Thunderstorms Flashcards
Conditions required for development of thunderstorms
Cb cloud only
Conditional instability from surface to above freezing level
Sufficient water vapour to form/maintain cloud
Trigger action/lifting force to increase instability
Describe characteristics and development of stationary thunderstorms (4)
Occur early - mid afternoon
Most likely over land in summer or autumn
No windshear a lot so no tilt to the cloud
Up and down draft mix which weaken storm
Describe 3 stages of thunderstorm and how long they last for convectice localised (stationary)
Formative - 15-20 minutes
Mature - 15-20 minutes
Decaying 1-2 hours
Describe characteristics and development of convective travelling thunderstorms (4)
- Wind shear with height causes thunderstorms to move and therefore tilts cloud which separates up/downdrafts
last longer than stationary as sucks up more moisture
- move in direction of 10,000ft (700hPa) wind
Describe orographic thunderstorms characteristics and development
- Air forced up by mountains
- anytime of day but stronger early-mid afternoon
- can last for days with fresh supply of moisture from sea
Describe characteristics of nocturnal tropical thunderstorms and its formation
- Occur 10º latitude either side of equator. Most active towards dawn and stop by mid morning
Cumulus cloud is formed during the day via convection and remains cumulus cos air is stable. At night the ocean stays warm and air cools creating instability, and now theres no incoming solar radiation at night to burn off cloud top by offsetting the loss of terrestrial radiation which therefore steepens lapse rate.
Consequently temperature at top of cumulus cools down steepening pressure lapse rate and instability
Describe characteristics and development of frontal and convergence-type thunderstorms
Frontal - trigger is the lifting of warm, unstable air at the frontal surface. These tend to form in line grouped along the frontal surface, (squall line) in which they move with the front. They’re embedded in multi layered Ac, As, and Sc cloud.
Convergence - tend form in clusters. If formed on a trough they’re likely to be travelling and will be experience as an increase in heavy showers with Ts often precede and followed by lesser showers.
Describe characteristics and development of surface trough and upper trough thunderstorms
- occur when cold upper air moves over low level warm air in the mid latitudes, large change in temperatures creates instability which usually develop isolated or cluster of storms
Describe characteristics and development of warm front embedded thunderstorms
- Occur infrequently due to stability of warm fronts
- requires large amounts of latent heat released
- caused by cloud formation creating conditional instability
Describe turbulence in thunderstorms
- Superimposed gusts in-between updrafts/down with worst between 12-20,000ft.
updrafts in growing stage, up/downdrafts in mature stage and downdrafts in decaying stage
gust fronts in advance of storm in mature stage
Describe icing in thunderstorms (3)
- severe icing from freezing level up to 10,000ft
- occur between 0-40ºC
- 0 to -12ºC worst icing
What are microbursts in reference to thunderstorms
- Usually last 5 minutes and are 1-4km across
- Air descends at high speed and is colder than surrounding air
- occur during mature stage/onset of downdrafts
- can be dry or wet microbursts
What are gustfronts/first gust
Strong downdraught containing cold dense air spread out horizontally at the base of the storm. Sudden wing change, and lowered temp have characteristics of cold front.
Occurs in mature stage on leading edge of storm and is felt 24-32km ahead and up to 6000ft in depth. warm air above travels into storm creating shear zone
Describe electrical phenomena (5
- Occurs +/- 5000ft and +/- 10ºC of freezing level
- starts at onset of precipitation/mature
- hail stones gain negative charge when colliding with lighter precipitation
- lighter precipitation rises and hail sinks to bottom of cloud
- 20% strikes earth, 80% stays in cloud
Describe tornadoes in thunderstorms
- Frequently in severe thunderstorm weather where they occur a lot in summer months usually in afternoon. starts horizontal by windshear causing rotation and then is lifted by updrafts rotating it to the vertical
- Maximum diameter of 100-150m
Describe hail in thunderstorms
- Develops due to strong updrafts, SCWD freeze and grow on small hail or snow with large hail stones being encountered just above freezing level and when they get to big for updrafts they fall.
- occurs from surface to 45,000ft
- severe hail between 8 - 25,000ft
Describe visibility in thunderstorms
- Below Cb in downdrafts with heavy showers
- in front of Cb with gust front
- visibility to 1000m or less, in tropics between 100-300m
Describe characteristics of multi-cell thunderstorms
- Caused by gust front
- Creates multiple Cb storms overlapping each other
- Each one will be at a different stage in development
- lasts longer than normal thunderstorm as it regenerates
Describe use of radar to identify thunderstorms (5)
•Strong updrafts cause turbulence/mixing
•Creates large water droplets or hail
•Shows strong return on radar
•Uses Doppler radar
•Can detect motion and intensity
Precautions to be taken by pilots to avoid or minimise effects of flying in vicinity of thunderstorms (8)
- Switch on all de-icing equipment
•Reduce airspeed to avoid structural damage
•All freight/passengers securely strapped in
•Avoid flying underneath
Disengage autopilot
•Avoid abrupt control inputs
•Turn lights to bright
•Find shortest track through storm
Explain the importance of latent heat in development of thunderstorms (ATPL)
- Gives storm more energy
- vapour condensing releases latent heat, increases instability
Describe the effect of entrainment of drier air aloft on the development of thunderstorms (ATPL)
- High speed dry air is injected into the clouds
•Evaporates water droplets absorbing latent heat
•Makes air more dense and sink
•Increases downdraft speeds
Describe process involved in development of lightning (3, ATPL)
- Rising and falling water droplets/hail produce build-up of static electricity
•Positive at top of cloud, negative at mid-level near freezing level
•Builds up then discharges as lightning and thunder
Describe hazards associated with flight in and around thunderstorms (ATPL 5) turbulence
- 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 hazards associated with flight in and around thunderstorms (ATPL 4) gusts and squalls
- Severe load factors imposed on airframe
- causes large fluctuations in GS and Airspeed
- structural damage due to abrupt changes in altitude
- disorientation
Describe hazards associated with flight in and around thunderstorms (ATPL 5) icing
- 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 hazards associated with hail (ATPL)
- Severe skin damage to airframe if hail is large
- noise of hail stones hitting aircraft can be frightening
- damage to instrument sensors and windscreen
Describe poor visibility (ATPL) thunderstorms
- Beneath Cb reduced to 800-1000m
- Within Cb - down to 10m
- Worst in heavy showers or low level clouds in mountains
- reduces situational awareness
Describe tornadoes hazards (ATPL)
•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
Describes hazards for microbursts
Forces aircraft into the ground. Winds intensify for about 5 minutes and dissipate within about 10-20 minutes.
Horizontal extent of 4km and vertical speeds exceeding 100kts
Describe hazards around gust fronts (ATPL)
Reduced visibility
Large changes in wind direction
Describe following hazards of noise (ATPL)
Distracting to pilots and causes fatigue
Associated with lightning, hail, heavy rain, turbulence
Describe hazards with loss of instruments and impairment of accuracy
- 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 characteristics of super-cell thunderstorms (ATPL)
•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
