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ABC > Course 5 - Section 11 - Thunderstorms > Flashcards

Course 5 - Section 11 - Thunderstorms Flashcards

1
Q

Thunderstorm Size

A

A thunderstorm is a weather phenomenon produced by cumulonimbus cloud (CB)

Individual thunderstorms are generally no more than 10NM in diameter but tend to develop in clusters of two or more

Thunderstorm activity may therefore cover a very large area. CBs associated with thunderstorms may extend vertically as high as 70,000 feet

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2
Q

What is required for thunderstorms to form?

A
  • Unstable Air
  • Lifting Action to get air moving upward
  • High moisture content in the air
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3
Q

What are the three stages of thunderstorm formation?

A
  1. Cumulus stage
  2. Mature stage
  3. Dissipating stage
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4
Q

Thunderstorm formation: Cumulus stage

A

The cumulus stage is characterized by the formation of a cumulus cloud that gradually builds up into a towering cumulus

The cloud mostly has updrafts that support the water droplets within the cloud. No precipitation occurs at the cumulus stage

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5
Q

Thunderstorm formation: Mature stage

A

The mature stage of thunderstorm is characterized by the onset of precipitation and is where the highest incidence of precipitation occurs.

Lighting, microbursts, gust fronts, hail and tornadoes can also occur at this stage

Updrafts within the cloud may attain 6000 feet per minute (FPM). As the water droplets grow, they start falling and dragging air down with them, producing downdrafts in the 2000 FPM range

Violent turbulence is associated with these updrafts and downdrafts

Hail only occurs in the mature stage of a thunderstorm

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6
Q

Thunderstorm formation: Dissipating stage

A

The onset of precipitation during the mature stage causes thunderstorms to dissipate

During the dissipating stage, the precipitation cools down the lower part of the cloud. It also breaks the updrafts that are the main source of its energy

The top of the cloud spreads out into an anvil form

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7
Q

What are the two types of thunderstorms (list)

A

Air mass thunderstorms
Frontal thunderstorms

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8
Q

Air Mass Thunderstorms

A

Air mass thunderstorms form when warm, moist, and unstable conditions exist in the atmosphere

While all type of thunderstorms are severe, air mass thunderstorms are sometimes called “ordinary” or “garden variety” thunderstorms because they USUALLY HAPPEN IN ISOLATION

Air mass thunderstorms usually form as a result of CONVECTION, ADVECTION OR OROGRAPHIC LIFT

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9
Q

List the types of air mass thunderstorms

A

Convection thunderstorms
Advection thunderstorms
Orographic thunderstorms

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10
Q

Convection thunderstorms

A

Convection thunderstorms are caused by the uneven heating of the ground

These types of thunderstorms usually occur in the afternoon or early evening and dissipate late in the evening or overnight

With convenction thunderstorms, clouds are scattered over a large area

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11
Q

Advection thunderstorms

A

Advection thunderstorms are caused by cold air passing over a warm surface. They may occur over land or over water

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12
Q

Orographic thunderstorms

A

Orographic thunderstorms are caused by air being lifted by sloping ground. These storms may occur day or night and they dissipate with a change in wind direction

With orographic thunderstorms, clouds form a stationary line

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13
Q

Air mass thunderstorms: Clusters

A

Air mass thunderstorms can form individually or in clusters

Indvidiaul air mass thunderstorms are call SINGLE-CELL THUNDERSTORMS

Large clusters of air mass thunderstorms are collectively known as SUPERCELLS

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14
Q

Frontal Thunderstorms

A

Frontal thunderstorms are caused by humid or unstable air being lifted by the frontal surface.

