High Altitude Weather Flashcards
What is the life span of a thunderstorm
2 hours
What are the stages of a thunderstorm
Cumulus stage - 5000 to 20000ft
Mature stage - 5000 to 40000ft
Dissipating stage - 5000 to 35000ft
What cloud formation indicates the level of the tropopause?
Anvil.
The tropopause often restricts vertical development of cumulonimbus clouds due to the the temperature inversion which results in a wide spread cloud called Anvil
What is needed for the formation of a thunderstorm to occur?
Source of lift (frontal weather, hot land mass)
Unstable air mass
High moisture content
What are squall lines and how are they depicted on a SIGWX chart?
A sudden, sharp increase in wind speed lasting minutes.
Often associated with frontal air mass and thunderstorms
Can be embedded and closely packed together
Depicted on a chart when thunderstorms are listed as frequent (5/8ths or greater)
Where would you more likely see a thunderstorm exceed the tropopause?
The tropics
Would a thunderstorm caused by a bushfire last shorter or longer than one formed due to a frontal air mass?
Shorter
Thunderstorm up and down drafts can produce rates of climb/descent up to what?
5000ft/minute
both within cell and periphery of the cell (in particular under the anvil)
What cloud formation gives a good indication of which direction the wind is traveling at high altitudes?
Anvil
To avoid the storm ensure to fly upwind rather than down wind.
Where can current information on thunderstorms be found?
Sig Wx Charts
Airmets
Sigmets
Satellite imagery
What are common hazards associated with thunderstorms?
Severe updrafts and downdrafts Line squalls Turbulence Severe icing Heavy rain (tropical storms can hold up to 250mil L of water) Hail Lightning
How do you avoid thunderstorms?
Check all available briefing info during planning
Follow company SOP guidance
Use WX radar and correct operating techniques, do not penetrate any yellow or fly close to sharp colour gradients.
Do not attempt to out-climb a building thunderstorm
Do not attempt to overfly a mature or dissipating storm cell
Avoid active thunderstorms 5nm up to 5000ft or by your altitude divided by 1000 there after
Do not take off or land when a mature or dissipating cell is with 5nm of aerodrome due to microbursts and wind shear
What is Upper Atmospheric Lightening (UAL) and where does it occur?
UAL is lightening arcing between clouds or from the tops of thunderstorms to the bottom of the ionosphere.
Although seldom seen by pilots, it is possible within the tropics, mountainous areas with large orographic uplift or over the ocean where large thunderstorms occur.
What are some types of UAL?
Blue Glimpses Blue Jets Red Sprites Tendrils Halo Elve Giant Jets
Arcing between thunderstorms or out the side of thunderstorms in the arid and sub-tropic regions is not to be considered as UAL.
What are the 2 types of turbulence typically found above FL150?
Clear Air Turbulence or CAT
Mountain Waves
What is CAT and how does it occur?
CAT is sudden and severe turbulence or wind shear occurring in mostly cloudless regions which causes violent buffeting of aircraft.
What cloud formations can be indicators of CAT?
Cirrus or Lenticular clouds
What are the 2 mechanisms that cause CAT?
Mechanical - A disruption to smooth horizontal air flow.
Thermal - Caused by vertical currents of air in an unstable atmosphere
What levels are CAT typically experienced and how are areas of CAT avoided ?
7000ft below the tropopause to 3000ft above the tropopause
Strong vertical and horizontal wind shear associated with CAT tends to be shallow and patchy. A change in 2000ft is usually enough to exit the turbulence.
What are some common causes of CAT?
Jetstreams - significant horizontal wind shear
Terrain - rising ground creates disturbances to air flowing over it
Thunderstorms - CB’s have very strong vertical currents, avoid flying over the top or horizontally by a minimum of 5nm or your Altitude divided by 1000, which ever is greater
Unequal Heating - typically found between the cooler air masses over ocean and the warmer air masses over land.
What does this indicate and what chart would you find it on?
The area inside the line indicates the area that moderate CAT could occur between 8000ft and FL200 on a SIGWX Chart.
A double arrow would indicate sever CAT
How do mountain waves form and where does the turbulence associated with them occur.
Mountain waves are the result of air which is forced to rise up the windward side, then due to atmospheric conditions, sink down the leeward side. This develops into a series of standing waves down stream and may extend 100’s of km over clear areas of land or water and in some cases up through the tropopause.
They need:
windspeed of at least 25kts at/and perpendicular to ridge line.
Windspeed increases with height
A stable layer around the ridge height
How can you visibly identify mountain waves?
Lenticular caps over the ridge line Stacked lenticulars (like venetian blinds) downwind of the ridgeline
What is the name of the turbulent air movement in a mountain wave and how do they occur?
Rotors or eddies can be found embedded in mountain waves.
They normally occur when the windspeed changes due to friction with the ground.
They present as turbulence or wind shear.
Clouds will form on the upwind side of the rotor and dissipate on the down flow side if the air is sufficiently moist
