Thunderstorms Flashcards
Describe the conditions required for the development of thunderstorms.
- Cb cloud only
- AT LEAST must have conditional instability from surface to above freezing level
- Sufficient water vapour to form/maintain cloud
- Trigger action/lifting force to increase instability
Describe the characteristics and development of convective localised (stationary) thunderstorms.
- Occur early to mid afternoon.
- Most likely over land in summer or autumn
- No wind shear aloft so no tilt to the cloud
- Updrafts and downdrafts mix with each other which weakens storm
What is the name and length of each stage of a thunderstorm?
Formative = 15 - 20mins
Mature = 15 -20 mins
Decaying = 1 -2 hours
Describe the characteristics and development of convective traveling thunderstorms.
- Wind shear with height causes thunderstorm to move
- Tilts cloud which separates updraft and downdrafts
- Can last longer than stationary as sucks up more moisture
- Move in direction of 10,000ft (700hPa) wind
Describe the characteristics and development of orographic thunderstorms.
- Moist air forced up by mountains
- Anytime of day but stronger early to mid afternoon
- Can last for days with fresh supply of moisture from sea
Describe the characteristics and development of nocturnal tropical thunderstorms.
- Occur 10 degree latitude either side of equator
- Most active towards dawn and stop by mid morning
- Ocean stays warm at night and air cools creating instability
- No incoming solar radiation at night to burn off cloud top
- Still losing terrestrial radiation which steepens lapse rate
Describe the characteristics and development of frontal and convergence-type thunderstorms.
- Air lifted either by front or by low-level convergence
- Frontal storms form a line across the front (squall line)
- Convergence storms form in clusters
- Strongest when fronts move at rapid rate and frontal air is very cold
Describe the characteristics and development of surface trough and upper trough thunderstorms.
- Occur when cold upper air moves over low level warm air.
- Large change in temperature creates instability
- Isolated or cluster of storms
Describe the characteristics and development of warm front embedded thunderstorms.
- Occur infrequently due to the stability of warm fronts
- Requires large amounts of latent heat released
- Caused by cloud formation - creating conditional instability
With reference to flight in and around thunderstorms, describe the development, severity, and areas where turbulence are likely to be encountered.
- Superimposed gusts in-between updrafts/downdrafts
- Worst between 12,000 and 20,000ft
- Updrafts in growing stage, up/downdrafts in mature stage
- Downdrafts in decaying stage
- Gust fronts in advance of storm in mature stage
With reference to flight in and around thunderstorms, describe the development, severity, and areas where icing is likely to be encountered.
- Severe icing from freezing level up to 10,000ft above FL.
- Can occur between 0 and -40 degrees Celsius
- Carburettor icing between -10 and +25 degrees Celsius
With reference to flight in and around thunderstorms, describe the development, severity, and areas where microbursts are likely to be encountered.
- usually last 5 minutes and are 1 to 4km across
- Air descends at high speed and is colder than surrounding air
- Occur during mature stage/onset of downdrafts
- Can be dry or wet microburst
With reference to flight in and around thunderstorms, describe the development, severity, and areas where gust fronts are likely to be encountered.
- Formed by the cold outflow from beneath a thunderstorm
- Occurs in mature stage on the leading edge of the storm
- Can be felt 24 to 32km ahead and up to 6000ft in depth
- Warm air travels into storm creating shear zone
With reference to flight in and around thunderstorms, describe the development, severity, and areas where electrical phenomena is likely to be encountered.
- Occurs +/- 5000ft and +/- 10 degrees Celsius of freezing level
- Starts at onset of precipitation/mature stage
- Hail stones gain negative charge when colliding with light precipitation
-Light precipitation rises and hail sinks to bottom of cloud - 20% strikes earth, 80% stays in the cloud
With reference to flight in and around thunderstorms, describe the development, severity, and areas where tornadoes (if any) are likely to be encountered.
- Maximum diameter 100 to 150m
- Created by super cell thunderstorms
- Develop in summer months usually in the afternoon
With reference to flight in and around thunderstorms, describe the development, severity, and areas where hail is likely to be encountered.
- Develops due to strong updrafts
- SCWD freeze and grow on small hail or snow
- Occurs from surface to 45,000ft
- Severe between 8,000ft and 25,000ft
- Largest hail stone encountered just above freezing level
With reference to flight in and around thunderstorms, describe the development, severity, and areas where poor visibility is likely to be encountered.