Clouds form in a solid line several hundred miles long in various stages of development

Frontal thunderstorms are most often associated with cold fronts, however they can also occur with warm fronts

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15
Q

What are the two types of frontal thunderstorms

A

Cold Frontal Thunderstorms
Warm Frontal Thunderstorms

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16
Q

Cold Front Thunderstorms

A

Cold front thunderstorms occur day or night, and they dissipate with the movement of the front

Clouds are in a line parallel to the front

17
Q

Warm Front thunderstorms

A

Warm front thunderstorms are often embedded in stratiform clouds and are not as visible as cold front thunderstorms

Like cold front thunderstorms, they occur day or night, and they dissipate with the movement of the front

18
Q

List the ten areas of concern when flying near thunderstorms

A

-Turbulence
-Hail
-Lightning
-Icing
-Squall lines
-Tornadoes
-Low ceiling and visibility
-heavy rain showers
-microbursts
-gust fronts

19
Q

Thunderstorms and Turbulence

A

Turbulence is found in many types of weather and may be light, moderate or severe. Turbulence affecting aircraft can range from just a annoying bumps to conditions severe enough to cause structural damage

-The strongest turbulence in a cloud occurs during the mature stage in the transition zone between updrafts and downdrafts generally between 12,000 and 20,000 feet
-below the cloud, downdrafts that race towards the ground cause low level wind shear to be present. Wind shear refers to a change in windspeed, wind direction or both, over a short distance resulting in a tearing or shearing effect
-above the cloud, turbulence is also possible (up to several thousand metres) and outward up to 30 km

Severe turbulence is present in all cumulonimbus clouds. Severe turbulence can affect aircraft by damaging airframes and causing abrupt changes in aircraft speed and altitude

20
Q

Roll Clouds

A

a roll cloud is a low level, horizontal, tube-shaped accessory cloud completely detached from the base of a cumulonimbus cloud. Roll clouds are associated with thunderstorms and turbulence

Often a roll cloud will appear on the leading edge of the storm and will mark the position of the eddies or swirls where the wind changes direction. This is also known as the SHEAR ZONE and is most prevalent with cold fronts and squall lines

The roll cloud is also associated with the downdraft reaching the ground, also known as a gust front, and is often the first drastic change in surface wind conditions ahead of an approaching storm

21
Q

Thunderstorms and Hail

A

Hail occurs in the MATURE STAGE of thunderstorm cells that have more intense updrafts

Hail will occur most from the surface up to around 10,000 to 15,000 feet. Hail could happen as high as 45,000 feet

If the clouds are built diagonally, hail that has been carried in the updraft may be case out into the clear air surrounding the cloud from the sides or from the overhanging anvil cloud

Hail can cause damage to aircraft, windshields, outside instrument sensors and even airframes

22
Q

What are the four types of lightning

A

In cloud (sheet lightning)
Cloud to cloud
cloud to ground
distant

23
Q

Lightning and thunderstorms

A

Lightning is the visible electric discharge produced by a thunderstorm.

Lightning is always present in, or in the vicinity of, CBs

Lightning is most prevalent in CBs in the mature stage between the temperatures of +8 and -8 celcius (at +/-5000 feet from the freezing level)

Electricity generated by thunderstorms can cause serious problem for aircraft:
-punctures to the skin
-damage to communication or navigational equipment
-temporary blindness of pilots
-errors in magnetic compasses
-disruption to low and medium radio frequencies
-ignition of fuel vapours (rare)

Static discharges on wind screens, wing tips and propeller tips can cause static on low frequency bands (also known as precipitation static)

Less frequently, and electrical discharge called st elmos fire can appear as a bushy halo around some edges of aircraft

24
Q

Thunderstorms and Icing

A

*** Clear and mixed icing is possible in all stages of thunderstorm cloud development, but SEVERE CLEAR ICING is most likely to occur in the UPPER HALF of a thunderstorm cloud IN THE MATURE STAGE, especially when temperatures are between 0 and -25 degrees C

When an aircraft flies at or below freezing temperatures and strikes supercooled water droplets, the droplets freeze and adhere to the aircraft, the result is icing.

