Lesson 11

Question 1

What are the 3 requirements for thunderstorm formation

Answer 1

All thunderstorms require:
* Unstable air
* Lifting action to get air moving upward
* High moisture content in the air

Question 2

What are the 2 types of thunderstorms:

Answer 2

• Air mass thunderstorms
• Frontal thunderstorms

Question 3

There are ten areas of concern when flying in or near a thunderstorm. Name a few (5)

Answer 3

Turbulence, Hail, Lightning, Icing, Squall lines, Tornadoes, Low ceiling and visibility, Heavy rain showers, Microbursts, Gust fronts

Question 4

How does icing form on an aircraft?

Answer 4

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.

Question 5

What are the 3 stages in the formation of thunderstorms?

Answer 5

Cumulus stage
Mature Stage
Dissipating stage

Question 6

A thunderstorm is a weather phenomenon produced by what cloud?
What accompanies a thunderstorm?

Answer 6

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

Thunderstorms are always accompanied by thunder and lightning and are usually accompanied
by strong gusts of wind and heavy rain.

Severe thunderstorms can be extremely dangerous and may also produce hail and tornadoes.

Question 7

Describe the cumulus stage

Answer 7

Formation of a cumulus cloud that gradually becomes a towering cumulus
Mostly updrafts and no precipitation

Question 8

Describe the mature stage

Answer 8

Onset of precipitation/highest incidence of precips
Lightning, microbursts, gust fronts, hail, and tornadoes can also occur at this stage.
Updrafts 6000 feet per minute (FPM). downdrafts in the 2000 FPM
Violent turbulence is associated with these updrafts and downdrafts and also icing.

Question 9

Describe the dissipating stage

Answer 9

The onset of precipitation during the mature stage causes thunderstorms to dissipate
The top of the cloud spreads out into an anvil form.

Question 10

Describe air mass thunderstorms

Answer 10

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

Air mass thunderstorms usually form as the result of convection, advection, or orographic lift

Question 11

Describe convection thunderstorms

Answer 11

Convection thunderstorms are caused by the uneven heating of the ground.
Afternoon or early evening and dissipate late
in the evening or overnight.
Slouds are scattered over a large area.

Question 12

Describe Advection Thunderstorms

Answer 12

Cold air passing over a warm surface

Over warm land/Afternoon/Scattered/Northerly flow
Over warm water/morning/close together/southerly flow

Question 13

Describe orographic thunderstorms

Answer 13

Lifted up a slope/Dissipate if wind changes direction/Stationary line

Question 14

Describe frontal thunderstorms

Answer 14

Frontal thunderstorms are caused by humid or unstable air being lifted by the frontal surface. Form in a solid line.

Question 15

Describe cold front thunderstorms

Answer 15

Clouds are in a line parallel to the front.
They dissipate with the movement of the front

Question 16

Describe warm front thunderstorms

Answer 16

embedded in stratiform clouds
not as visible as cold front thunderstorms.
they dissipate with the movement of the front.

Question 17

Discuss turbulence and thunderstorms

Answer 17

The strongest turbulence in a cloud occurs during the mature stage generally between 12 000 and 20 000 feet
(zone of updrafts and downdrafts)

• Below the cloud, downdrafts that race towards the ground cause low-level wind shear

Above the cloud, turbulence is also possible and
outward up to 30 km

Severe turbulence is present in all cumulonimbus clouds.

Question 18

Discuss Hail and thunderstorms

Answer 18

Hail occurs in the mature stage of thunderstorm cells that have more intense updrafts.
from the surface up to around 10 000 to 15 000 feet

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

Question 19

What is lightning?

Answer 19

Lightning is the visible electric discharge produced by a thunderstorm. Lightning is always present in, or in the vicinity of, CBs

Question 20

What are the 4 types of lightning

Answer 20

• In-cloud (also called sheet lightning)
• Cloud-to-cloud
• Cloud-to-ground
• Distant

Question 21

Electricity generated by thunderstorms can cause serious problems for aircraft: List them.

Answer 21

• Punctures to the skin of the aircraft
• Damage to communication and navigational equipment
• Temporary blindness of pilots
• Errors in magnetic compasses
• Disruption to low and medium radio frequencies
• Ignition of fuel vapours (rare)

Question 22

What is a squall line

Answer 22

Squall lines are non-frontal, narrow bands of highly active thunderstorms. They generally
develop ahead of a cold front in moist and unstable air

Question 23

What is a gust front

Answer 23

Result of strong downdrafts in the mature stage of a TS reaching the ground and spreading out horizontally

Question 24

Effects of cloud types on flight. CU

Answer 24

Flying near a CU cloud will result in a bumpy flight beneath and in the cloud.

Question 25

Effects of cloud types on flight. TCU

Answer 25

Flying near a TCU cloud will result in turbulence.
Icing is possible in TCU at altitudes above the freezing level

Question 26

Effects of cloud types on flight. CB

Answer 26

Flying near a CB cloud will result in severe turbulence.
There may also be severe icing.

Question 27

Effects of cloud types on flight. ACC

Answer 27

Flying near an ACC cloud will result in turbulence and icing. Precipitation may also be present with ACCs.

Question 28

What are the hazards associated with CBs. Effects of CBs on aircraft.

Answer 28

Hazards associated with CBs include:
* Rapid changes in barometric pressure
* Abrupt changes in wind speed and direction
* Moderate to severe icing
* Hazardous precipitation
* Electrical disturbances
* Turbulence
* Extreme weather