- Below Cb in downdrafts with heavy showers
- In front of Cb with gust front
Describe the characteristics of multi-cell thunderstorms.
- Caused by gust front
- Creates multiple Cb storms overlapped each other
- Each one will be at a different stage in development
- Lasts longer than a normal thunderstorm as regenerates
Describe the use of radar to identify thunderstorms.
- Strong updrafts cause turbulence/mixing
- Creates large water droplets or hail
- Shows strong return on radar
- Uses Doppler radar
- Can detect motion and intensity
Explain the precautions that can be taken by pilots to avoid or minimise the effects of flying in the vicinity of thunderstorms.
- Switch on all de-icing equipment
- Reduce airspeed to avoid structural damage
- All freight/passengers securely strapped in
- Avoid flying underneath
Explain the precautions that can be taken by pilots to avoid or minimise the effects of flying in the vicinity of thunderstorms.
- Disengage autopilot
- Avoid abrupt control inputs
- Turn internal lights to bright due to lightning
- Find shortest track through storm
Explain the importance of latent heat in the development of thunderstorms.
- Gives the storm more energy
- Vapour condensing releases latent heat
- Increases instability
Describe the effect of entrainment of drier air aloft on the development of thunderstorms.
- High speed dry air is injected into the clouds
- Evaporates water droplets absorbing latent heat
- Makes air more dense and sink
- Increases downdrafts speeds
Describe the processes involved in the development of lightning.
- Rising and falling water droplets/hail produce build-up of static electricity
- Positive at top of cloud, negative at mid-level near freezing level
- Build up then discharges as lightning and thunder
Describe the hazards associated with turbulence with flight in and around thunderstorms.
- Below the cloud, dangerous during take-off and landing
- Loose articles being thrown around inside cabin
- Pressure instrument error due to lag
- Severe turbulence can destroy aircraft
- Difficult to maintain altitude
Describe the hazards associated with gusts and squalls with flight in and around thunderstorms.
- Severe load factors imposed on airframe
- Causes large fluctuations in ground speed and airspeed
- Structural damage due to abrupt changes in altitude
- Disorientation
Describe the hazards associated with icing with flight in and around thunderstorms.
- Build up of ice on airframe, engine intakes and pitot/static
- Also on the aerials, control surfaces, propeller blades
- Disfigures aerodynamic shape, increasing drag and weight
- Restricts air intake and pressure instrument failure
- Ice shedding can cause damage
Describe the following hazards associated with lightning with flight in and around thunderstorms.
- Temporary blindness of the pilots
- Minor airframe damage
- Magnetic compass = errors of 10s of degrees
- Disruption to electrical equipment
- St Elmo’s fire
Describe the following hazards associated with hail with flight in and around thunderstorms.
- Severe skin damage to the airframe if hail is large
- Noise of hail stones hitting aircraft can be frightening
- Damage to instrument sensors and windscreen
Describe the hazards associated with poor visibility with flight in and around thunderstorms.
- Worst in heavy showers or low level clouds in mountains
- Reduces situational awareness
Describe the hazards associated with tornadoes with flight in and around thunderstorms.
- Can destroy aircraft with strong winds and low pressures
- Loss of visibility
- Large amounts of noise
- Biggest hazard is at low altitudes near the ground
Describe the hazards associated with microbursts with flight in and around thunderstorms.
- Force aircraft into the ground
Describe the hazards associated with gust fronts with flight in and around thunderstorms.
- Reduced visibility
- Large changes in wind direction
Describe the hazards associated with noise with flight in and around thunderstorms.
- Distracting to pilots and causes fatigue
- Associated with lightning, hail, heavy rain and turbulence
Describe the following hazards associated with loss of instruments and impairment of accuracy with flight in and around thunderstorms.
- Loss of current position
- Can fly into worst part of storm and cause engine flame out
- Loss of altitude
- Pilots become overloaded and disorientated
Describe the characteristics of super-cell thunderstorms.
- Vortex of air also called a mesocyclone
- Only thunderstorm to create tornadoes
- Mature stage may last several hours
- More common over land/continental than ocean/maritime
