival.
DESCRIBE the weather data entered on a DD Form 175-1
DD Form 175-1, Flight Weather Briefing, is prepared and used by the local weather office to brief pilots on weather conditions both locally and along a planned route of flight.
