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FSS1601 AK3 > AV20: Thunderstorms - DC > Flashcards

AV20: Thunderstorms - DC Flashcards

1
Q

What are the four conditions required for the development of a TS?

A

High water vapour content
Strong lifting agent
Condensation nuclei
unstable air to high altitude

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2
Q

Define Cell

A

Part of a thunderstorm complex that is in a particular stage of development

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3
Q

Define Cluster

A

Group of cells that form a thunderstorm complex

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4
Q

What are the 3 stages in the life of a thunderstorm?

A

Cumulus Stage
Mature Stage
Dissipation Stage

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5
Q

What are the characteristics of the cumulus stage of a TS? (4things)

A

mainly ascending currents (updrafts)
No precip
Mainly water droplets
Drop in pressure at the surface

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6
Q

What are the characteristics of the mature stage of a TS? (8 things)

A
  • Both strong updrafts and downdrafts
  • Start of Precip (+SHRA, SHSN, SHPL, SHGR)
  • Very high tops of cloud
  • Severe turbulence (gusts, squalls, wind direction changes)
  • All types of lightning
  • Possible microbursts, or +FC
  • Variations in surface pressure and temperature
  • Composed of RA, SN, GR, and IC
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7
Q

What are the characteristics of the dissipation stage of a TS? (7 things)

A
  • Gradual end to precip
  • Anvil top
  • mainly downdrafts
  • little vertical movement in upper portion
  • increased pressure at surface
  • drop in surface temperature
  • contains water drops, SN and IC.
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8
Q

What are the two categories of thunderstorms?

A

Air Mass TS, and Frontal TS

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9
Q

What are the 3 causes of air mass TS?

A 
Daytime heating (convection), 
Advection heating (cold air over warm surface), 
orographic lift
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10
Q

What are the characteristics of a convection TS?

A

Caused by unequal heating of the ground,
Happen in afternoon or early evening,
Scattered over a large area,
Dissipate in late evening / overnight.

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11
Q

What are the characteristics of advection TS - over land?

A

Caused by advection of cold air over a warm surface,
Generally in a northerly flow,
Maximum activity happens in the afternoon,
Scattered over a large area,
dissipate in late evening / overnight.

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12
Q

What are the characteristics of advection TS - over water?

A

Caused by advection of cold air over a warm surface,
Maximum activity in the morning,
Tend to be close together,
dissipates with southerly flow.

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13
Q

What are the characteristics of orographic TS?

A

Caused by air lifted by sloping ground,
In a stationary line (over the lifting point),
Can happen day and/or night,
Dissipates with change in wind direction.

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14
Q

What are the characteristics of a Warm Front Thunderstorm?

A

Humid Unstable air is lifted by frontal surface,
Embedded in stratiform clouds,
day and night,
dissipates with movement of the front.

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15
Q

What are the characteristics of a Cold Front Thunderstorm?

A

Humid / Unstable air is lifted by the frontal surface,
in a line parallel to the front,
day and night,
dissipates with movement of the front

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16
Q

Define Microburst

A

Intense, small scale downdrafts which spread outwards from the downflow centre when they reach the ground

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17
Q

What 2 forms of precipitation are indicators of a POSSIBLE microburst?

A

Showers & Virga

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18
Q

What are the formation requirements for microbursts?

A

Convective Activity,

Downdrafts - created by cooling of the air by evaporation and/or friction on the air caused by falling precip.

19
Q

What happens when the downdraft of a microburst reaches the ground?

A

spreads out in all directions in the shape of a “vortex ring”.

20
Q

What happens at the edge of a vortex ring?

A

airflow curls upwards on itself, which is associated with dangerous low level wind shear for aircraft

21
Q

What is the typical diameter of a downdraft of a microburst?

A

up to 6000 feet (1.8Km)

22
Q

What is the typical diameter of a vortex ring?

A

up to 5 miles

23
Q

What is the typical velocity of the downdraft of a microburst?

A

Up to 6000 feet per min

24
Q

What is the typical velocity of the gust speeds outwards from the center of a microburst?

A

up to 80 Knots

25
Q

What is the typical lifespan of a microburst?

A

10-20 minutes

26
Q

What are the indication signs of a microburst?

A

Dust ring at the surface (dry microburst),
heavy rain shaft (possibly),
VIRGA (sometimes),
Opposing wind directions over a short distance.

27
Q

What are the 9 hazards associated with thunderstorms (for aviation)

A 
Turbulence,
Hail,
Lightning,
Icing,
Squall lines, 
Low Ceilings and Visibility,
\+SHRA,
\+FC,
Microbursts
28
Q

Where is turbulence most pronounced in a TS?

A

In the mature stage in the mid and high levels. Between opposing air currents, especially in and near zones of precip.
AND
Between the air and ground (Sfc to 1000’)

29
Q

At what altitude does the maximum occurrence of hail happen?

A

10000 to 15000 feet

30
Q

The stronger the vertical currents, the ________ will be the hail.

A

larger

31
Q

Define Lightning

A

Visible electric discharge produced by a thunderstorm, always present in or in the vicinity of CB clouds

32
Q

Between what temperatures is lightning most prevalent in CB cloud?

A

+8 to -8 degrees C (+/- 5000 feet from freezing level) in the mature stage

33
Q

How does the stability of the air affect lightning?

A

The more unstable the air, the more lightning activity

34
Q

For lightning to occur, CB cloud tops must reach a temperature of ___________

A

-20 degrees Celsius

35
Q

What are the 3 types of lightning?

A

In cloud (LTGIC)
Cloud to Cloud (LTGCC)
Cloud to Ground (LTGCG)

36
Q

What effects does icing have on aircraft?

A

modifies aerodynamics,
causes engine to stall by blocking air intake,
causes instrument errors by blocking sensors (pitot tube / static port),
reduces visibility.

37
Q

When is icing most common and most severe in a TS?

A

SEV CLR ICG in the upper half of TS in mature stage, especially when temperatures are between 0 and -25 C, but could be down to -40.

38
Q

What is a squall line?

A

A non-frontal band of highly active thunderstorms that generally form ahead of active cold fronts in moist and unstable air, with the gust front acting as a lifting agent.

39
Q

Heavy precipitation saturating the ground or air could cause __________ forming.

A

Fog or SF

40
Q

+SHRA are associated with which stage of the TS?

A

Mature

41
Q

What are some effects +SHRA can have on aviation? (4 things)

A
  • Contaminate wing (causing early stall)
  • Reduced visibility on approach
  • refraction on windshield (also limiting visibility)
  • Hydroplaning on runway (destroyed braking action and possible loss of control)
42
Q

Tornadoes are generally associated with _______________ and ________________

A

Cold Fronts and Squall Lines

43
Q

What type of cloud is a good indicator of possible tornadoes?

A

Mammatus

FSS1601 AK3 (16 decks)

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