Icing is a major hazard to aviation and is a fact of life in canadian aviation. Conditions can range from light and readily controlled, to extreme and disasterous in flight

Dangerous icing can occur in thunderstorm clouds

25
Q

Thunderstorms and Squall Lines

A

Squall Lines are narrow bands of highly active thunderstorms. They generally develop ahead of a cold front in moist and unstable air.

Squall lines can form rapidly, reaching maximum intensity during the late afternoon or early evening. They can range from one to several hundred miles in length and may be broken or in a continuous line

A squall line can contain severe thunderstorms with torrential rains, large hail, and tornadoes. It contains all the other hazards generally associated with thunderstorms

26
Q

Thunderstorms and Tornadoes

A

A tornado is a violently rotating column of air that extends from the thunderstorm to the ground

Tornadoes sometimes occur with isolated thunderstorms but occur much more frequently with supercell thunderstorms (those associated with cold fronts and squall lines)

They can occur several km outward from teh main area of lightning and precipitation

Tornadoes generate violent turbulence. An aircraft entering a tornado vortex is certain to suffer structural damage. Since the vortex extends well up into the cloud, a hidden vortex could be encountered

27
Q

Cumulonimbus mammatus clouds

A

Cumulonimbus mammatus, or mamma clouds, are often an indication of tornadoes and violent turbulence

These clouds are round shaped and hang under teh cloud base or anvil

28
Q

Thunderstorms and Low Ceiling and Visibility

A

Visibility is generally near zero within a thunderstorm cloud. The ceiling and visibility can also become greatly reduced in the precipitation between cloud base and the ground

Heavy precipitation can saturate the air, rapidly causing low level clouds called stratus fractus and fog to form. As a result, ceiling and visibility are rapidly reduced turning a visual flight rule approach into an instrument flight rule approach

Aircraft will be restricted by the lower ceiling and visibility, but the situation may become even more severe when other hazards are present, such as turbulence, hail, lighting, and low-level wind shear

29
Q

Thunderstorms and Heavy Rain Showers

A

A thunderstorm contains vast amounts of large liquid water droplets

The heaviest rain showers are associated with the MATURE stage of thunderstorm development with the onset of the first downdrafts

Heavy rain showers associated with thunderstorms can CONTAMINATE THE WING SURFACE which may lead to reduction in lift and possible early stall

Heavy rain can REDUCE VISIBILITY and cause refraction on teh windscreen of the aircraft if encountered during approach and landing. This refraction produced the illusion that the runway threshold is lower that it actually is

Water lying on a runway can cause HYDROPLANING, which destroys breaking action of the aircraft and can lead to loss of control

30
Q

Thunderstorms and MICROBURSTS

A

a Microburst is a sudden and powerful downdraft within a thunderstorm

Microbursts can cause sudden and dangerous low-level wind shear, resulting in hazardous conditions for takeoff and landing

31
Q

Thunderstorms and Gust fronts

A

A gust front is the result of strong downdrafts in the mature stage of a thunderstorm reaching the ground and spreading out horizontally

There is usually significant turbulence associated with gust fronts

Nearly all thunderstorms produce some degree of gust front

32
Q

Cumulus clouds and their affect on flight

A

Flying near a CU cloud will result in a BUMPY FLIGHT beneath and in the cloud. There are updrafts below and in the cloud

A CU can develop into a TCU and then a CB

33
Q

Towering Cumulus clouds and their affect on flight

A

Flying near a TCU cloud will result in TURBULENCE

ICING is possible in TCU at altitudes above freezing level

There are strong updrafts below and in the cloud

A TCU may develop into a CB

34
Q

Cumulonimbus clouds and their affect on flight

A

Flying near a CB Cloud will result in SEVERE TURBULENCE

There also may be SEVERE ICING

CBs are accompanied by dangerous hazards such as
-thunderstorms
-precipitation
-wind
-violent vertical currents
-hail
-lightning

35
Q

Altocumulus Castellanus clouds and their affect on flight

A

Flying near an ACC cloud will result in TURBULENCE AND ICING

precipitation may also be present with ACCs

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