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Meteorology > Thunderstorms > Flashcards

Thunderstorms Flashcards

1
Q

What’s the difference between a tornado and a funnel cloud?

A

Tornado reaches the ground. Funnel cloud doesn’t.

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2
Q

Define: St Elmo’s fire.

A

An extreme case of static electricity discharge visible on some parts of the aircraft.

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3
Q

What is the highest altitude a TS may exist at?

A

Generally, CBs can grow up to tropopause, but in cases of severe updraughts, they may penetrate into the tropopause. In tropical regions, cloud tops may exceed 60,000 ft.

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4
Q

What causes downdraughts in a CB?

A

Precipitation: it partly evaporates, cooling the air which sinks.

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5
Q

What may be an indication that a gust front is present?

A

Roll cloud formation.

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6
Q

Where are squall lines most likely to form?

A

In a warm air mass ahead of a cold front. They are most common over large continental areas.

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7
Q

How long can a squall line be?

A

Several hundred kilometres.

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8
Q

When are the air mass thunderstorms most likely to occur?

A

In the early afternoon.

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9
Q

Define: gust front.

A

Descending air from a TS reaching the ground and then spreading out ahead.

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10
Q

Flight below the CB anvil should be avoided. Why?

A

Because hail may fall from the overhang.

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11
Q

Define: frontal thunderstorms.

A

Thunderstorms caused by a cold air mass undercutting a warm air mass.

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12
Q

If TS clouds have to be overflown, what is the minimum recommended vertical separation from the cloud tops?

A

At least 5,000 ft.

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13
Q

Where can the freezing level be found inside a TS cloud?

A

It is assumed to be at the cloud base due to downdraughts. Icing can be expected anywhere in a TS cloud.

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14
Q

What kind of updraught velocities (at maximum) may you experience in a TS?

A

Up to 50 m/s (100 kt).

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15
Q

Define: squall line.

A

A line of thunderstorms.

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16
Q

What kind of wind velocity may be found in a tornado?

A

200 kt can be exceeded.

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17
Q

What is the difference between gusts and windshear?

A

Windshear is of a more sustained nature and therefore more dangerous. Gusts are shorter and may accompany windshear conditions.

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18
Q

How can altimeters be affected when flying in or near a TS?

A

Local pressure variations and gusts can cause inaccuracies of up to 1,000 ft in magnitude.

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19
Q

What conditions increase the chance of hail?

A

High ELR and high air mass moisture content.

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20
Q

Why is it not a good idea to fly in strong turbulence especially at high altitudes?

A

Because the buffet margin is low.

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21
Q

Sometimes, a CB may become mushroom-shaped. Why is that?

A

A CB will look like a mushroom if it reaches the tropopause where the clouds disperse due to inversion of temperature.

22
Q

Define: overshooting top.

A

A bubble shape above the anvil caused by very strong updraughts.

23
Q

What are the main TS hazards?

A

Severe precipitation, severe turbulence/windshear, hail, funnel clouds, and tornadoes.

24
Q

What signifies the transition from cumulus stage to mature stage of a TS?

A

Heavy precipitation.

25
Q

How far can a gust front be found ahead of a TS?

A

Typically, severe turbulence and gusty conditions can be measured in tens of kilometres downwind of a TS core.

26
Q

What kind of updraught velocities (at maximum) may you experience in a cumulus?

A

Up to 30 m/s (60 kt).

27
Q

How long does the mature stage of a TS last?

A

15 to 20 minutes.

28
Q

What signifies the transition from mature stage to dissipating stage of a TS?

A

Cessation of updraughts.

29
Q

What is a potential TS threat related to aircraft radio/magnetic instruments?

A

Buildup of static electricity which causes radio frequency noise and inaccurate radio navigation indications. Magnetic instruments are useless in areas of heavy precipitation and high static electricity.

30
Q

Is climbing to overfly a TS advisable?

A

No. Severe updraughts may be present above active TS clouds.

31
Q

What is the lower limit of temperature where rain droplets may exist?

A

SCWD can be encountered down to -40°C.

32
Q

What kind of precipitation can be detected by a weather radar?

A

Principally, wet precipitation: hail, rain, ice crystals and snow.

33
Q

Why is flying in a TS hazardous?

A

Because of severe precipitation (possibly hail), icing, lightning, poor visibility, and severe turbulence / windshear. Tornadoes and funnel clouds are also a possibility, which may even be concealed.

34
Q

Where in an aircraft is turbulence felt the strongest?

A

In the rear.

35
Q

List the factors affecting the intensity of weather radar returns.

A

» Distance from precipitation

» Gain setting

» Aerial tilt setting

» Attenuation resulting from intervening heavy precipitation

36
Q

What is the temperature range in which lightning strikes are most likely to occur?

A

From -10°C to +10°C (5,000 ft above or below the freezing level).

37
Q

How many stages are in the TS life cycle and what are they?

A

Three:

» Cumulus

» Mature

» Dissipating

38
Q

Define: virga.

A

Precipitation that doesn’t reach the surface.

39
Q

Regarding weather radar returns, when (and by what margin) should echoes be avoided?

A

Below 20,000 ft, the following echoes should be avoided by at least 10 nm:

» Hooks

» Fingers

» Scalloped edges

» Returns of strong intensity

» Returns indicating strong gradients of intensity

» Rapidly changing returns

40
Q

How many requirements are there for a thunderstorm to develop, and what are they?

A

Three:

» Unstable air

» Adequate supply of moisture

» Uplifting action

41
Q

Sometimes, a CB may become anvil-shaped. Why is that?

A

A CB will look like an anvil if it meets high-altitude jetstreams that deform it.

42
Q

How can we know the ELR on a particular day?

A

From meteorological charts.

43
Q

How can airspeed indicators be affected when flying in or near a TS?

A

ASIs may give false indications due to heavy precipitation and gusts. In such cases it is recommended to fly at constant power/thrust (safe penetration speed).

44
Q

Define: self-propagating storms.

A

A TS is self-propagating if it’s able to feed itself. Typically, SP storms are anvil-shaped which allows separate updraught and downdraught streams as well as continuous reabsorption of precipitation.

45
Q

Define: thunderstorm.

A

A CB that produces lightning.

46
Q

Define: air mass thunderstorms.

A

Thunderstorms caused by composition and movement of air mass.

47
Q

Which conditions may stop a TS?

A

» Lack of moist air

» Lack of uplifting action

» More descending than ascending air in the CB

48
Q

How long does the cumulus stage of a TS last?

A

15 to 20 minutes.

49
Q

Regarding weather radar returns, when (and by what margin) should all echoes be avoided?

A

Above 20,000 ft, all echoes should be avoided by at least 20 nm.

50
Q

Define: dust devil.

A

A tornado on a small scale.

Meteorology (14 decks)

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